Prologue: The Art and Science of Listening

Critical listening—the act of analytical auditory perception—is not merely a passive reception of sound. It is an active, continuously refined skill. This article aims to deeply explore the world of audio evaluation, unraveling the tension and synergy between objective measurements and subjective perception that lies at its core 1. While frequency response and distortion measurements provide essential foundations for evaluating audio equipment performance, we must not forget that the ultimate goal of high-fidelity systems is to create personally satisfying and emotionally engaging musical experiences for the listener 4.

This article is structured in four parts. Part One establishes a common language for describing sound quality, systematically explaining specialized terminology used in audio criticism worldwide. Part Two explores the cultural philosophy behind evaluation, examining how Japanese and Western audio criticism cultures have formed different value systems. Part Three delves into the profound scientific background of why perceptual differences arise even when conventional measurements show no change. Part Four presents a practical evaluation framework for translating all this theoretical knowledge into practice. We hope this comprehensive guide will help readers establish their own listening philosophy.

Part One: The Language of Listening — A Global Glossary

To accurately discuss audio sound quality, a common understanding of the vocabulary used in its expression is essential. This section systematically explains specialized terminology used in audio criticism worldwide, from basic elements that constitute sound to advanced concepts expressing spatial, tonal, and temporal aspects. For each term, we relate its technical definition to how it is perceived as an auditory impression.

1.1 Fundamental Concepts — The Building Blocks of Sound

Audio quality evaluation begins with basic parameters that describe physical acoustic phenomena. These concepts form the foundation for understanding more complex and subjective expressions.

Frequency Range

The human audible frequency range is generally considered to span from 20Hz to 20kHz 6. In audio equipment performance evaluation, how widely and flatly this range can be reproduced serves as one indicator. When this reproduction capability is broad, it is evaluated as “wide range” 7. This range is often further classified into more detailed regions based on auditory impressions.

• Sub-Bass: 20Hz – 60Hz. A range felt with the body rather than heard.
• Bass: 60Hz – 250Hz. Provides the foundation and depth of music.
• Midrange: 250Hz – 5kHz. The most important band containing human voices and fundamental frequencies of many instruments.
• Treble: 5kHz – 20kHz. Governs clarity and brilliance of sound 6.

Human hearing tends to lose sensitivity to high frequencies with age 9. Sensitivity also varies by frequency depending on volume. This is known as the “equal loudness curve (Fletcher-Munson curve),” showing that human ears become less sensitive to low and high frequencies at low volumes 10. This psychoacoustic characteristic is one reason why loudness compensation is needed when listening at low volumes.

Dynamic Range

Dynamic range indicates the difference between the quietest and loudest sounds an audio system can reproduce 7. Systems with wide dynamic range possess the ability to express everything from subtle sounds emerging from silence to the powerful tutti of an orchestra without breakdown. Dynamic range is evaluated from two aspects.

• Macrodynamics: The ability to express large volume changes from pianissimo to fortissimo. Excellence here creates scale and impact in music 13.
• Microdynamics: The ability to reproduce minute volume changes within a single sound or performance nuances. Excellence here conveys delicate expression in performance, making music feel more vivid 13.

Signal-to-Noise Ratio (S/N Ratio)

S/N ratio expresses in decibels (dB) the ratio between the intended musical signal and unwanted background noise generated by the equipment itself 7. Higher values indicate less noise. Auditorily, high S/N ratio is perceived as “silence” during quiet passages. When the background feels completely “black,” subtle musical information previously buried in noise (low-level detail 14) becomes clearly audible, and sounds during performance feel clean without extraneous noise 7.

Distortion

Distortion refers to unwanted components that were not present in the original signal being added during the reproduction process. The most commonly measured is Total Harmonic Distortion + Noise (THD+N), which combines harmonic distortion appearing at integer multiples of the signal frequency with other noise components 15.

