Toward a Systematic Understanding of “Heaviness” in Metal Music Production

ABSTRACT “Heaviness” has been one of metal music’s defining features in three decades of metal scholarship. Research acknowledged its essential quality, but no comprehensive definition of musical heaviness was developed. This article, therefore, elaborates a preliminary framework of musical heaviness by identifying its constituent production, performance, and compositional components, including their relationships. The findings suggest that while structural and performative components provide the necessary foundation for heaviness, metal has been increasingly driven by its production. Since musicians reach limits, technology has become one of the primary means to produce ever heavier metal music in the genre-defining quest for greater heaviness.


Introduction
Metal music has emerged in the last decade as a thriving research area within the interdisciplinary field of popular music studies. Building on earlier musicological (Berger; Walser) and sociological (Kahn-Harris; Weinstein) research, metal has increasingly been studied from various perspectives, from leisure (Spracklen) and Scandinavian (Helden) studies to history (Barratt-Peacock and Hagen) and gender studies (Hill). Much like its parent discipline of popular music studies, the field has undergone a "cultural turn," shifting the focus from the musical artifact to its broader functions for culture and society (Bennett). This trend toward multidisciplinary scholarship has added a more comprehensive perspective to our understanding of metal and its diverse cultures (Brown et al.; Wallach et al.). However, if research gives preference to a cultural lens over a "musical" one, the music is prone to be neglected (Arvidson; Tagg). 1 One musical area overlooked in metal studies is "heaviness," which for many researchers, notably from musicology and music technology, is the defining quality of the genre (Berger; Berger and Fales; Herbst, "Heaviness"; Mynett, Metal; Smialek; Thomas; Walther-Hansen; Williams). Despite a common appreciation of "heaviness" in metal music since its inception in the early 1970s, latterly accompanied by three decades of metal scholarship, no comprehensive definition or systematic understanding of musical heaviness exists. The term is taken for granted, based on the assumption that any metal researcher or fan knows what heaviness is. That the matter is far more complex quickly becomes evident when comparing the available academic sources, which vary in detail and often suggest that heaviness is a multifaceted metaphor (Walther-Hansen) encompassing more than just tonal qualities. Harris M. Berger notes that "any element of the musical sound can be heavy if it evokes power or any of the grimmer emotions" (59), and Mark Mynett sees heaviness as a "discursive category that implies a collection of sonic characteristics and performance/compositional approaches" ("Heaviness" 66). Simon Zagorski-Thomas similarly points out that while many musical qualities make metal "heavy," the perception of heaviness is intricate because it is affected by memories of live performances, band interviews, and album reviews (Musicology 215). Other influencing factors are visual qualities, such as corpse-paint make-up or gory album covers in extreme metal. From this perspective, the perceived heaviness of death or black metal bands is informed not only by the sound of their music (Halnon; Podoshen et al.), but also by extramusical extremity and transgression (Hannan; Kahn-Harris; Smialek).
"Heavy" semantically refers to something of great weight or power, indicating a high degree of physical mass or activity. This semantic understanding is consistent with musical "heaviness," described as an ontological metaphor existing at the base level of perception, with conceptual mapping employed to cognitively process an auditory experience for which no linguistic concepts exist (Walther-Hansen). Musical heaviness is commonly characterized by sonic weight, achieved through a distinctive low-frequency spectrum (Adlington; Hannan; Mynett, Metal; Thomas; Wallmark; Walther-Hansen; Williams), but it appears to be further affected by motion metaphors (Adlington) and force attributes (Walther-Hansen) that link heaviness with energy, power, and punch (Mynett, Metal). How the complex impression of heaviness is created by the interplay of structural features, performance attributes, and engineering approaches in record production is still unclear. Studies have looked at individual components in isolation, but a systematic understanding explaining what elements contribute to heaviness and how they relate to each other has not yet been established.
This article, therefore, aims to elaborate a framework of musical heaviness in the metal genre by identifying its constituent components and their relationships. Sociological, emotional, and associative components (e.g., Berger; Wallach et al.; Wallmark; Weinstein) are secondary. Extramusical factors (Halnon; Podoshen et al.) are disregarded, as is the low-fidelity aesthetic characteristic of some styles of black metal, which according to Ian Reyes (Sound, "Blacker") and Hagen is characterized by a very different form of heaviness. In the present research, such lo-fi aesthetics are not considered, as a specific and more detailed discussion is required, which is beyond the scope of this study.
The article is part of a larger research project that empirically investigates how heaviness is created and controlled in metal music production, building on Mynett's work ("Distortion," Metal, "Defining," "Heaviness," "Maximum") and other relevant studies in the formative research on the production of this genre (Herbst, "Historical"; Reyes, Sound; Thomas; Turner; Williams). The discursive metaphorical use of heaviness in metal is investigated elsewhere (Herbst and Mynett, "What"). Here, the focus is on musical production, performance, and compositional features that constitute and influence heaviness in recorded form.
To arrive at a preliminary but systematic framework of musical heaviness that reflects current discourse and establishes a common ground for future research, this study amalgamates varied considerations of "heaviness" in metal music literature and analyzes song examples. In this respect, any attempts to determine which musical parameters are deemed heaviest would appear somewhat futile, as a wide variety of heaviness "types" exist, and metal subgenres place certain qualities above others to distinguish themselves aesthetically, ideologically, and emotionally.
The findings suggest that while structural and performative components provide the necessary foundation for heaviness, this defining quality continues to be driven and informed by its production and the associated technology. This is especially the case, as it appears that metal musicians have reached the physical performance boundaries of tempi/speed of subdivisions while likewise reaching the realistic limits of down-tuning. Consequently, this study examines how the various structural and performative aspects relate to each other, enabling a range of rationalizations of how a desired effect of heaviness can be produced.

