Theory & Background

Research Overview

This interactive lab demonstrates findings from two psychoacoustic studies investigating how metal music production techniques shape the perception of "heaviness." Using a "one song, many mixes" methodology, we commissioned nine internationally recognized metal producers to independently mix the same original recording. This approach captured real-world professional practices while maintaining experimental control for systematic analysis.

We then conducted listening experiments with 79 participants, who rated perceived heaviness alongside other perceptual attributes. By correlating these ratings with acoustic measurements extracted from the mixes, we established quantitative relationships between production choices and perceived heaviness.

Heaviness in Metal Music Production

Heaviness is a defining aesthetic in metal music, yet it has resisted empirical investigation. The term describes both slow, weighty passages and fast, aggressive sections, seemingly contradictory musical approaches. Our research reveals that despite this complexity, heaviness perception is anchored in specific, measurable acoustic properties.

We approach heaviness through two complementary frameworks. Ecological perception (Gibson, 1979; Clarke, 2005) suggests that listeners directly perceive invariant acoustic properties in the sound that specify qualities of the source, like a massive, dense object or a forceful impact. Embodied cognition (Lakoff & Johnson, 1999) explains how listeners make sense of these acoustic cues through conceptual metaphors, understanding abstract musical qualities in terms of concrete physical experiences like weight, force, and density.

Acoustic Hardness: The Primary Driver

We quantified the acoustic properties of each mix using the "hardness model" developed by Czedik-Eysenberg and colleagues (2017, 2024). This validated model measures seven spectral and tonal features, with the strongest predictors being:

• Spectral complexity: The number of peaks in the frequency spectrum: higher complexity creates a denser sound
• Reduced spectral contrast (1.6–3.2 kHz): A "filled-in" upper-midrange that creates a cohesive "wall of sound"
• Dissonance: Sensory roughness from clashing frequencies
• HPCP entropy: Tonal ambiguity, indicating departure from simple harmonic structures

Our central finding: acoustic hardness strongly predicts perceived heaviness (r=.775, p<.001), explaining 60.1% of the variance in listener ratings. This correlation remained robust even when comparing mixes of the same musical section, demonstrating that producers can systematically control perceived heaviness through mixing techniques alone.

The two producers in our "High Hardness" cluster (Buster Odeholm and Dave Otero) achieved significantly higher heaviness ratings by maximizing spectral complexity and reducing upper-midrange contrast. This creates what Zagorski-Thomas (2014) calls a "sonic cartoon" that exaggerates acoustic cues for overwhelming weight and power.

Perceptual Punch: A Secondary Contributor

We also measured acoustic punch using the PM95 model (Fenton & Lee, 2019), which quantifies the transient impact of percussive sounds like drum hits. This model isolates fast-onset transients and calculates their perceptually weighted loudness, primarily in lower frequency bands.

Surprisingly, while listeners' subjective ratings of punch correlated strongly with heaviness (r=.761), the acoustic punch model did not significantly predict heaviness in a multiple regression once hardness was accounted for (β=.220, p=.210). Even more striking: the acoustic punch model failed to correlate with listeners' subjective punch ratings (r=.415, p=.087).

We interpret this disconnect as evidence that in dense, spectrally saturated metal mixes, the overwhelming textural "wall of sound" masks or recalibrates what listeners perceive as "impact." The sustained, massive acoustic presence dominates the perceptual experience, making discrete transient events less salient than they would be in sparser musical contexts.

Asymmetrical Conceptual Blend

These findings led us to propose a refined model of heaviness as an asymmetrical conceptual blend. Heaviness emerges from two conceptual inputs:

• "Mass & Texture" afforded by acoustic hardness: the perceptual anchor
• "Force & Impact" afforded by punch: a secondary contributor

The hardness dimension provides the foundational experience of spectral density and sonic weight, while punch adds percussive force that is interpreted within the context of that textural mass. Cognitively, listeners must first perceive "an object with mass" before making sense of "forceful actions upon it."

This hierarchy explains the production trade-offs evident in our data. Techniques that maximize hardness, such as heavy compression, saturation, spectral saturation, inherently reduce dynamic range and can "smear" the sharp transients responsible for punch. Our findings suggest that while metal performances increasingly foreground rhythmic precision, the listener's holistic perception of heaviness remains anchored in the textural "wall of sound."

Two Forms of Heaviness

Analysis of our two contrasting musical sections revealed that while some acoustic features are foundational to all heaviness, others are context-dependent:

• Section 1 (Fast, Intensive): High textural density from tremolo picking and blast beats. Heaviness driven primarily by spectral complexity and reduced upper-midrange contrast; dissonance was not a significant correlate.
• Section 2 (Slow, Anthemic): Emphasis on sonic weight through low frequencies and rhythmic space. Heaviness driven by the same core predictors plus a very strong contribution from dissonance (r=.89).

Both approaches create heaviness, but through different combinations of acoustic cues. This suggests that "heavy" encompasses multiple valid aesthetic strategies within metal production.

Key Publications

This research is detailed in two articles currently under peer review:

• Herbst, J-P., Mynett, M., Fenton, S., Czedik-Eysenberg, I., Smialek, E., & Reuter, C. (under review). "Hard and Heavy: A Perceptual Study of Acoustic Hardness and Heaviness Aesthetics in Metal Music Production." Music Perception.
• Herbst, J-P., Mynett, M., Fenton, S., Czedik-Eysenberg, I., Smialek, E., & Reuter, C. (under review). "Musical Heaviness as a Conceptual Blend: The Asymmetrical Roles of Textural Hardness and Temporal Punch." Psychology of Music.

Key Supporting References

• Clarke, E. (2005). Ways of Listening. Oxford University Press.
• Czedik-Eysenberg, I., Knauf, D., & Reuter, C. (2017). "'Hardness' as a Semantic Audio Descriptor for Music Using Automatic Feature Extraction." Informatik 2017 (pp. 101–110).
• Czedik-Eysenberg, I., Wieczorek, O., Flexer, A., & Reuter, C. (2024). "Charting the Universe of Metal Music Lyrics and Analyzing Their Relation to Perceived Audio Hardness." Transactions of the International Society for Music Information Retrieval, 7(1), 129–143.
• Fenton, S., & Lee, H. (2019). "A Perceptual Model of 'Punch' Based on Weighted Transient Loudness." Journal of the Audio Engineering Society, 67(6), 429–439.
• Gibson, J. (1979/2015). The Ecological Approach to Visual Perception. Psychology Press.
• Lakoff, G., & Johnson, M. (1999). Philosophy in the Flesh. Basic Books.
• Zagorski-Thomas, S. (2014). The Musicology of Record Production. Cambridge University Press.