While low measured distortion is a prerequisite for high fidelity, how that distortion is perceived is highly complex. For example, even-order harmonic distortion (2nd, 4th, etc.) harmonizes easily with the original sound, making it relatively non-offensive and sometimes favorably received as a “euphonic” effect that adds “richness” or “body” to the sound 6. The “warm” sound of tube amplifiers is often attributed to this dominance of even-order distortion. Conversely, odd-order harmonic distortion (3rd, 5th, etc.) tends to form dissonance and is more likely to be perceived as cold, hard, and harsh.

Specific distortion expressions used in subjective evaluation include:

• Sibilance: The phenomenon where female vocals’ “s” sounds or cymbal sounds feel sharp and piercing to the ear. This stems from specific distortion or peaks in the high-frequency band 19.
• Grain: A state where sound, particularly in the mid-high range, feels rough or granular. Analogous to grain in photography 6.

1.2 Spatial Dimension — Scenic Description Through Sound

The essence of stereo reproduction lies in recreating three-dimensional acoustic space between speakers. Specialized vocabulary is used to evaluate the quality of this space.

Soundstage

Soundstage refers to the breadth of the virtual performance space that appears in the listening room through stereo reproduction 21. Excellent systems make speakers disappear, creating the illusion of live performance unfolding before you. Soundstage is primarily evaluated by three elements:

• Width: Whether the soundstage extends beyond the left and right speakers.
• Depth: Whether the distance from front-row to back-row instruments is expressed.
• Height: Whether vertical spread is felt in the soundstage.

In criticism, soundstages that are “crammed” or “vague” between speakers are negatively evaluated 24. In contrast, “enormous,” “majestic,” or “deep” soundstages are highly praised as evidence that the system possesses high spatial reproduction capability 24.

Imaging and Focus

Imaging refers to the ability to clearly delineate where individual instruments and vocals are positioned within the soundstage 20. Focus indicates how sharp the outline of those sound images is. In systems with excellent imaging, vocals are clearly positioned center, guitar to the right, piano to the left, with each sound source “specifically located” and “sharply focused” 13. Conversely, poor imaging causes sound images to appear “blurred” or waver in position. The ultimate goal is for speakers to “virtually disappear,” leaving only the music itself manifested in space 24.

Separation and Air

Separation indicates whether the “space” between instruments can be heard—whether individual sounds are heard separately without congestion 22. Poor separation makes the entire sound seem like a “congested” or “muddy” mass.

“Air” refers to the ability to reproduce subtle reverb and atmosphere surrounding instruments 27. This arises from extremely excellent high-frequency extension and faithful reproduction of minute reflected sounds from the recording venue. Rich air makes the soundstage feel more open and realistic 8.

For those interested in deep dive into spatial audio imaging (ΦωΦ)

1.3 Tonal Dimension — Sound’s Personality and Character

Terms expressing sound’s “coloration” or “texture” represent one of the most metaphorical and subjective areas in audio evaluation. The Japanese word “音色” (onshoku/neiro) encompasses two different concepts, requiring context-dependent usage.

Timbre vs. Tonality

• Timbre: Physically refers to the instrument-specific sound character determined by waveform, particularly overtone composition 29. When the same pitch (e.g., middle “A”) is played, piano and violin sound different due to different timbres. High-fidelity systems are required to accurately reproduce this timbre and distinguish between the sound differences of a Stradivarius and Guarneri.
• Tonality: Refers to the overall “tone” or “character” of reproduced sound that audio equipment or entire systems possess 15. This is equipment-specific “coloration,” a different evaluation axis from faithful timbre reproduction. Tonality is expressed through descriptive terms like those below.

The Tonality Spectrum

• Warm: A tone rich in mid-low frequencies with full midrange. Comfortable to listen to, often described as “pleasant” or “lush” 8.
• Bright: A tone emphasizing mid-high to high frequencies. While details stand out, excessive brightness can become “harsh” or “edgy” and irritating 6.
• Neutral/Uncolored: A balanced tone without bias toward specific frequency bands. Theoretically considered the ideal form of “accurate” reproduction 15.
• Dark: A tone with suppressed highs and emphasized lows. The polar opposite of “bright” 8.

1.4 Temporal Dimension — The Pulse of Music

Music is a temporal art, and the ability to correctly convey its rhythm and dynamics is extremely important in measuring audio system performance.