Sonic and Production Parameters of Heaviness
Given that most of the research on heaviness stems from music technology (Herbst, "Historical"; Mynett, Metal; Thomas; Wallmark; Williams), it is clear that a significant extent of perceived heaviness is directly informed by the music's associated production process. It may, therefore, come as a surprise that approaches to producing "heavy" sounds are seldom covered in mixing manuals (Man and Reiss). For Niall Thomas, the four key production elements of heaviness are impact, energy, precision, and extremity (187), while Mynett sees its core parameters in sonic weight, size, density, loudness, power, aggression, energy, emotion, and intensity (Metal 21). Based on academic and journalistic texts, this first section proposes and explains four interrelated conceptual parameters that play a role in shaping heaviness from a music production perspective. Structural and performative elements are subsequently considered based on the developed understanding of how they are influenced by production in the recorded format.

Distortion
Many scholars see the distorted electric guitar's sound as the defining element of metal music, not least because of its role for heaviness (Berger and Fales; Herbst, "Historical"; Kahn-Harris; Mynett, "Distortion"; Wallmark; Walser). Berger notes that "[f]irst and foremost, 'heavy' describes distorted guitar timbres" (58), further claiming that "all of the other uses of the term are metaphoric extensions of this primary use" (Berger and Fales 182). Guitar sounds have changed significantly over time (Herbst, "Historical"), facilitating the genre's quest for greater heaviness (Berger 58).
Distortion transforms the guitar from an impulsive to a sustained instrument, which is considered the main factor contributing to the perceptual experience of heaviness (Berger and Fales; Herbst, "Heaviness"). Harmonic distortion extends the guitar's highfrequency energy, expands the lower-and upper-frequency spectrum, shifts formants, flattens the dynamic envelope making it appear louder, and adds noise. The extended frequency spectrum provides a "weighty" low-end and ensures perceived "in-your-face" proximity and aggression due to the heightened high-end. But distortion is far from limited to the guitar. The bass guitar, snare drum, and drum rooms are also commonly distorted (Mynett, Metal), as are the vocals; either at source via the raspy, rough-timbred "singing" styles typical of metal (Wallach et al. 11; and/or through sound processing. Harmonic distortion is essential for metal music (production). Many core parameters of heaviness, such as perceived weight, size, density, loudness, power, and aggression, are supported by it (Mynett,. Engineering reasons aside, the human hearing system distorts when exposed to extreme sound levels. Furthermore, audible vocal distortion is produced when the capabilities of vocal cords are exceeded by shouting or screaming, usually caused by states of high-intensity emotion (Mynett,Wallmark 75;Walser 42). Hence right from an early age, distortion is associated with perceived loudness, power, aggression, energy, emotion, and intensity (Herbst, "Distortion"; Wallmark et al.).

Sonic Weight, Size, and Density
Weight is a fundamental component of heaviness, semantically and acoustically (Walther-Hansen 105-07). Sonic weight and heaviness are related but are distinguishable (Mynett,. The perceived heaviness of a single component and the whole production is strongly impacted by energy in the middle and upper parts of the spectrum. In contrast, sonic weight refers primarily to the low-frequency component and perceived "mass" of this frequency area, with little consideration of higher ranges of the spectrum (Gibson 119; Mynett Metal 14; Wallmark 67; Walther-Hansen 105-07). Deena Weinstein highlights the importance of the amplified bass guitar having a considerable impact on the sense of heaviness through weight, density, and depth (24). This spectral region is perceived as big, dense, and forceful when the bass plays together with the guitars and/or drums (Mynett,"Defining" 309). Similarly, double bass drums (aka double kick) add weight to a mix (Wallach et al. 11). Besides the mere presence of these instruments, their tonal characteristics are relevant. Since low frequencies contribute to the sense of weight, adjusting pitch is an effective way of controlling it Williams 52). The section from 0:02 to 0:34 in Meshuggah's "I Am Colossus" illustrates this effect with the palm-muted riffs played on a down-tuned eight-string guitar, accentuated by low-tuned kick drums and toms, further supported by the down-tuned bass. As Calder Hannan argues, the synchronized performance with sounds of low fundamental frequencies creates heaviness through reference to the physical world (443). Perceptually, these low frequencies are not just heard but physically felt (Wallmark 67), exaggerating the perception of "weight" (Mynett,"Heaviness" 74).
Most instruments in metal are typically performed, rather than programmed, so weight depends on specific performance qualities. If instrumental performances involve soft playing, sonic weight is not to be expected. Effective weight requires powerful, dynamic performance gestures that excite the lowest (and highest) frequencies possible on the given instrument. "Sonic weight" concerns both the quantity and quality of the lower spectral range and the associated level of energy required to generate these frequencies (Mynett,"Heaviness" 75), which low and high frequency equalizer boosts on a "soft" performance cannot fully provide (Mynett,"Heaviness" 68). With this in mind, we can note that every three takes during the recordings for Slipknot's .5: The Gray Chapter and every single take for Tool's Undertow drumheads were reportedly changed because they were hit hard (Massy 112).
