Auditory Distortion Product Research Articles

CONCEPTUAL MUSIC: NEW MEDIA AND FRONTIERS IN MARYANNE AMACHER’S CITY-LINKS SERIES

AbstractBetween 1967 and 1988 Maryanne Amacher's City-Links series comprised radio broadcasts, sound installations and interdisciplinary performances featuring her practice of mixing sonic material from multiple remote locations joined via telecommunications infrastructure. These works reflect Amacher's compositional elevation of the process of sonic perception alongside musical material, an approach that would evolve to inform her later work in which she dealt with the musical potential of psychoacoustic phenomena known as auditory distortion products. This article aims to provide an overview of the City-Links series as a unique product of the experimentation in post-war avant-garde music and visual and conceptual art. After a synopsis of Amacher's early compositional development, I offer a comparison between Amacher's City-Links and John Cage's radio works, exploring different contemporary approaches to transmission and broadcast as a compositional medium. I then situate the site-specificity of the City-Links works within the extramusical frame offered by Amacher's contemporary Robert Smithson's site/non-site dialectic. The article finally suggests the necessity for a more holistic examination of Amacher's legacy that accounts for both the musicological and art-historical implications of her work.

Discrimination bandwidths for amplitude modulated and quasi-frequency modulated tones with spectral cues degraded by a roving-level.

Theoretically, discriminating an amplitude modulated tone (AM) from a quasi-frequency modulated tone (QFM) is an ideal task for measuring the bandwidth of phase sensitivity because the stimuli have identical amplitude spectra but different phase spectra. The stimuli are perfectly discriminable at narrow bandwidths, but become indistinguishable at wide bandwidths. Measurements, however, are thought to be compromised by auditory distortion products, particularly a cubic distortion tone which interacts with the lower sideband of the stimulus to create an intensity cue. The results and implications of using a roving level procedure to eliminate distortion product effects are discussed.

Evaluation of complex stimuli and resulting distortion product spectrum in auditory distortion product synthesis

Auditory distortion products are frequency components produced within the listener’s ears upon the presentation of simultaneously sounding stimulus tones. Under certain conditions the listener can perceive distortion products as additional frequencies not present in the acoustic space, and the tones appear to be localized within the head. Musicians have been aware of this phenomenon of “combination tones” since the 18th century, but advancements in technology allow for new possibilities in music synthesis. On the Sensations of Tone is a series of compositions featuring a separate stream of musical material generated as auditory distortion products. The pieces are built using The Ear Tone Toolbox, a collection of open-source instruments for producing combination tones. While a single pair of stimulus frequencies typically elicits a small number of perceivable distortion products, the author puts forth a technique for evoking a spectrum of distortion products using a greater number of frequencies. The technique is informed by a mathematical model and is the basis of the next version of The Ear Tone Toolbox. This talk will provide an overview of the updated software, model, and compositions in the series.

Isolating spectral cues in amplitude and quasi-frequency modulation discrimination by reducing stimulus duration

This study investigated the psychophysical effects of distortion products in a listening task traditionally used to estimate the bandwidth of phase sensitivity. For a 2000 Hz carrier, estimates of modulation depth necessary to discriminate amplitude modulated (AM) tones and quasi-frequency modulated (QFM) were measured in a two interval forced choice task as a function modulation frequency. Temporal modulation transfer functions were often non-monotonic at modulation frequencies above 300 Hz. This was likely to be due to a spectral cue arising from the interaction of auditory distortion products and the lower sideband of the stimulus complex. When the stimulus duration was decreased from 200 ms to 20 ms, thresholds for low-frequency modulators rose to near-chance levels, whereas thresholds in the region of non-monotonicities were less affected. The decrease in stimulus duration appears to hinder the listener's ability to use temporal cues in order to discriminate between AM and QFM, whereas spectral information derived from distortion product cues appears more resilient.