Transient Response

Transient response indicates how nimbly a system can follow steep changes in musical signals, particularly the onset (Attack) and decay (Decay/Release) of sounds 6.

Excellent transient characteristics are described as “fast” or “crisp,” with piano attacks and drum rim shots reproduced sharply and cleanly. Poor transients feel “slow,” causing sounds to “smear” or unwanted resonances to “hang over,” blurring musical contours 34.

Pace, Rhythm, and Timing (PRaT)

PRaT is a concept particularly valued in British audio journalism, evaluating how well a system can convey music’s driving force and rhythmic cohesion 6. When listening to music on systems with excellent PRaT, you naturally want to tap your foot to the rhythm and feel drawn into the music. In criticism, this is praised with words like “rhythmic drive” or “good timing” 40. In systems with poor PRaT, even if tonally accurate, music can sound flat and lifeless.

Table 1: Key Subjective Evaluation Terms (Comparative Glossary)

The following table summarizes the major audio evaluation terms explained in this chapter, comparing Japanese and English expressions with cultural context.

1.5 Detailed Glossary — Vocabulary for Describing Sound Texture and Flaws

Beyond basic terms, specialized expressions exist for describing more delicate sound nuances and specific flaws. Understanding this vocabulary is extremely useful for deeply interpreting critical articles and articulating one’s own listening impressions.

Texture and Detail

• Texture/Texturing: Refers to perception of surface texture or structure in sound 15. Like grain in photography, expresses whether sound feels smooth or rough. This includes the texture of string instruments’ bow friction or the breath in vocals 22.
• Resolution/Definition: The ability to delineate minute information contained in music 100. High-resolution systems clearly reproduce low-level details like reverb tails and individual orchestra instruments 14.
• Transparency: A state where sound has no muddiness or cloudiness, providing clear visibility 15. Like wiping a dirty window clean, refers to the sensation where musical details can be clearly perceived. High S/N ratio and low distortion contribute to high transparency 32.
• Palpable/Tangible: The sensation where sound images exist in space with such reality that they seem touchable rather than mere collections of sound 102. Refers to vocals and instruments appearing with vivid presence.
• Holographic: A state where soundstage and imaging are both achieved at extremely high levels, with sound images perceived as three-dimensional entities with width, height, and depth 103. Creates the illusion that speakers completely disappear and the performance space itself is recreated in the listening room 103.

Tonal Character and Richness

• Liquid/Fluid: Sound that is not harsh but smooth, cohesive, and flows naturally 32. Often used for midrange expression.
• Silky: High frequencies that are velvet-smooth, delicate, and open 37. Praise for pleasant, extended treble without harsh peaks.
• Sweet: Smooth, gentle, and delicate high-frequency expression 37. Refers to pleasant highs without excessive stimulation that don’t cause listening fatigue.
• Rich/Lush: Abundant, full, sensual resonance 14. Particularly rich mid-low harmonics that give thickness and warmth to the entire music.
• Bloom: The sensation of sound opening like a flower, spreading richly 107. Refers to the warm resonance of instruments like cello or acoustic guitar filling space.
• Weight/Heft: Feeling of heaviness, stability, and physical power in sound, particularly in the bass 12. Creates the impression that music is built on a solid foundation without lightweight sound.
• Lean: A state where bass is somewhat lacking and sound feels thin overall 14. Used when bass is even more restrained than “cool” tonality.
• Dry: Sound with little reverb component and poor resonance 101. Similar to sound in dead recording environments or overly absorptive listening rooms.
• Sterile/Clinical: Extremely clean sound without distortion but lacking musical appeal or emotional resonance 37. Often used with the nuance that while suitable for analytical listening, it lacks immersion.