The second particularity of metal music in terms of weight concerns the song tempo and resulting rhythmic subdivisions. Modern metal productions are the most effective when the low frequencies are controlled (Mynett,. There is no "one approach fits all" tactic because a production's low-frequency weight must be guided by the band's sounds and performance qualities. That is mainly due to variations in drum, bass, and guitar performance subdivision speeds, which give the low-frequency content of each instrument different amounts of space to expire within (Mynett,. If the slow wavelengths of lower frequencies have not had the opportunity to decay sufficiently before the subsequent transient, a resonant build-up of droning energy may occur. In addition to creating a boomy or muddy low-end, the resonant build-up can easily obscure the transients' mid-to-high frequency content. Consequently, faster performance subdivisions require more radical taming of the lower frequency content. A balance must be found between conveying the performance's energy through clarity provided by the high-frequency content and the extent to which low-frequency sonic weight contributes to the sound's perceived size (Mynett,. An example is the combined sonic weight of the kick, bass, and guitars on the Godthrymm track "We are the Dead (and Dreaming)." The long inter-onset intervals of the performances and the resulting available sonic space allow the production to emphasize sonic weight. There is restricted "clickiness" to the kick drum, while the sustain-based content of the bass is given considerable emphasis below 100 Hz, in line with the similar low-end weight emphasis of the kick, preventing the low-end of the production from being intermittent. This example can be contrasted with the production of Thy Art Is Murder's "Welcome to Oblivion," which features fast and tightly synchronized performance subdivisions that leave longer low-frequency wavelengths less space to decay within. Compared to the Godthrymm example, the production concentrates less on the sub-bass and low-end but emphasizes the upper bass region of 125-250 Hz (Mynett,. As related to sonic weight, perceived size is only one component of heaviness. The descriptor "heavy" indicates weight, and weighty objects generally have greater volume or size (Walther-Hansen). Berger notes that "[b]ass guitar timbres are heavy when they give the aural impression of great size" (58) and argues that boosting low-and high-end frequencies with an equalizer makes the recordings heavier by giving them power and tactile punch. By emphasizing the spectrum's upper and lower ends, the sound source's size or height is perceptually increased. Lateral positions in the virtual soundbox are determined by pitch and timbre so that the extremes of a sound's spectrum grow, metaphorically speaking, "larger than life" .
In the acoustic world, physical laws apply that allow us to obtain information about a sound source's perceived size. When hearing low frequencies, we usually associate these sounds as coming from larger, "heavier" objects. From an ecological perspective (Zagorski-Thomas, Musicology), a voluminous sound is automatically associated with larger sizes because lower frequencies generally require bigger entities able to generate this energy content. To give an example of linking such larger sizes to perceived slowness and resulting heaviness: Joel McIver considers "The Thing That Should Not Be" the heaviest song on Metallica's Master of Puppets album because of its sluggishness: "Very, very powerful, based on a slow, lurching, almost slimy riff that resembles some huge, wounded beast dragging itself along the sea bed, and boasts lyrics to match" (Justice 144). Comparing the heaviness of Master of Puppets and Slayer's Reign in Blood, McIver calls Metallica the winner because of the "crushing, intimidating or downright frightening atmosphere of the music" (Justice 149), created by sonic weight and great size.
As to size, the perceived performance environment's width and height dimensions play a key role (Moylan 176-80). Guitars and drum cymbals are usually panned wide in a metal mix, and sometimes psycho-acoustic measures are applied to make the sound appear even wider than the stereo field naturally allows. Such widening not only creates the impression of greater size but also heightens proximity to the listener. If a drum kit is heard from a distance, its width is relatively small, but going closer to the instrument increases the vertical and horizontal size . Such enhanced width and proximity add to aggression and contribute to heaviness because of the threatening nature of a close sound . Combined with intense high-frequency content, a widened sound source can even "seem closer than the loudspeaker it emanates from" (Zagorski-Thomas, "Musical" 141) and intrude into the listener's personal space (Moore 184-88) for a close "in-your-face" sound.
Density is another essential factor contributing to heaviness. It is partly related to sonic weight and size because bigger instruments with greater volumes are more likely to produce a denser sound than smaller instruments. In a metal production, density is mainly created from the thickening impact of harmonic distortion and realized by filling out the frequency spectrum (Walther-Hansen 100-07). The instruments in the virtual space must be positioned at different locations on the vertical and horizontal axes, with important components (mainly the kick, bass, guitar, and vocals) generally remaining in the foreground (Mynett, "Heaviness"). This strategy involves layering sounds, especially of the rhythm guitar (Herbst, "Historical").

Clarity and Punch
Metal music production is characterized by compromises. Maximizing all parameters rarely leads to a heavy sound because sonic weight and clarity must be balanced. Ron Vento emphasizes that "heaviness comes from smart tracking, low tuned instruments and clarity -not tons of low-end frequencies everywhere" (26). Sonic clarity enhances each sound's intensity and impact, reinforcing the energy of the rhythmical structures. Clarity is a valuable parameter for effective heaviness because it accentuates the energy of the performative gestures. It can be broken down into its two components "definition" and "intelligibility" (Mynett,. Definition refers to one particular instrument in isolation; intelligibility describes how easy it is to clearly hear the performance of an instrument in the context of an audio mix.
Definition is required for a single instrument's performance to be clearly understood. An example is the solo drum fill from 3:43 to 3:45 in Lamb of God's "Blacken the Cursed Sun," in which the individual drum instruments are decipherable despite the fast subdivisions. If the drums lacked definition because of a dull attack and resonant sustain, it would be harder for the listener to understand this fill. Without definition, its impact would be largely lost, as would the drummer's musical intentions.
Intelligibility, on the other hand, refers to how difficult it is to clearly identify an instrument's performance in the context of a mix. For instance, the tremolo-picked guitar riff between 0:09 and 0:24 in Insomnium's "Valediction" is supported by a fast double kick drum and tom fills, which are rhythmically synchronized with the bass. Despite the sonic density and structural complexity, the pitch and rhythmic qualities of the guitar riff stay intelligible. The performance approach of an artist hence informs the necessary level of intelligibility. Slower, groove-based performances can be comprehended with less intelligibility, whereas fast or rhythmically complex performances benefit from a greater focus on intelligibility. Artists placing less emphasis on performance complexity in favor of greater sonic weight need to place less emphasis on clarity, while the opposite would be the case for artists who perform fast and complex structures (Mynett,"Maximum" 299).