The inner ear as a musical instrument

This paper addresses the place of the ears and their potential as musical instruments. Psychoacoustics research into the non-linearities of the inner ear has proven that the organ has much more to offer the composer than has been previously considered. By reversing the role of the ear from being a submissive receiver to an active participant in the creative process, an exciting level of opportunity opens up for the composer. A focus is given in this paper to bandwidth phenomena and auditory distortion products with references to the author's own compositional material which seeks to highlight that the investigation of the non-linear nature of the inner ear is revolutionary in relation to the place of the ear within contemporary composition. Central to this work is the notion that the ear is not simply a passive component of the musical experience. Adorno once stated that the ear is a “dozy and inert” organ and by disproving such a view one can destabilize common assumptions about psychoacoustics and the potential of the ears as musical instruments.

Sound Synthesis with Auditory Distortion Products

Abstract This article describes methods of sound synthesis based on auditory distortion products, often called combination tones. In 1856, Helmholtz was the first to identify sum and difference tones as products of auditory distortion. Today this phenomenon is well studied in the context of otoacoustic emissions, and the “distortion” is understood as a product of what is termed the cochlear amplifier. These tones have had a rich history in the music of improvisers and drone artists. Until now, the use of distortion tones in technological music has largely been rudimentary and dependent on very high amplitudes in order for the distortion products to be heard by audiences. Discussed here are synthesis methods to render these tones more easily audible and lend them the dynamic properties of traditional acoustic sound, thus making auditory distortion a practical domain for sound synthesis. An adaptation of single-sideband synthesis is particularly effective for capturing the dynamic properties of audio inputs in real time. Also presented is an analytic solution for matching up to four harmonics of a target spectrum. Most interestingly, the spatial imagery produced by these techniques is very distinctive, and over loudspeakers the normal assumptions of spatial hearing do not apply. Audio examples are provided that illustrate the discussion.

Binaural detection with spectrally nonoverlapping signals and maskers.

Thresholds were measured for diotic tonal signals masked by interaurally delayed bands of Gaussian noise. When the signal frequency was 525 Hz, the spectrum of the masker was either below (highest frequency, 450 Hz) or above (lowest frequency, 600 Hz) the frequency of the signal. With a 450‐Hz signal, the spectrum of the masker was always above the signal frequency (lowest frequency, 600 Hz). Signals had a 250‐ms duration and were temporally centered within 300‐ms‐long maskers. The spectrum level of the maskers was 60 dB. Masked thresholds obtained in all three conditions varied sinusoidally with the interaural delay of the masker. The periodicities within the data were close to, but not identical with, the periodicities of the signals (not the maskers). This outcome is discussed in terms of (1) auditory distortion products stemming from interactions within the masking bands of noise [cf. van der Heijden and Kohlrausch, J. Acoust. Soc. Am. 98, 3125–3134 (1995)], and (2) binaural models incorporating internal delay mechanisms. It is shown that using such spectrally nonoverlapping signals and maskers can help test interesting hypotheses concerning binaural models. [Work supported by Grant No. 5 RO1 DC00234‐13 from the National Institute of Deafness and other Communication Disorders, NIH.]

Auditory Distortion Products Measured With Averaged Auditory Evoked Potentials

The purpose of this investigation was to describe the properties of averaged auditory evoked potential distortion products (AEP-DPs) in guinea pigs. This study provided a step toward developing a clinical index of nonlinear processing of auditory signals and supplied a baseline for studies evaluating the effect of cochlear damage on AEP-DPs. The amplitude of the AEP-DPs was evaluated as a function of f2/f1 ratio (1.12-1.52) and primary frequency (500 Hz-2000 Hz). The amplitude of the AEP cubic difference tone (AEP-CDT) increased with increasing f2/f1 ratio for the 500-Hz f1 primary and remained constant for the 800-Hz and 1700-Hz f1 primaries. The AEP-CDT generated by the 1100-Hz and 1400-Hz f1 primaries was maximum for the middle f2/f1 ratios (1.22, 1.32, and 1.42). The AEP-CDT could not be distinguished from the noise floor for the 2000-Hz f1 primary. The AEP difference tone (AEP-DT) was larger and more frequently identified than the AEP-CDT. The amplitude of the AEP-DT decreased with an increase in f2/f1 ratio. The decrease was more pronounced for low-frequency f1 primaries than for high-frequency f1 primaries.

