WAVGEN Music World 09 — Psychoacoustics Lab

02 · EQUAL-LOUDNESS LANDSCAPE

ISO 226 CONTOURS — THE TOPOGRAPHY OF PERCEPTION

LISTENING LEVEL 70 dB

TONE A (AMBER) 100 Hz TONE B (CYAN) 1000 Hz

EQUAL LOUDNESS — At low SPL, bass sounds weaker proportionally. The curves bow upward at the frequency extremes, meaning more physical energy is needed to achieve equal perceived loudness. Loudness controls on hi-fi systems compensate for this by boosting bass and treble at low listening levels.

03 · THE MASKING SHADOW

SIMULTANEOUS & TEMPORAL MASKING — HOW LOUD SOUNDS ERASE QUIET ONES

MASKER FREQUENCY 1000 Hz

MASKER LEVEL 70 dB TARGET FREQUENCY 2000 Hz

PERCEPTUAL MASKING — Perceptual audio codecs (MP3, AAC) exploit masking to discard sounds hidden in the masking shadow. The masking curve is asymmetric: a loud tone masks more on the high-frequency side than the low. Temporal masking persists ~200ms after the masker stops.

04 · THE CRITICAL BAND SIEVE

24 BARK-SCALE BANDS — THE AUDITORY FILTER BANK

PRESET DEMO

FREQ A 400 Hz FREQ B 500 Hz

CRITICAL BANDS — The auditory system has ~24 critical bands (Bark scale). Sounds within one band compete for neural resources, causing roughness, beating, and masking. Sounds in different bands are processed independently and perceived as distinct tones.

05 · THE HAAS EFFECT TIMELINE

PRECEDENCE EFFECT — HOW TIMING DOMINATES LEVEL IN LOCALIZATION

DELAY (SPEAKER B) 10 ms

B LEVEL OFFSET +0 dB

HAAS / PRECEDENCE EFFECT — The brain fuses the first-arriving sound with its echo if the delay is under ~35ms, localizing toward the earlier speaker. Concert PA systems delay side-fill speakers to align perception with the stage. Above 35ms, the delayed sound becomes a distinct echo.

06 · BINAURAL BEAT MACHINE

INTERAURAL FREQUENCY DIFFERENCE — USE HEADPHONES

LEFT EAR — CARRIER

RIGHT EAR — CARRIER + BEAT

BRAINWAVE ZONES (beat frequency Hz)

δ DELTA 0.5–4

θ THETA 4–8

α ALPHA 8–12

β BETA 12–30

γ GAMMA 30–40

CARRIER FREQUENCY 220 Hz

BEAT FREQUENCY 10 Hz

SCIENCE: Binaural beats create a real perceptual pitch corresponding to the frequency difference between ears — a genuine auditory illusion processed in the superior olivary complex.

PSEUDOSCIENCE: Claims that specific frequencies reliably entrain brainwaves to produce measurable cognitive effects (focus, sleep, creativity) lack strong peer-reviewed evidence. Effects observed in small studies may reflect expectation and relaxation rather than neural entrainment.

07 · LOUDNESS WAR ARCHAEOLOGY

1980–2024 — THE COMPRESSION OF MUSIC

SELECT ERA

LUFS: -20

DR: 14

DYNAMIC RANGE: FULL DYNAMIC RANGE

LOUDNESS WAR — Streaming platforms normalize all tracks to −14 LUFS, meaning loud masters play back quieter than dynamic ones. DR values dropped from ~14 in the 1980s to ~5 at the peak (Death Magnetic, 2008). Since 2016, streaming normalization has reversed the incentive to over-compress.

08 · THE COCKTAIL PARTY PROBLEM

AUDITORY STREAM SEGREGATION — SELECTIVE ATTENTION IN NOISE

REVERB AMOUNT LOW

DRAG SPOTLIGHT OVER SOURCES

COCKTAIL PARTY EFFECT — The brain performs selective attention automatically, locking onto one audio stream among many. No algorithm perfectly replicates this capability — it remains an open research problem in computational auditory scene analysis (CASA). The phenomenon relies on spatial, spectral, and temporal cues simultaneously.

09 · EAR FREQUENCY MAP

TONOTOPIC ORGANIZATION — THE COCHLEA AS A FREQUENCY RULER

FREQUENCY PROBE 1000 Hz

INSTRUMENT OVERLAY

TONOTOPIC ORGANIZATION — The cochlea physically maps frequencies along its length. Hair cells at the apex respond to bass; those at the base respond to treble. This spatial frequency mapping is preserved throughout the auditory pathway up to the primary auditory cortex (A1). Overlapping instrument harmonics compete for the same hair cells.

10 · OTOACOUSTIC EMISSION SIMULATOR

COMBINATION TONES — WHEN THE EAR GENERATES ITS OWN FREQUENCIES

F1 (AMBER) 500 Hz

F2 (CYAN) 600 Hz

2f1−f2: 400 Hz f1+f2: 1100 Hz

MARYANNE AMACHER — Amacher's "Third Ear Music" deliberately induced otoacoustic emissions at high SPL — the ear itself became part of the composition, generating difference tones not present in the loudspeakers. The cochlea's active nonlinearity produces combination tones (2f1−f2) audible to the listener but measurable with a microphone in the ear canal.