Negative Artifacts and Colorations

• Glare: Excessively bright, unpleasantly piercing sound 108. Occurs when energy is overly concentrated in the mid-high frequencies.
• Etch/Edgy: A state where sound contours are overly emphasized, feeling hard and sharp 101. Details are clearly audible but unnatural and fatiguing.
• Shrill/Strident: Metallic, harsh, piercing sound 37. Extremely unpleasant sound quality caused by high-frequency peaks or distortion.
• Gritty/Grainy: A state where sound feels rough or granular 15. The opposite of smoothness.
• Hash: Very rough, noise-like texture with sharp edges 109. Refers to particularly harsh types of distortion.
• Smear/Blurred: Poor transient characteristics causing unclear sound contours 6. Individual sounds become temporally smeared, losing detail.
• Congestion/Muddy: A state where sounds don’t separate and seem mixed together 14. Particularly common when mid-low resolution is poor, reducing overall clarity.
• Veiled: Loss of sound clarity, as if listening through a thin veil that obscures details 32. Often caused by high-frequency rolloff or noise.
• Boomy: Excessive, uncontrolled resonance in mid-bass (especially around 125Hz) 107. Specific bass frequencies are emphasized, prone to “one-note bass.”
• Boxy: Coloration where the speaker enclosure itself resonates, making sound seem trapped inside a box 107. Unwanted resonance added particularly in mid-bass (around 250-500Hz).
• Honky/Nasal: Unnatural resonance like speaking through cupped hands or with a pinched nose 15. Occurs with strong peaks at specific midrange frequencies (around 500-700Hz).

Dynamics and Impact

• Slam/Punch: Words expressing bass impact and striking force. Refers to powerful reproduction where drum kicks and bass attacks are felt as physical impact 37.
• Coherence: In multi-way speakers, the seamless, smooth connection of sound from each driver unit (woofer, tweeter, etc.) so they sound like a single source 107.
• Speed: Perceptual impression of how quickly a system follows steep musical changes 37. Refers to transient speed and the ability to reproduce overall musical pace without lag.

Part Two: Evaluation Culture — Philosophical Conflicts and Common Ground

The act of evaluating audio equipment sound quality extends beyond mere technical analysis. It reflects deep philosophy and cultural values regarding what evaluators consider “good sound.” This chapter explores audio evaluation culture from three different perspectives: the two giants who shaped Japanese audio criticism, the subjective criticism movement in the West, and the rise of modern objectivism.

2.1 Japanese Aesthetics — Craftsmanship, Presence, and Energy

Japanese audio criticism culture is rooted in unique aesthetics and philosophy. Representative figures include Sugano Okihiko and Nagaoka Tetsuo—contrasting yet enormously influential critics.

Sugano Okihiko: Philosophy of “Mechanical Beauty”

Sugano Okihiko viewed audio equipment not merely as sound reproduction devices but as “machines” possessing craftwork beauty. The core of his philosophy is captured in these words: “I believe mechanical beauty is the essence born when pursuing performance” 47. He believed that design born from functional necessity—form stripped of vanity—contains true beauty, and equipment with such beauty inevitably produces excellent sound. This philosophy connects to Japan’s “takumi” (artisan) spirit, showing unique values where detailed craftsmanship and tactile elements are inseparable from sound quality. His criticism went beyond mere sound quality reporting, possessing literary character that depicted the lifestyle of placing audio equipment in living spaces and confronting music 48.

Nagaoka Tetsuo: Pursuit of “Sound Separation” and Dynamic Power

In contrast to Sugano’s aesthetic approach, Nagaoka Tetsuo maintained an extremely practical, performance-supremacist philosophy. His most valued evaluation criterion was “sound separation” (音離れ)—transient speed 44. He considered quick sound onset and clean decay the primary condition for good sound, accepting some tonal quirks (coloration) to achieve this. The back-loaded horn speakers he designed and recommended embodied this philosophy, known for overwhelming dynamics and speed while having characteristic resonance 44. His famous sayings like “Audio is volume” and “Amplifiers are weight” succinctly express his emphasis on power to fully reproduce music’s energy and the robust physical foundation (heavy chassis and power supplies) to support it 44. He always considered cost-performance and had a practical instructor side, publishing designs many audiophiles could attempt as DIY projects.

2.2 Anglo-American Tradition — Subjectivism, Musicality, and Rhythm

Western audio criticism, particularly in America and Britain, is deeply rooted in a subjectivist tradition that places “listening” itself at the center of evaluation.