Auditory distortion products as predictors of TTS: A final look

There is a long history suggesting a relation between the nonlinear amplitude response of the auditory system, physical overload, and the development of threshold shift. In a previous report, I showed a relation in three subjects between TTS2 and the amplitude of the distortion product ∫1 + ∫2 measured behaviorally. This relation has been examined more fully in a population of 20 listeners. Complete data were obtained in 13 of these listeners. The relation between TTS2 and the amplitude of the ∫1 + ∫2 and 2∫1 + ∫2 was examined at ∫1 = 500, 1000, and 2000 Hz. Distortion product amplitudes were measured for ∫1 and ∫2 = 1.2∫1, each at 70 dB SPL. TTS2 was measured at 1.5∫1 for pure tones at ∫1, either at 90 or 100 dB SPL. Results are mixed. For a 1‐kHz fatiguer, a relation exists between distortion product amplitude and TTS2. The relation is TTS2 = 0.25 ADP‐1.2 with r = 0.52. This may not be meaningful. At 500 Hz, no TTS was produced by the exposures although there was variability in the level of ∫1 + ∫2 betw...

Nonmonotonic behavior of distortion product 2f1-f2: psychophysical observations.

A detailed study was made of the amplitude and phase characteristics of auditory distortion product 2f1−f2 in the neighborhood of an amplitude minimum. For f2=1.0, 1.2, and 1.4 kHz, f1 was varied from 0.68⋅f2 to 0.88⋅f2, and the (equal) intensity of the two primary tones was varied from 50 to 70 dB SPL. For the one subject investigated, the ampltiude of the 2f1−f2 distortion product exhibited a single minimum in the portion of the f1/f2 versus intensity plane explored. The value of f1/f2 at the minimum was 0.8 and was roughly constant for various frequencies of f2. The primary-tone amplitude at the minimum decreased with increasing f2 from 60 dB SPL at 1 kHz to less than 50 dB SPL at 1.4 kHz. The 2f1−f2 phase in the neighborhood of the null was complicated. It changed abruptly at the minimum, it changed more rapidly with f1/f2 at primary-tone intensities below the null than above, and it changed slowly with primary-tone intensity at f1/f2 ratios both below and above the null. Therefore, a complete circuit around the null in the f1/f2 versus intensity plane resulted in a change of 2f1−f2 phase of 360°. Subject Classification: 65.56.

Nonmonotonic behavior of distortion product 2f1 − f2: psychophysical observations

A detailed study was made of the amplitude and phase characteristics of auditory distortion product 2f1 − f2 in the neighborhood of an amplitude minimum. For f2 = 1.0, 1.2, and 1.4 kHz, f1 was varied from 0.68⋅f2 to 0.88⋅f2, and the (equal) intensity of the two primary tones was varied from 50 to 70 dB SPL. For the one subject investigated, the amplitude of the 2f1 − f2 distortion product exhibited a single mimimum in the portion of the f1/f2 vs intensity plane explored. The value of f1/f2 at the minimum was 0.8 and was roughly constant for various frequencies of f2. The primary-tone amplitude at the minimum decreased with increasing f2 from 60 dB SPL at 1 kHz to less than 50 dB SPL at 1.4 kHz. The 2f1 − f2 phase in the neighborhood of the null was complicated. It changed abruptly at the minimum, it changed more rapidly with f1/f2 at primary-tone intensities below the null than above, and it changed slowly with primary-tone intensity at f1/f2 ratios both below and above the null. Therefore, a complete circuit around the null in the f1/f2 vs intensity plane resulted in a change of 2f1 − f2 phase of 360°.