11 · ARTISTS OF PSYCHOACOUSTIC PRACTICE

COMPOSERS & SOUND ARTISTS WHO MADE THE EAR THE MEDIUM

ALVIN LUCIER

Room acoustics, standing waves, brainwave sonification

I Am Sitting in a Room (1969)

Recorded speech re-recorded until the room's resonant frequencies obliterate the original words, leaving pure acoustic signature.

MARYANNE AMACHER

Otoacoustic emissions, architectural sound, extreme SPL

City-Links (1967–1980)

Used the ear's own nonlinear distortion as a compositional instrument — the listener's cochlea generated tones not in the loudspeaker signal.

RYOJI IKEDA

Sinusoidal precision, data sonification, threshold perception

test pattern (2008–)

Works at the perceptual limits of frequency and time, making audible the boundary between signal and noise at the edge of hearing.

LA MONTE YOUNG

Just intonation, drone, sustained frequency ratios

The Well-Tuned Piano (1964–)

Extended duration exposes the beating patterns of just intervals — psychoacoustic phenomena become structural elements of the composition.

ÉLIANE RADIGUE

Analog synthesis, feedback, slow spectral evolution

Trilogie de la Mort (1988–1993)

Works emerge from the psychoacoustics of near-unison frequencies — difference tones, beating, and sum tones heard as autonomous phenomena.

FRANCISCO LÓPEZ

Environmental recordings, blindfolded listening, absolute sound

La Selva (1997)

Strips visual context to isolate pure auditory experience — the listener's perceptual system becomes the sole interpretive apparatus.

PAULINE OLIVEROS

Deep listening, somatic attention, improvisation

Deep Listening (1989)

Theorized listening as a distinct cognitive practice from hearing — conscious direction of attention changes what the auditory system extracts from sound.

WALTER MURCH

Film sound design, psychoacoustic mixing, editorial rhythm

Apocalypse Now (1979)

Developed the theory that film cuts feel natural when synchronized with eye blinks and inner speech — perception as an active, predictive process.

12 · GLOSSARY

24 TERMS — THE LANGUAGE OF PSYCHOACOUSTICS

EQUAL LOUDNESS: Contours showing the SPL required at each frequency to match the perceived loudness of a 1kHz reference tone.
PHON: Unit of loudness level. A tone of N phons sounds as loud as a 1kHz sine wave at N dB SPL.
MASKING THRESHOLD: The SPL below which a target sound is rendered inaudible by a louder masker tone or noise.
CRITICAL BAND: A frequency band within which two tones interact perceptually — causing beating, roughness, and mutual masking.
BARK SCALE: A psychoacoustic frequency scale with 24 bands corresponding to the critical bands of the human auditory system.
HRTF: Head-Related Transfer Function — the frequency-dependent filtering applied by the head, ears, and torso to localize sound in 3D space.
HAAS EFFECT: The perceptual fusion of a direct sound and its early reflection (under ~35ms delay) into a single perceived event localized toward the first arrival.
PRECEDENCE EFFECT: The dominance of the first-arriving sound in determining perceived location when two identical sounds arrive within a short time window.
BINAURAL BEAT: A perceived low-frequency oscillation when slightly different frequencies are presented separately to each ear — processed in the brainstem.
OTOACOUSTIC EMISSION: Sound generated by the cochlea's active outer hair cells, measurable in the ear canal — evidence that the ear is not purely passive.
AUDITORY STREAM SEGREGATION: The perceptual grouping of acoustic elements into separate "streams" — the basis of following one voice in a noisy room.
TONOTOPIC ORGANIZATION: The spatial mapping of frequency along the cochlea and auditory cortex — bass at the apex, treble at the base.
PSYCHOACOUSTICS: The scientific study of the perception of sound — how the auditory system interprets, distorts, and enriches physical acoustic signals.
PERCEPTUAL CODING: Audio compression that exploits masking, critical bands, and threshold of hearing to discard inaudible data.
LUFS: Loudness Units relative to Full Scale — the broadcast and streaming standard for integrated loudness measurement (ITU-R BS.1770).
TRUE PEAK: The maximum intersample peak level of an audio signal, required to prevent clipping in D/A conversion.
DYNAMIC RANGE: The ratio between the loudest and quietest parts of an audio signal, measured in dB. Higher DR = more expressiveness.
LOUDNESS WAR: The competitive escalation of master loudness (1990s–2010s) achieved through heavy limiting, reducing dynamic range.
TEMPORAL MASKING: The masking of a quiet sound by a louder sound that precedes (forward masking) or follows (backward masking) it in time.
SIMULTANEOUS MASKING: The masking of a target tone by a masker that occurs at the same time, spreading upward in frequency from the masker.
INTERAURAL LEVEL DIFF: The difference in sound pressure level between the two ears — a cue for horizontal sound localization, dominant at high frequencies.
INTERAURAL TIME DIFF: The difference in arrival time between the two ears — the primary localization cue at low frequencies (below ~1.5kHz).
COCKTAIL PARTY EFFECT: The ability to focus selective auditory attention on one sound source while filtering out others in a complex acoustic environment.
ABSOLUTE THRESHOLD: The minimum SPL required to detect a pure tone in a quiet environment, varying with frequency (lowest near 3–4kHz).

PSYCHOACOUSTICS LAB