J. Gordon Holt and the Birth of Subjective Criticism

J. Gordon Holt is considered the father of modern subjective audio criticism. He founded Stereophile magazine in 1962, challenging the prevailing practice of evaluating equipment solely through measurements 51. His philosophy was simple and clear: “The best way to evaluate audio products is to do exactly what the purchaser would do—listen to them.” He systematized subjective vocabulary like “warm” and “harsh,” now commonly used, establishing the language of audio criticism 51. The “Recommended Components” format, listing outstanding components, was also his creation, with immeasurable influence 53.

Robert Harley and The Absolute Sound: Supremacy of Listening Experience

J. Gordon Holt’s legacy continues through The Absolute Sound magazine, founded by Harry Pearson, and its current editor Robert Harley. Harley’s philosophy centers on whether audio equipment sounds like “the real thing” and can convey musical emotion 4. He clearly supports the idea that measurements don’t necessarily correlate with our listening experience, resonating with this article’s central theme 4. His writings provide practical insights for maximizing system performance through listening.

British PRaT

British audio criticism, especially represented by What Hi-Fi? magazine, distinctly emphasizes “Pace, Rhythm, and Timing (PRaT)” 39. This evaluates how skillfully a system can express music’s tempo, rhythmic accuracy, and timing cohesion. Under this philosophy, even tonally perfect neutral systems aren’t highly rated if they can’t convey music’s drive and momentum. Criticism praises “rhythmic drive” and “precise timing” 40 while harshly criticizing systems that “lack dynamic expression” 45. This reflects cultural values prioritizing musical immersion and “fun factor” over analytical fidelity.

2.3 Modern Objectivist Movement — Pursuit of Verifiable Truth

As a powerful counter to traditional subjectivist criticism, an objectivist movement treating measurements as absolute standards has gained significant influence.

Amir Majidimehr and Audio Science Review (ASR): Measurement-First Paradigm

Audio Science Review (ASR), a website founded by former Microsoft engineer Amir Majidimehr, is this movement’s epicenter 56. ASR’s philosophy involves thoroughly measuring objective data like SINAD (signal-to-noise and distortion ratio) using high-performance Audio Precision instruments, then evaluating equipment performance based on these results. This approach identifies engineeringly excellent, auditorily transparent equipment while scientifically criticizing poor-performing products.

Objectivist Claims and Criticism of Subjectivists

From ASR’s perspective, most perceived sound quality differences between electronic equipment (DACs, amplifiers) with sufficiently excellent measurements result from cognitive biases like placebo effects and confirmation bias rather than actual acoustic differences 56. Therefore, they argue the only scientific method for verifying subjective claims is rigorously controlled blind testing (ABX testing) 58.

Subjectivist Counterarguments

However, criticism of ASR’s approach exists. Critics argue that excessive focus on limited measurement categories like SINAD may overlook other important performance aspects like transient response and spatial reproduction capability that standard measurements can’t fully capture 56. They also point out that the stance “what can’t be measured doesn’t exist” underestimates psychoacoustics’ complexity, which isn’t fully understood 56.

Comparing these different philosophies leads to one important conclusion: “good sound” definition isn’t universal but is formed by cultural priorities. Japanese critics’ emphasis on craftsmanship aesthetics (Sugano) and raw energy (Nagaoka), British critics’ pursuit of rhythmic enjoyment (PRaT), American subjectivists’ quest for realistic acoustic space reproduction (Holt/Harley), and objectivists’ faith in measurement perfection (ASR)—all represent legitimate value systems illuminating diverse aspects of the audio hobby. When reading criticism, understanding the writer’s cultural and philosophical background is key to correctly interpreting their evaluation.

Part Three: Beyond the Graphs — Exploring Factors Behind Audible Differences

One of audio’s hottest debates concerns why audible differences arise between equipment with seemingly identical measurements. Despite no significant differences in basic measurements like frequency response or THD+N, many listeners report clear sound quality differences. While often dismissed as psychological bias (placebo effect), this chapter deeply explores the scientific and technical factors behind this phenomenon. From digital domain timing precision to analog circuit power supply quality to final sound-radiating physical structures, we explore sources of differences that don’t easily appear in conventional graphs.

