Research Methodology

The Song: "In Solitude"

The HiMMP research team composed and recorded an original metal song titled "In Solitude" specifically for this project. Drawing inspiration from the COVID-19 pandemic, particularly the atmosphere and isolation of the initial UK lockdown, the lyrics explore themes of solitude, inner reflection, and finding meaning amid external chaos. The song encourages retreat from psychological stress to seek inner peace, with emotional contrasts ranging from expressions of depression and social isolation to more uplifting moments.

Musically, "In Solitude" blends elements from various metal subgenres, including heavy metal, melodic death metal, and black metal, while featuring varying rhythmic subdivisions and tempos. The song follows a compound AABA form, the most common structure in metal ,with verse-chorus groups alternating with an extended breakdown section that provides dramatic contrast. These sectional shifts create "cycles of energy" that modulate intensity throughout the song, a defining characteristic of metal composition.

The composition was specifically designed to examine heaviness within the context of a fully realized, functional song rather than as an isolated sonic phenomenon. By incorporating diverse sections, from aggressive blast beats at 200 bpm to atmospheric breakdowns with modal shifts, the song provides producers with rich material to demonstrate their aesthetic approaches while maintaining the authenticity of contemporary metal music.

Learn more about the song's structure, lyrics, and compositional details →

Design Goals

The composition was designed to:

• Represent contemporary metal music aesthetics across multiple subgenres
• Include diverse musical sections for varied sonic characteristics and energy levels
• Provide sufficient complexity for producers to demonstrate their aesthetic approaches
• Feature all typical instruments in modern metal production (drums, bass, guitars, vocals)
• Incorporate sectional contrasts that naturally modulate heaviness and intensity

Professional Musicians

The original recording was performed by professional session musicians experienced in heavy metal performance. This ensured:

• Technical proficiency appropriate to the genre
• Authentic metal performance aesthetics
• Consistent source material across all producer mixes

Recording Setup & Conditions

All source tracks were recorded using professional studio equipment and techniques:

• Format: High-resolution digital audio (44.1 kHz, 24-bit)
• Tracking: Individual instrument isolation for maximum mix flexibility
• Processing: Minimal processing on source tracks to preserve mixing options
• Delivery: Multi-track stems provided to all producers in identical format

Aesthetic Goals

The original recording aimed to create a neutral foundation that could support diverse production approaches, from vintage analog aesthetics to modern hyperreal techniques. No predetermined "correct" mix existed; each producer's interpretation was equally valid for research purposes.

Career Span & Historical Representation

Producers were selected to represent the evolution of metal production from the 1970s to the 2020s:

• Classic era (1970s-1980s): Producers who shaped early heavy metal sound
• Modern era (1990s-2000s): Emergence of digital production and extreme metal aesthetics
• Contemporary era (2010s-2020s): Hyperreal production and genre diversification

This historical span allows examination of how production techniques and aesthetic preferences have evolved alongside technological developments.

Diversity of Production Aesthetics

The nine selected producers represent distinct aesthetic approaches:

International Recognition

All selected producers have:

• Multiple platinum or gold records
• Work with internationally touring metal acts
• Recognition within the metal production community
• Distinctive, identifiable sonic signatures

Independent Production

Each producer worked independently without knowledge of other producers' approaches. This ensured:

• Authentic representation of each producer's aesthetic preferences
• No influence or convergence between mixing approaches
• Maximum diversity in final production outcomes

Identical Source Material

All producers received identical multi-track stems:

• Same raw recordings for all instruments
• Same format and sample rate (44.1 kHz, 24-bit)
• Same file organization and labeling
• No pre-processing or guidance on intended sound

This controlled approach isolates the producer's creative decisions as the primary variable, allowing systematic comparison of production techniques and their perceptual effects.