Clarity depends on sufficiently captured transient detail. One might expect power primarily to result from sonic weight, but for present and hard sounds that generate much of a metal production's energy and excitement, upper-mid and high-frequency -transient information is required (Thomas 193) to provide the necessary "force" qualities (Walther-Hansen 105-107). Transients are crucial for "punch," a semantic descriptor as vague as "heaviness." Research on punch is still in its infancy, but transient energy seems to be the decisive factor (Fenton and Lee). "Punchy" sounds are characterized by a burst of energy and spectral density that cause a spike in volume. This burst changes the dynamic power in the spectrum and emphasizes the waveform's attack/transient components in relation to the sustain and decay phases (Mynett,Metal 16). Although all instruments are potentially punchy in a metal production, the term most often refers to the drums, whose "punchiness" is amplified through drum sample augmentation and audio processing to cut through the dense wall of guitars (Herbst and Mynett,. The shaping of punch must be informed by the subdivisions' speed (Mynett,. Sound sources of considerable size and weight take up a greater amount of sonic space. If this space is unavailable due to fast subdivisions, the source's size and weight are perceived as excessive because the performance's energy and intensity are obscured, and the clarity of other elements is diminished. In drum performances that feature fast subdivisions, "punch" is therefore placed above size and weight. An example is Dimmu Borgir's "The Unveiling," where the drums have a sharp attack, fast decay, and are relatively "thin" with minimal sonic weight, especially the kick drums. This aesthetic contrasts with the bigger drum sound in My Dying Bride's "Your Broken Shore," which emphasizes sonic weight and size, enabled by the greater available space for these attributes (Mynett,"Distortion" 79).
The relationship between heaviness and punch is complex. While heaviness may be more of a timbral and punch a temporal feature, timbral quality cannot be separated from the temporal envelope, just as temporal characteristics cannot be detached from timbre. The Dimmu Borgir and My Dying Bride examples show how punch is related to timbre and the spectral space available in the mix. Similarly, heaviness usually depends on punch (Walther-Hansen 105-07). Only in slow subgenres like doom or drone can heaviness function through sonic weight alone with little punch. One such example is Sunn O)))'s album Pyroclasts, which only consists of very distorted guitars, bass, and synthesizers without any percussive instruments. All guitar and bass attacks are obscured, preventing the production from having any significant punch. The dense wall of distortion, a purely timbral quality, may nevertheless be perceived as heavy.

Loudness and Extremity
High volume is a common descriptor for the sound of metal (Wallmark; Walser; Weinstein; Williams). Volume can support other parameters such as sonic density, particularly when compression condenses the arrangement's dynamic range (Mynett,"Distortion";Williams;Musicology 214). Great perceived volume can also create impressions of power and excitement (Wallach et al.; Williams). For translating the same impression of power and intensity to lower listening levels, the low and high frequencies are boosted so that the sound is psycho-acoustically perceived as louder and more powerful (Wallmark 70) because the auditory system is significantly more sensitive to high and low frequencies the louder the signal becomes (Senior 62). An increased degree of excitation exerted on a snare drum or guitar also correlates with increased production of high-frequency energy at the gestural level. Increased low-frequency energy is similarly associated with sounds produced through high-energy impact (Mynett,"Heaviness" 75). That is why boosting high and low frequencies can support the impression of aggressively played instruments.
Extremity is another component noted in connection with metal productions (Turner). It does not describe musical qualities but characterizes an approach to writing, performing, and producing music. Keith Kahn-Harris (29) points out that extremity is ubiquitous and vague, yet it implies the transgression of boundaries. Extremity is accepted in metal production as an ideal achieved through "extreme" sound processing (Thomas and King; Turner). Accepted audio engineering standards, characterized by moderate processing and corrective equalization cuts instead of creative boosts, are largely ignored. As Roey Izhaki notes, "[I]n genres such as death metal, equalizers are often used on what is considered a radical way, with very generous boosts. The equalizer's artifacts are used to produce harshness, which works well in the context of the specific music" (231). Moreover, guitars and basses are down-tuned in many modern metal genres, and guitars with additional lower strings are played, as heard in Ring of Saturn's "The Husk," performed on a ninestring guitar. Extremity can be a production ideal in its own right (Turner), even if serving to achieve other essential parameters of heaviness like sonic weight (Williams).

Structural and Performative Features of Heaviness
Metal has diversified into multiple subgenres in its over fifty-year history. It would be tempting to regard extreme metal (Kahn-Harris) as heavier than mainstream metal. Yet, such music can also be heavy when it emphasizes the right features structurally and sonically. An example of mainstream metal performed as fast as extreme metal is "The Game" by power metal band DragonForce that, by sonically featuring clarity over weight, can be directly contrasted with a weight-focused production, such as heard in "Molten Black Earth" of the death-doom metal band Asphyx. Rather than providing a stylistically comprehensive analysis of metal, the following considerations will highlight structural and performative features influencing the perception of heaviness.

Speed
In the quest for heaviness, various metal subgenres have explored the two extremes of slowness and fastness and the combination of different feels. Many metal songs contain slow sections as a contrast to the generally high tempo. These slow sections are sometimes brief transitions; others are dedicated breakdowns. Breakdowns have become common through the spread of death metal and are designed as "mosh parts" (Pillsbury 10). Lewis Kennedy discusses three kinds of "slow and heavy riffs" -the slowdown, slam, and breakdown -with the "breakdown" being the umbrella term (88-89). The "slowdown" is typical of early American death metal and characterized by a sudden drop in tempo, along with a shift from palm-muted to open guitar picking patterns. An example is Cannibal Corpse's "Hammer Smashed Face," which transitions from fast riffing into a slowdown section between 0:46 and 1:17.
