Hirofumi Yanagawa

Sound field control system for a multi-speaker system

A plurality of reverberation signal generating circuits are provided for generating a plurality of reverberation signals from input audio signals of two channels. Each of the reverberation signals has a predetermined function of correlation. A pair of filters are provided for controlling the function of correlation of the reverberation signal and for applying controlled reverberation signals to reverberation speakers, thereby providing a sound field.

Method and apparatus for erasing acoustic echo

An acoustic echo erasing apparatus which generates a pseudo-echo component from an audio reception signal (a vector x1) using an adaptive filter, and removes the pseudo-echo component from an audio transmission signal (a vector y). The apparatus extracts a feedback component depending only on the audio reception signal from the audio transmission signal, and passes the audio reception signal through the adaptive filter to generate the pseudo-echo component while setting a transfer characteristic of the adaptive filter in accordance with the feedback component.

The Pioneer sound field control system at the University of Aizu Multimedia Center

The PSFC, or Pioneer sound field control system, is a DSP-driven hemispherical 14-loudspeaker array, installed at the University of Aizu Multimedia Center. Collocated with a large screen rear-projection stereographic display the PSFC features realtime control of virtual room characteristics and direction of two separate sound channels, smoothly steering them around a configurable soundscape. The PSFC controls an entire sound field, including sound direction, virtual distance, and simulated environment (reverb level, room size and liveness) for each source. It can also configure a dry (DSP-less) switching matrix for direct directionalization. The PSFC speaker dome is about 14 m in diameter, allowing about twenty users at once to comfortably stand or sit near its sweet spot.

Acoustic echo cancellation by short‐time Fourier transform and cross‐spectrum processing.

Acoustic echo cancellers have problems in estimating room transfer functions (TFs) for acoustic echo paths when the conditions are noisy in the acoustic space. In this article, the possibility of estimating the room TFs is investigated by taking a time‐frame‐averaged cross spectrum(CS) between the input signals and error signals, which are composed of echo signals through the echo path and the surrounding noise. First, the short‐time Fourier transforms (STFTs) and cross spectrum for both the input and error signals are taken. The TFs can be estimated from the ratio of the CS to the power spectrum of the input signal, since it can be expected that the time‐frame‐averaged CS components between the input signal and the surrounding noise will be zero. It was reconfirmed by computer simulation that the echo signals can be suppressed as the averaging process goes on, even in noisy conditions. The room TFs could be estimated as long as the S/N ratio was about 10 dB. This STFT‐CS method requires more calculations...

Sound‐image broadening by a single echo and its relation to the transient interaural cross‐correlation function

The sounds reproduced by two loudspeakers often consist of a preceding sound and its echo when the listener’s position is offset like the position of a driver when listening to a car stereo. Consequently, the sound image is broadened by the echo. In this article, the width of the sound image produced by the preceding sound and the echo under a loudness balance condition were examined. TRICC (the maximum value of the transient interaural cross‐correlation function) was then applied to analyze such sound image broadening. In hearing experiments, a pair of noise bursts was used as a model of transient sound, such as speeches and musical sounds. A pointer noise (a pair of noises with correlation coefficients) was used to express the width of the sound image. The experiments showed that the width of the sound image increases as delay time between the preceding sound and the echo increases. When the delay time becomes longer than 10 ms, the width of the sound image corresponds to the value of the interaural cor...

Improvement of the accuracy of attenuation constant estimation using the cross spectral technique

This paper proposes a method to improve the accuracy of the attenuation constant estimate obtained using the cross-spectral technique. In the cross-spectral technique, the envelope of the estimated impulse response is deformed due to the use of a time window. As a result, the estimated impulse response decays more rapidly than the real impulse response does and the attenuation constant obtained by the estimated impulse response becomes larger than the real value. This paper explains first how the attenuation constant changes in the process of impulse response estimation, next, the proposed method for improving the estimation accuracy.