Creative Freedom

Producers were given complete creative freedom:

• No aesthetic constraints: Producers could pursue any sonic goal
• No technical limitations: Any tools, plugins, or hardware could be used
• No loudness requirements: Final mastering levels at producer's discretion
• No arrangement changes: Structure remained consistent, but processing was unlimited

Deliverables

Each producer delivered:

• Stereo master mix: Final mix at producer's preferred loudness
• Individual stems: Bass, drums, guitars, vocals (and additional elements if used)
• Optional: Production notes or commentary on aesthetic choices

Participants

N = 79 participants completed the listening experiment:

• Demographics: Age range 18-65 years (M = 28.3, SD = 9.7)
• Musical background: Mix of musicians (42%) and non-musicians (58%)
• Metal expertise: Range from casual listeners to genre specialists
• Geographic distribution: Participants from UK, Germany, and other European countries

Stimuli

Participants rated ten-second excerpts from two musical sections:

Total stimuli: 18 clips (9 producers × 2 sections)

All stimuli were loudness-matched to -10.4 LUFS to control for loudness bias, ensuring that perceived differences reflected timbral and textural characteristics rather than amplitude.

Rating Scales & Operational Definitions

Participants rated each stimulus on three dimensions using 7-point Likert scales (1 = very low, 7 = very high):

Bilingual Survey Implementation

The survey was administered in two languages to maximize participant diversity:

• English version: "Heaviness", "Hardness", "Punch"
• German version: "Härte" (heaviness/hardness), "Schärfe" (sharpness), "Punch"

Translation equivalence was verified through back-translation and pilot testing. Statistical analysis confirmed no significant language effects on rating patterns.

Inter-Rater Agreement

Reliability of perceptual ratings was assessed using:

• Intraclass correlation coefficient (ICC): ICC(2,k) = 0.82-0.91 across dimensions
• Cronbach's alpha: α = 0.87-0.93 for internal consistency
• Kendall's W: W = 0.68-0.79 for rank-order agreement

These values indicate strong inter-rater agreement, confirming that participants shared consistent perceptual judgments despite individual differences in musical background and expertise.

Feature Extraction Tools

Acoustic features were extracted using established open-source libraries:

Hardness Model Implementation

Acoustic hardness was modeled using the method developed by Czedik-Eysenberg et al. (2017, 2024):

• Spectral features: Spectral centroid, spectral spread, spectral flux
• Timbral features: Roughness, sharpness, high-frequency content
• Temporal features: Attack time, zero-crossing rate
• Model output: Continuous hardness values (0-100 scale)

References:
Czedik-Eysenberg, I., Knauf, D., & Reuter, C. (2017). An acoustic hardness measure for music production research
Czedik-Eysenberg, I., Reuter, C., & Knauf, D. (2024). Revised hardness model for contemporary music

Punch Model (PM95) Implementation

Perceptual punch was quantified using the PM95 model by Fenton & Lee (2019):

• Transient detection: Onset strength function with dynamic threshold
• Attack phase analysis: Rise time and slope of amplitude envelope
• Spectral attack: High-frequency energy during onset phase
• Temporal masking: Contrast between transient and sustain phases
• Model output: Punch intensity values (arbitrary units)

Reference:
Fenton, S., & Lee, H. (2019). A perceptual model of 'punch' in musical signals

Statistical Analysis Approach

Relationships between acoustic features and perceptual ratings were analyzed using:

• Correlation analysis: Pearson's r and Spearman's ρ for linear and monotonic relationships
• Linear regression: Prediction of heaviness ratings from acoustic hardness and punch
• Multiple regression: Combined models with interaction terms
• ANOVA: Between-producer and between-section differences
• Effect sizes: Cohen's d and R² for practical significance

Key findings: Acoustic hardness strongly predicts perceived heaviness (r ≈ .78, R² ≈ .60), while punch shows weaker correlations. This suggests that spectral/textural cues are more important than temporal/transient cues for heaviness perception in metal music.

Ecological Validity

While laboratory listening conditions provided experimental control, several factors enhance ecological validity:

• Professional producers working in their own studios with familiar tools
• Participants with genuine interest in heavy metal music
• Musical excerpts representative of contemporary metal production
• Producers encouraged to use their authentic aesthetic preferences

Limitations & Future Directions

• Single composition: Results specific to this musical material; replication needed across styles
• Loudness matching: Necessary for experimental control but may reduce ecological validity
• Expert vs. novice listeners: Future work should examine expertise effects systematically
• Cultural factors: Cross-cultural studies needed to assess universality of findings

Transparency & Reproducibility

To support reproducible research:

• All audio stimuli are publicly available (see Downloads page)
• Raw perceptual data and acoustic features are provided as CSV files
• Analysis code available upon request to research team
• Detailed methodological documentation in peer-reviewed publications