"Breakdowns" are similar to slowdowns and cannot always be distinguished. A defining characteristic is a half-time drumbeat. The cymbals underline the new pulse, and the kick drum accentuates the bass and guitar rhythm. The guitar patterns are played with either open or palm-muted picking and tend to be more complex than in a slowdown. A breakdown can be heard in Oceano's "The Taken" from 0:50 to 1:20. The "slam" does not require a tempo drop and is characterized by chromatic, palm-muted chord progressions, as in Katalepsy's "Lurking in the Depth" (0:52-1:08). Eric Smialek argues that breakdown sections "add to the overall impression of weight and heaviness" by emphasizing low frequencies, accentuated by the drums and palm-muted guitars, and by creating a more sluggish feel (230). The slower gestures combined with low pitches may be interpreted as metaphorically increased weight (Walther-Hansen 105-07). It cannot be objectively determined whether the breakdown is heavier than the rest of the song, but the contrast from fast to slow and back probably contributes to the perception of heaviness as much as the breakdown itself. This contrast involves a shift from performance and note complexity to sound and timbre (Pieslak 46), or sonically speaking, from clarity to sonic weight.
The psychological experience of the breakdown in the metal genre may be interpreted as the equivalent of the drop in electronic dance music. As Ragnhild Torvanger Solberg explains, the EDM listener's emotional experience is typically manipulated and intensified by creating contrasts between the build-up and drop. During the build-up, the frequency spectrum is thinned out by removing the bass and kick drum. Uplifters, a frequency-filtered wall of noise, create an upward motion. This state of tension and anticipation dissolves with the drop, where kick and bass return, the frequency spectrum widens, and the production emphasizes rhythmic groove and sonic weight, resulting in a downward motion. In metal music, there is typically no build-up to the breakdown, as the breakdown is merely the contrast to the faster form parts. The effect is nevertheless like the EDM drop. The sudden emphasis on rhythm, accentuated by all instruments and played in a low register, releases tension from the fast subdivisions and allows larger physical gestures in the mosh pit. Maintaining heaviness throughout the song's length can be achieved by changing the tempo and feel in conjunction with shifting production from clarity to sonic weight and vice versa with various alternating forms of heaviness.
Subgenres like doom metal rarely drastically change feels and tend to stay within a limited range of slow tempi. The primary means for creating heaviness are slow subdivisions, low-tuned instruments, and excessive distortion, collectively maximizing sonic weight. The rhythmic complexity of other metal genres is simplified with guitars playing sustained power chords for a wall of distortion rather than fast palm-muted single-note lines. Electric Wizard's "Funeralopolis" is an example of this slow, grinding form of heaviness.
The quest for greater speed is more common than exploring slowness for heaviness. Early hard rock and heavy metal bands experimented with fast songs: Deep Purple's (1970) "Speed King," Motörhead's "Overkill," Venom's "Witching Hour," Accept's "Fast as a Shark." According to McIver, Abaddon (Tony Bray) popularized what became the essence of thrash metal and the foundation of extreme metal: the double-speed snare drum pattern, first recorded on Venom's "Witching Hour" (Justice 51-52). Songs like these led to the notion that faster equals better. Early thrash metal bands in the USA and Europe explored the effect of ever-faster speeds, resulting in new forms of heaviness. Slayer vocalist Tom Araya once stated, "[T]he heaviness wasn't there until we came around -the same with Metallica, Anthrax, Exodus, and us. I think we've had a big impact on the sound. We took music and made it really heavy" (Brown 68). Araya refers to the pursuit of speed as the primary mechanism for achieving heaviness, carried out competitively, as the biographies of Metallica (McIver, Justice) and Slayer (McIver, Bloody) suggest. A highlight in speed was Slayer's "Necrophobic," with 248 beats per minute (bpm). Tempi have generally gone up since then. According to Kahn-Harris (32), tempi in modern metal often sit between 150 and 250 bpm. The fact that metal productions have become faster on average over time might suggest that high tempi -in terms of beats per minute -are crucial to the identity of many extreme metal bands. However, this view does not consider that the underlying tempo is less important for the perception of speed than the way it is divided into its rhythmic subdivisions, with faster subdivisions being more effective than a mere increase in bpm. For example, Accept's "Fast as a Shark" features eighth-note double kick patterns at a tempo of 280 bpm, yet its perceived speed is slower than the 200 bpm of Kreator's "Pleasure to Kill," which consists of sixteenth-note subdivisions.

Rhythm
The drumbeat is one of the determining elements affecting the perception of speed. The snare and cymbals set the overall feel; the kick is relatively independent of the snare and the drum kit's overall feel. Even if the tempo is slow, the kick can have fast bursts played. Such phrasing makes the kick an essential part of the overall groove and an expressive instrument supporting and augmenting the rest of the ensemble.
The double bass has been used in rock since the 1960s by the drummers of Cream, the Who, and Rush (Nyman). Metal drummer Phil Taylor of Motörhead was influential in using the double kick technique in the late 1970s (Cope 99), inspiring the wave of speed and thrash metal in the 1980s, the decade it became one of metal's central stylistic features. It is sometimes played in bursts for accentuation, other times as a constant bed of low-end on which the other instrumentalists can perform.
There are three standard double bass patterns differing only in the snare placement ( Figure 1). According to Necrophagist drummer Hannes Grossmann, the backbeat pattern feels the slowest and "has a somewhat 'heavier' vibe to it" (156).