3.1 Digital Domain — The Subtleties of Timing and Filtering

Digital audio quality isn’t determined solely by accurate “0” and “1” data (bit-perfect). When that data is processed—timing precision—and the philosophy of converting data to analog signals decisively impact sound quality.

Jitter: Enemy of Timing Precision

Jitter refers to minute timing fluctuations in digital signals 60. When digital data reaches the D/A converter at incorrect timing, distortion occurs during analog waveform conversion. Modern high-performance DACs excel at suppressing this jitter through internal clocks (jitter rejection), but complete elimination is difficult. Residual jitter can blur sound contours (“smear”) and particularly damage stereo image stability and sound image focus 61. AES (Audio Engineering Society) papers recognize jitter’s potential audible impact, suggesting that even very low levels can affect sound transparency and subtle nuance reproduction 63. This provides scientific basis for how two bit-perfect data streams can ultimately differ in sound quality due to transmission path (transport) timing precision differences.

DAC Design Philosophy Conflict: Non-Oversampling (NOS) vs. Oversampling (OS)

DAC design philosophy differences represent the most symbolic example explaining measurement and auditory perception divergence.

• Oversampling (OS) Mechanism: Current mainstream OS DACs use internal digital filters to multiply input digital signals to much higher sampling frequencies (oversampling) 65. This distances unwanted high-frequency noise (aliasing) generated during D/A conversion from the audible band. Consequently, subsequent analog filters can be designed with gentle characteristics, reducing phase distortion within the audible band. This method produces excellent measurement results like flat frequency response and low distortion 65.

• Non-Oversampling (NOS) Mechanism: NOS DACs, enjoying strong support from some audio enthusiasts, intentionally omit this digital filter, performing D/A conversion at the original sampling frequency 66. Supporters dislike artifacts caused by digital filters, particularly unnatural resonance appearing before impulse signals (pre-ringing). Pre-ringing doesn’t exist in nature, and they argue it damages sound onset sharpness and liveliness. NOS DACs don’t inherently generate pre-ringing, supposedly yielding more “natural,” “smooth,” and “analog-like” sound 65.

• Trade-offs Exist: The NOS method’s “cost” is measurement degradation. Without digital filters, steep analog filters are needed to remove aliasing noise, but problems like high-frequency attenuation (rolloff) and high-frequency components folding back into audible distortion (imaging artifacts) remain unavoidable 66. Here we see a typical example where measurements and auditory evaluation can reverse. OS DACs are measurably “accurate” but may sound “unnatural” to some listeners, while NOS DACs are measurably “inaccurate” but may sound “musical” to some listeners. This isn’t a simple matter of which is superior, but a design philosophy difference regarding what type of “imperfection” to tolerate.

3.2 Analog Domain — Importance of Clean Foundation

However perfect digital signals may be, what ultimately reaches our ears is analog signals. Analog circuit performance greatly depends on the power supply quality forming its foundation and characteristics of physical components through which signals pass.

Power Supply Quality and Noise

All audio circuits operate on direct current (DC) power. When this power contains noise (ripple or fluctuation), it modulates audio signals, severely degrading sound quality 70. This power supply noise, which doesn’t easily appear in frequency response or THD measurements under ideal test conditions, is auditorily perceived as background “muddiness” or “veiling,” causing dynamic range reduction and fine detail masking 72. Audio enthusiasts invest in high-quality power supplies and power conditioners to secure this “clean foundation” and protect signal integrity.

Speaker Enclosure Material and Resonance

Speakers are affected not only by driver units but also by enclosures housing them 73. Ideal enclosures are acoustically completely inert, not producing sound themselves. However, all materials have inherent resonant frequencies.

• MDF (Medium Density Fiberboard): With high density and uniform internal structure, it effectively suppresses (damps) resonance, making it widely adopted for speaker enclosures 74.
• Plywood: Widely used like MDF but may have characteristic resonance due to layered structure 74.
• Solid Wood: With non-uniform density and characteristics changing with temperature and humidity, resonance control is difficult, generally considered unsuitable for speaker enclosures 75.
• Plastic/Resin: Without sufficient thickness and internal reinforcement, it easily resonates, often causing “boxy” sound 76.

