Analysis with binaural auditory model and experiment on the timbre of Ambisonics recording and reproduction

A scheme for analyzing the timbre in spatial sound with binaural auditory model is proposed and the Ambisonics is taken as an example for analysis. Ambisonics is a spatial sound system based on physical sound field reconstruction. The errors and timbre colorations in the final reconstructed sound field depend on the spatial aliasing errors on both the recording and reproducing stages of Ambisonics. The binaural loudness level spectra in Ambisonics recon- struction is calculated by using Moore＇s revised loudness model and then compared with the result of real sound source, so as to evaluate the timbre coloration in Ambisonics quantitatively. The results indicate that, in the case of ideal ＇independent signals, the high-frequency limit and radius of region without perceived timbre coloration increase with the order of Ambisonics. On the other hand, in the case of recording by microphone array, once the high-frequency limit of microphone array exceeds that of sound field reconstruction, array recording influences little on the binaural loudness level spectra and thus timbre in final reconstruction up to the high- frequency limit of reproduction. Based on the binaural auditory model analysis, a scheme for optimizing design of Ambisonics recording and reproduction is also suggested. The subjective experiment yields consistent results with those of binaural model, thus verifies the effectiveness of the model analysis.

Temporal sequential correlation analysis on compoundaction potentials of the auditory nerve versus the stimulating AM-sound envelope

Compound action potentials of the auditory nerve in response to amplitude modulating tones were recorded in guinea pigs with electrode implanted to the exit of the internal auditory meatus and temporal sequential correlation between the responses and the modulators was studied in a paradigm of systematically changing acoustic parameters. Three kinds of modulators were used. continuous or burst sinusoids of fixed frequency (in the range of 40 Hz-5 kHz), short bursts of sinusoids with changing frequency and short segments of speech signal. Ranges of parametric variation were 500 Hz-20 kHz for carrier frequency, 5%-95% for modulation depth and 20 dB-90 dB SPL for intensity. For continuous or burst sinusoidal modulators of fixed frequencies, the correlation coefficient (r) remained quite high in most parametric conditions, ranging from 0.80 to 0.95. It became smaller mainly in instances of decreased response amplitude on account of unfavourable parameters. For burst modulators of changing frequency, r varied around 0.66-0.86. When segments of speech signal served as the modulators, significant correlation (r around 0.50 ) also existed, indicating the validity of the timing mode of information encoding for speech sound at the cochlear nerve level. Some theoretical and technical points in studying the timing mechanism of audition is discussed.

Soundscapes and the sense of hearing of fishes

Underwater soundscapes have probably played an important role in the adaptation of ears and auditory systems of fishes throughout evolutionary time,and for all species.These sounds probably contain important information about the environment and about most objects and events that confront the receiving fish so that appropriate be-havior is possible.For example,the sounds from reefs appear to be used by at least some fishes for their orientation and migration.These sorts of environmental sounds should be considered much like“acoustic daylight,”that continuously bathes all environments and contain information that all organisms can potentially use to form a sort of image of the environment.At present,however,we are generally ignorant of the nature of ambient sound fields impinging on fishes,and the adaptive value of processing these fields to resolve the multiple sources of sound.Our field has focused almost exclusively on the adaptive value of processing species-specific communication sounds,and has not considered the informational value of ambient“noise.”Since all fishes can detect and process acoustic particle motion,including the directional characteristics of this motion,underwater sound fields are potentially more complex and information-rich than terrestrial acoustic environments.The capacities of one fish species(goldfish)to receive and make use of such sound source information have been demonstrated(sound source seg-regation and auditory scene analysis),and it is suggested that all vertebrate species have this capacity.A call is made to better understand underwater soundscapes,and the associated behaviors they determine in fishes.