More standard rhythms contributing to a sense of acceleration and speed, aggressiveness, and heaviness exist in extreme metal (Grossmann 81;Phillipov 86). The "blast beat" is a drumming technique that plays a key role in creating intensity through fast snare hits. Ross Hagen describes it as one of the "most idiomatic rhythmic devices in black metal" that sonically resembles a "prolonged burst of machine-gun fire" and a "sort of sonic blast" (186). Blast beats are used differently within the various metal subgenres. For example, all instruments in death metal have similar subdivisions and perception of speed compared to black metal, where the drums normally play faster subdivisions than the other instruments, creating an atmospheric rather than a rhythmic impression (Hagen 186).
The blast beat is essentially a double-time "skank beat" (Figure 2), from which it initially developed. It was performed by early thrash metal bands like Slayer, Metallica, and Kreator, and extreme metal bands like At the Gates, as in "Slaughter of the Soul." In early extreme metal, the blast beat was primarily used as an effect for noise and frantic energy rather than a groove concept (Grossmann 200). Three main blast beat concepts exist that differ less in their drumming than how drums relate to the overall arrangement (Levi). The first is the "groove approach," as heard in Thy Art Is Murder's "Make America Hate Again." Between 0:28 and 0:46, the blast beat provides an alternative beat to the guitar riff that builds up tension, which is released by changing to a standard double bass pattern while the guitar riff remains unchanged. The second is "technical riff outlining," typical of Black Dahlia Murder and Necrophagist. It can be heard in Black Dahlia Murder's "Everything Went Black," where the blast beat accentuates the single-note guitar lines between 0:22 and 0:30. The third is the "wall of sound approach," typical of symphonic black metal bands. Between 1:02 and 1:18 in Dimmu Borgir's "Kings of the Carnival Creation," the high speed of the blast beat produces a sonic density that complements the otherwise relatively thin guitar playing open tremolo-picked notes on the higher strings. Regardless of the concept, blast beats create heaviness through rhythmic and sonic density and by augmenting or complementing the guitar riff. Like in breakdowns, the contrast between blast and regular double bass beats creates tension and release to maintain a heavy feel throughout a song.
Aside from these groove concepts relative to the arrangement, there are several established blast beat styles. The "hammer blast" (Figure 3) creates a raw and "brutal death metal sound" (Grossmann 221), as in Suffocation's "Liege of Inveracity." If the hammer blast is played with a double-time kick (Figure 4), the beat is commonly referred to as a "bomb blast" (Grossmann 228). The binary version of this drumbeat can be heard in Cryptopsy's "Graves of the Fathers," the triplet variation in Cannibal Corpse's "The Strangulation Chair." The bomb blast played with the snare accentuating all sixteenth note kick drum hits is called "gravity blast" and is characteristic of Origin, Beneath the Massacre, and Defeated Sanity (Grossmann 236).
The regular blast beat (Figure 2) is referred to as the "Euro blast beat" (Levi; Phillipov 86) because it has historically been more common in Europe. The hammer and bomb blast beats are typical of US-American death metal, also known as "brutal" death metal (Smialek 120). Just like heaviness, "brutal" is no clearly defined musical descriptor but tends to be used for bands considered "heavy." Based on the rhythmic differences between the European and American blast beats, it seems that the rawness of all drum instruments emphasizing the same subdivisions evokes associations of brutality in the death metal genre.
Drum patterns are relative to the guitar riff and often follow it (Mynett,"Defining" 299). The kick frequently plays the same subdivision as the guitar and bass to achieve maximum rhythmic and sonic impact, as the kick adds clear attack transients and low-frequency energy to the harmonic instruments. Precise ensemble    synchronization is essential for heaviness because if drum patterns coordinate the metric structures of guitar and bass, this collective performance lends the music a dense texture and punch (Fenton and Lee). The effect of ultimate ensemble rhythmic synchronization can be heard in Machine Head's "Imperium." The part from 1:12 to 1:25 features synchronization of all instruments for maximum impact, characterized by high spectral density and precise rhythmic accentuation (see Figure 5).
When synchronized instrument parts do not achieve the required level of precision, the ensemble performance is typically perceived as subjectively less heavy than a production featuring tight synchronization (Mynett, "Defining," "Maximum").
Ensemble synchronization with clear rhythmic subdivisions can create heaviness, but conversely, rhythmic difficulty may also contribute to heaviness. Analyzing Meshuggah's "I Am Colossus" and the Dillinger Escape Plan's "Prancer," Hannan argues, While rhythmic difficulty is neither necessary nor sufficient for heaviness, it can effectively contribute to it in a variety of ways: by allowing an opportunity for a band to showcase their precise playing and inspire awe; and by being perceptually unwieldy, awkward and uncomfortable, rhythmically difficulty structures mimic common attributes of heavy physical objects. By innovating in their use of rhythm, bands claim transgressive subcultural capital and their music becomes serious and therefore heavy. (455) Hannan's considerations suggest that the perception of heaviness is partly associative and that associations can be influenced by musical structures, performance qualities, and the listener's ability to appreciate these.
Ensemble rhythmic synchronization is more important in extreme metal than in traditional heavy metal (Mynett, "Defining" 300-01), prioritizing rhythm over harmony. Even bands not striving for performance speed typically concentrate on rhythm. Historically, faster tempi and subdivisions led to a shift on the guitar from power chords toward fast single-note lines that exploited the "rhythmic potential of repeated pitches" (Pillsbury 129). When the same pitch is played repeatedly, faster subdivisions can be achieved. With palm-muting, the guitarist muffles the sound by carefully placing the palm of their hand on the strings near the guitar's bridge. This dampening shortens Figure 5. Section of Machine Head's "Imperium". sustain, enhances the performance's rhythmic characteristics (Herbst, "Shredding"), and generates a "heavier sound" (Smialek 94). Similarly, shifting from open to palm-muted picking creates variation and sustains interest, and changes the sonic texture and rhythmicity of a form part, which may be perceived as heavy through contrast. This shift is effective both in riffs that only change accentuation and in separate riffs, one of which is played open and one with palm-muting. An example of the latter is the part from 6:20 to 7:06 in Gojira's "Flying Whales."