Even using identical drivers and crossover networks, different enclosure materials or internal reinforcement structures manage resonance differently, clearly changing final sound. This difference can’t be completely captured by simple on-axis frequency response measurements alone.

Cable Controversy: Scientific Perspective

One of audio’s most heated debates involves cables. From an objectivist standpoint, cables with appropriate conductor cross-section (gauge) and no defects shouldn’t produce audible sound quality differences 77. However, subjectivists and manufacturers claim that conductor material and purity, insulation (dielectric) material’s energy-absorbing “dielectric absorption” phenomenon, and external noise shielding performance affect sound quality 78.

Scientifically approaching this controversy, cables’ electrical characteristics—capacitance, inductance, resistance—can interact with connected equipment’s input/output impedance, potentially functioning as filters especially at high frequencies. While usually very subtle, this influence could theoretically appear as audible changes depending on system combinations. More importantly, cable replacement itself creates strong expectation bias in listeners, which, combined with memory-based comparison uncertainty, receives significant psychological influence 77.

3.3 Final Frontier — Psychoacoustics and Perception

Psychoacoustics provides the perspective integrating all previous discussions. Human brains function not as precision measuring instruments like audio analyzers, but as highly sophisticated pattern recognition systems 79.

Psychoacoustic Weighting of Errors

More important than measured error “quantity” is likely their “type.” Human hearing, from survival instincts, is extremely sensitive to sound onsets and temporal changes (transients) 79. Therefore, “temporal errors” like digital filter pre-ringing or jitter-induced image wavering are easily recognized as “unnatural” artifacts by the brain. Conversely, “tonal errors” like gentle high-frequency rolloff in NOS DACs or low-order harmonic distortion generated by tube amplifiers, being similar to natural acoustic phenomena, may be more tolerantly accepted by the brain or favorably interpreted as “musical” resonance 81.

Masking Effects

Another important psychoacoustic concept is masking—the phenomenon where one sound becomes inaudible due to another louder sound 79. In complex musical passages, considerable distortion components are masked by original musical signals, becoming less perceptible. However, when music becomes quiet, minute power supply-derived noise floors become perceptible, affecting impressions of “silence quality” or “black background.”

In conclusion, audible differences not appearing in measurements result from complex interactions of timing precision, analog circuit quality, physical resonance, and psychoacoustic factors determining how human brains interpret these errors. True audio evaluation pursuit involves not only achieving perfect measurements but also determining which types of “imperfection” are least harmful or most pleasantly resonant to musical experience.

Part Four: Critical Listening Practice Guide

Based on theoretical knowledge thus far, this chapter provides practical frameworks for readers to conduct systematic and effective sound quality evaluation. We explain specific procedures from environmental setup to maximize system performance, to selecting reference sources as evaluation standards, to comparative listening methods for objectively verifying subjective impressions.

4.1 Environmental Preparation — The Room as the Final Component

Audio system sound quality is greatly influenced by room acoustic characteristics. Recognizing the room itself as the final and most influential component is the starting point for critical listening.

Speaker and Listener Placement

Optimal soundstage and frequency balance require extremely important speaker and listening position placement.

• Equilateral Triangle Placement: Basic placement forms an equilateral triangle between left and right speakers and listening position. This provides the most stable stereo image 84.
• Distance from Walls: Placing speakers too close to walls, especially rear and side walls, can unnaturally emphasize bass or cause primary reflections to interfere with direct sound, blurring sound images (SBIR: Speaker-Boundary Interference Response). Generally, at least 1m distance from walls is recommended, though adjustment according to room conditions is necessary 84.
• Listening Position: The exact center of room length or wall proximity can extremely strengthen or weaken specific frequencies due to standing wave influence. It’s desirable to find locations where bass response is flattest, referencing positions like 38% of room length (the “38% rule”) 84.

Basic Acoustic Adjustment

Even without professional measuring instruments, basic room acoustic treatment dramatically improves sound quality.

