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		NSF  Proposal

	Computer Simulation of Natural Auditory Signals
		and Reverberant Spaces
I.	Introduction

In recent years there have been significant advances in computer simulation
and analysis of complex auditory signals.  On the one hand, the use of the computer
has demonstrated the extraordinary complexity of natural sounds and consequent
difficulty in understanding, and on the other, the computer has provided
the means of implementation of powerful synthesis and analytical techniques.

At the Stanford Artificial Intelligence Laboratory programs and techniques
have been developed over a period of ten years, for the simulation of moving
sound sources in reverberant spaces and for the analysis and synthesis of 
complex signals, some of which are startlingly simple in implementation and
novel in conception.  The progress of this research has certainly been enhanced
by the high level of technological expertise which characterizes the
inter-disciplinary environment of the Artificial Intelligence Labotratory.

Audio signals are generated by a PDP-10 computer which has a 4-channel D-A
converter for analog conversion of the sampled waveform.
The analysis is accomplished by means of an A-D converter which converts
audio input into a sampled wave which is stored on a disk for processing.
The programs forthe synthesis of wave-forms are based on the acoustical
compiler developed by M.V. Mathews at Bell Telephone Laboratories
adapted to the time-sharing, interactive capabilities of the PDP-10 system,
while the wave analysis programs were written by J.A. Moorer of Stanford.


Proposed Research-

1.  Analysis and Synthesis of Music-Instrument Tones and the Singing Voice-

The time-variant properties of natural sound in
both the frequency and amplitude domaines have been shown to be of
critical importance in the perception of timbre or tone-color.  Programs and
techniques are being developed for the analysis and synthesis
of acoustical signals which represent these time-variant properties in
the form of spectral plots.  The frequency and amplitude data is then reduced
to its minimum without disturbing the original perceptual image.  Subjective
judgements are made by musically trained listeners. Manipulation of the
simplified data in conjunction with multi-dimensiional scaling techniques
of judgements, suggests the critical subjective cues for the various
categories of timbre.

2.  The Synthesis of Complex Spectra by Means of Frequency Modulation-