Harmony
Dissonance is nothing new in the history of metal music. The tritone interval has been used since the genre's inception, as in Black Sabbath's self-titled song on their debut album Black Sabbath. The use of modality, especially darker and dissonant modes like Phrygian and Locrian (Kahn-Harris 31; Walser 46), is common in many metal subgenres. These modes have a bearing on the music's atmosphere, but it is unclear whether they also affect the perception of heaviness. There are yet indications that harmony may influence heaviness. Berger suggests that atonality can evoke the impression of heaviness because it defies the listener's tonal expectations (63). Hence breaking up with the minor tonality favoring a more obscured tonal center may be understood as a step toward greater heaviness (58). If clear and repeating parts are missing, the song is less memorable because it is hard to grasp its structure. Like rhythmic difficulty potentially contributing to heaviness (Hannan), structural and harmonic complexity and the resulting lack of catchiness may also be linked to it. An example of structural complexity with many form parts and few repetitions is Carcass's "Symposium of Sickness," which claims a heavy aesthetic.
One of the few metal subgenres that commonly adds full chords to the standard repertoire of single-note lines and power chords is black metal. While the major chord with high guitar distortion levels is still relatively consonant (Herbst, "Heaviness"), the minor chord is essential for black metal's dissonant and abrasive aesthetic (Hagen). The chord's performance with tremolo picking, typically played without palm-muting, creates a droning quality, reduces rhythmic clarity, and increases the dissonant impression due to the detuning caused by the constant state of wide vibration (Hagen 187). Even though abrasive sounds add to dissonance created by the distorted minor chord (Herbst, "Heaviness"), how dissonance relates to heaviness is still unclear. Considering that metal strives for greater heaviness but not necessarily increased dissonance (Herbst, "Heaviness"), the two concepts seem related but different.

Vocals
Traditional heavy metal has featured melodic vocals and popular tenor singers like Rob Halford, Bruce Dickinson, or Michael Kiske. Contemporary extreme metal styles have shifted musically from melody to ensemble rhythmic complexity (Mynett, "Defining"). This altered focus changed the role of the vocals in that broad equivalence to the reduced melody of the instruments can be noted. However, vocal styles often determine metal subgenres (Hagen; Kennedy; Phillipov; Purcell), although not as clearly as in the 1990s and 2000s when subgenres did not mix as much as they do today (Hillier).
The high and clear voice of traditional metal embodies "power" but contributes less to perceived heaviness. In contrast, the screams, shouts, snarls, barks, roars, grunts, and growls of extreme metal enable transgression (Kahn-Harris). Vocals with these characteristic attributes are more likely to be perceived as heavy, especially with the general tendency toward lowering the pitch range in growl-like styles to maximize metaphorical weight. Regardless of the technique, extreme metal's vocal sounds tend to be noisy with non-harmonic components, which sonically resemble distorted guitar timbres (Kennedy 75). Berger claims that such vocal styles "can be referred to as heavy" (58) and that the less discernible the pitch is, the heavier the impression will be. The acoustic analogy between guitar distortion and extreme metal vocals has been challenged. It has been argued that such vocals either lack a fundamental pitch (Mesiä and Ribaldini) or have a fundamental pitch but otherwise an inharmonic overtone spectrum (Wallmark 73).
Smialek suggests that extreme metal vocal styles can be characterized as "complexpitched" (260), meaning that brighter and darker timbres can be distinguished without relating them to a single pitch, as is possible with drum cymbals.
Despite the differences in pitch between the distorted guitar and extreme vocals, several authors explain the vocals' perceptual effects compared to guitar distortion. Such an association may be more metaphorical than a direct acoustic correlate. Michelle Phillipov (74) sees the death metal growl as an imitation of the down-tuned guitar, whereas Mynett ("Distortion" 77) considers the vocal's distorted impression resulting from physical exertion beyond the limits of normal articulation, not unlike guitar distortion caused by overloading the amplification system (Berger and Fales). The evidence is inconclusive overall, but there appears to be a high acoustic resemblance between vocal timbres and guitar distortion, at least for growl-like vocal styles. Chen-Gia Tsai et al. find that growled vocals contain more inharmonic components distributed among adjacent harmonics occupying larger frequency areas in the spectrum than would be the case with clean singing (Thomas 132). Accordingly, extreme vocal techniques expand the vocals, just as distortion extends the guitar's frequency spectrum. Such extensions make the guitar and vocals appear larger, which may metaphorically be perceived as heavier.
For achieving an aggressive and heavy sound, the main approach in extreme metal is distorting the vocals in the low or high register through articulation and audio processing. The pronunciation may additionally influence the perception of heaviness. Smialek proposes that lowering the first two formants when articulating vowels can make the expression appear heavier: If a vowel such as /u/ (as in "who") has the lowest recognizable first and second formant frequencies of vowels in American English, a death metal vocalist could sacrifice the intelligibility of a vowel such as the /ʌ/ in "blood" so that it can instead sound lower and thus heavier: /blʌd/ becomes /blud/. (Smialek 269, Based on spectrographic analysis of Morbid Angel's "He Who Sleeps," Smialek argues that some death metal vocalists alter the vocal by lowering the formants when articulating short words and modulating brighter vowels to darker ones for longer words because this produces a heavier sound (276). The principle behind this line of reasoning resembles that of down-tuned guitars and low-tuned drums; lower-pitched notes produce metaphorical weight, one of the main components of heaviness.