• Primary Reflection Point Treatment: “Primary reflection points” exist on side walls and ceiling between speakers and listening position where initial sound reflections occur. Installing absorption panels at these points significantly reduces sound image blur and frequency response disturbance. Primary reflection points can be easily found using the “mirror trick”—sitting at the listening position with a mirror against the side wall where speakers appear in the reflection 84.
• Bass Treatment: Low-frequency energy tends to accumulate in room corners. Installing “bass traps”—low-frequency absorption materials—in room corners can improve boomy, unclear bass and achieve tighter reproduction 84.

4.2 Reference Playlist Construction — Evaluation Tools

Reliable reference sources serving as “measuring sticks” are essential for consistent evaluation.

Selection Criteria

Reference playlists should be constructed based on these criteria:

• Familiar Sources: Most importantly, knowing the music intimately down to details. Repeated listening forms internal standards for “how that recording should sound” 88.
• Diversity: Include wide-ranging genres—classical, jazz, rock, electronic music—rather than specific genre bias. This evaluates diverse system aspects (dynamics, timbre, rhythm, etc.) 89.
• Recording Quality: Include not only high-quality “audiophile recordings” but also intentionally compressed sources and older recordings with narrow dynamic range. This evaluates not only system resolution but also “tolerance” for making music enjoyable 89.

Recommended Reference Tracks

The following table provides particularly useful music examples for evaluating each system performance aspect, with guidance on which acoustic aspects to focus on.

Table 2: Recommended Reference Tracks for System Evaluation

4.3 Comparison Techniques — A/B Testing and ABX Testing

Using systematic methods is effective for more rigorous equipment comparison evaluation.

Level-Matched A/B Testing

When comparing two pieces of equipment (A and B), the most important aspect is strictly matching their reproduction volume levels. Human hearing tends to misperceive louder volume as “better sound quality” even with just 0.5dB differences 93. For comparison, repeatedly playing short phrases from the same music while quickly switching is effective.

ABX Blind Testing Introduction

ABX testing is a method for scientifically verifying whether perceived sound quality differences are real or result from psychological bias 94.

• Procedure: Listeners can freely compare known sources A and B. Then unknown source X is presented. X is identical to either A or B, and listeners guess whether X matches A or B. This trial is repeated multiple times (e.g., 10+ times), determining whether accuracy rates statistically significantly exceed chance (50%) to judge if audible differences between A and B are identifiable 97.
• Practice: PC music playback software like Foobar2000 provides plugins for conducting ABX tests 98. Using this, you can verify differences between uncompressed WAV files (A) and high-bitrate MP3 files (B). This method becomes a powerful tool for self-verifying expensive cable and accessory effects.

Conclusion: Cultivating Your Own Listening Philosophy

This article has comprehensively explored audio evaluation’s diverse aspects: precise language for describing sound, cultural values underlying evaluation, profound science creating sound quality differences unmeasurable by numbers alone, and practical methods for self-verification. This knowledge should serve as a compass for enjoying audio as a hobby more deeply and intellectually.

The important thing is not adhering to single doctrine. Pure subjectivism and strict objectivism each have limitations in capturing audio’s complete picture. Science provides powerful foundations for understanding what we hear. Knowing why factors like jitter, digital filter characteristics, and power supply noise can create audible differences frees us from baseless myths. Simultaneously, methods like ABX testing help us recognize our own cognitive biases, becoming more humble listeners.

However, what ultimately determines audio system value isn’t measurement superiority but the richness of musical experience it provides. Sugano Okihiko’s mechanical aesthetics, Nagaoka Tetsuo’s pursuit of musical energy, British critics’ emphasis on rhythmic enjoyment—all show different yet equally valuable approaches to musical enjoyment.

Armed with knowledge gained from this article, readers no longer need to blindly accept others’ evaluations. You can trust your own ears while recognizing their limitations, refining your own listening sense. You can define what “high fidelity” means to you and confidently build systems realizing those personal ideals. This “Listener’s Compass” doesn’t point to one absolute destination. It’s your personal compass for navigating the vast, fascinating audio world with deep insight and conviction.

References

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