Discussion and Conclusion
More than two decades ago, heaviness was declared the central feature defining the metal genre. Berger noted that "[m]etal history is most often summed up by metalheads as a progressive quest for ever-heavier music. A rich and complex concept differentially interpreted across scenes, 'heavy' refers to a variety of textural, structural, and affective aspects of musical sound and is crucial for any understanding of metal" (58). Heaviness is still a relatively unexplored phenomenon, despite its role within the genre. By amalgamating ideas about heaviness discussed in varied sources and extending them through musical analyses, this study set out to work toward a systematic framework of musical heaviness that identifies its constituent components and their relationships. Due to the complexity of acoustic, perceptual, musical, and performative parameters and their interplay, besides the wide variety of subgenres existing in metal (Hillier), the preliminary framework must inevitably be introduced in a reductionistic form. The analysis did not expand on how heaviness is typically constituted in each subgenre but instead outlined the main musical features that contribute to heaviness. It explained how interaction occurs between the various production, composition, and performance components, each dependent on and reinforcing the other. Future research may refine and apply this framework to study and compare the heaviness of specific subgenres.
The preliminary framework might be misunderstood as placing production above structure and performance. This is not the case because production can only enhance the musical composition realized through performance. Mynett suggests that "metal is the least acceptable when delivered with poor production, as the music's defining quality 'heaviness' will inevitably be vastly compromised" ("Distortion" 68). This crucial role of production is supported by the fact that most research on heaviness emanates from music technology (Herbst, "Historical"; Thomas; Wallmark; Williams) or at least considers it necessary (Kennedy; Smialek; Walser).
Modern metal productions rarely attempt to simulate a believable acoustic performance environment; they create their own highly effective reality (Mynett,"Heaviness" 73). Unlike productions of the 1970s to 1990s that sought to achieve performance authenticity, contemporary productions exaggerate detail and size to create a "larger than life" impression (Mynett, "Heaviness" 71). Production has moved "away from traditional, performance-focused, recording, toward a more fragmented, technologically architectural approach" that relies on "innovative processing and architectural approaches to recording, and mixing, the instrumental elements of the genre" (Thomas and King 499). Compositions have become more diverse, speed has increased, performance quality improved, and -partly enabled by more powerful digital music production tools -the resulting sound has become bigger, weightier, and clearer. This points to the genre's considerably enhanced heaviness being largely informed by the ever-more extreme, radical, and -dependent on one's point of view -unrealistic production of the music (Thomas and King 501). This trend has brought a rise in the programming of drums, bass, and lead guitar (Herbst and Mynett, "Nail"), making composition and performance a "product" of the production. Zachary Wallmark's analysis of death metal sees extremity at the center of its aesthetics and appeal. He highlights all areas of performance, composition, and production, motivated by the pursuit of ever-greater heights of extremity (Kahn-Harris), much like metal's general quest for greater heaviness (Berger and Fales). Concerning the role of technology, Wallmark interestingly concludes that this need for transgression "has led us to the proverbial brink: human bodies are becoming inadequate to the task, and machines are used as a substitute," citing "inhumanly fast" (81) drumming as an example of extremity afforded by advances in music technology. Wallmark goes on to explain: It could be argued that bodily, material limits have been reached in the death metal scene, but this in itself does not augur the end to this teleological pattern, at least not yet. In the arms race of extreme in death metal, human bodies have been aided and abetted by various technologies to expand the limits of possibility: formerly unsurpassable boundaries are, with computer manipulation, suddenly available to us. . . . with the help of technology, what we hear in death metal is vastly different from the reality of its physical production. (76)(77) Since musicians have reached the limits of tempo and low-tuning instruments, technology seems most promising to continue metal's quest for "greater X" (Berger and Fales 193), which may be heaviness, extremity, aggression, brutality, evilness, or any other desired attribute in the diverse subgenres of metal. When or if even technology reaches its limits is difficult to determine. However, this question is seldom asked when considering heaviness in metal music and goes beyond the scope of this article.
Establishing a comprehensive definition of musical heaviness with fixed weightings for the contributions of individual productional, performative, and compositional features is similarly challenging. Firstly, contrary to the often-assumed universal understanding in the metal genre, heaviness is shaped by subgenre conventions and subjective factors, not least those outside the music, be they emotional, associative, or ideological (Herbst and Mynett, "What"). Secondly, heaviness is relative to time and other releases. Much of the music once considered heavy can no longer be called so a few years later . Thirdly, the few existing empirical studies agree that the perception of heaviness differs between fans and non-fans and probably also between listeners of metal's various subgenres (Berger; Czedik-Eysenberg et al.; Herbst, "Heaviness," "Distortion"). For those not fans of the genre, hearing distorted guitar tones, extreme vocals, or aggressive high-speed drumming may be enough to let them perceive the music as heavy (Herbst, "Heaviness"). On the other hand, metalheads might argue that metalcore's aggressiveness through screamed vocals and rhythmically complex ensemble performances is heavier than that of the historically older death metal style with its grunts and deep timbres. Relevant qualities such as aggression, punch, power, rawness, evilness, and brutality play a role in the perception of heaviness. These features may even be components of metal's heaviness, according to recent research (Herbst and Mynett, "What"), where specific musical attributes are emphasized, including: "thickness" with rich layers of sound; "fatness" with heightened low-end spectrum; "fullness" with pronounced overtones; associative attributes like "darkness," achieved by attenuated high frequencies, with genre-specific connotations such as sadness, evilness, or mysteriousness (Wallmark; Walther-Hansen 98-100).
Several types of heaviness exist, and metal subgenres prioritize certain qualities over others to distinguish themselves aesthetically, ideologically, and emotionally. Hence any attempt to definitively determine which musical parameters are the heaviest or most extreme, brutal, or evil, appears futile. Examining how the various structural, performative, and technological components relate to each other to achieve the desired effect of