ADSYN

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adsyn, pvoc

     ar   adsyn     kamod, kfmod, ksmod, ifilcod 
     ar   pvoc      ktimpnt, kfmod, ifilcod [, ispecwp]

DESCRIPTION

Output is an additive set of individually controlled sinusoids, using either an oscillator bank or phase vocoder resynthesis.

INITIALIZATION

ifilcod - integer or character-string denoting a control-file derived from analysis of an audio signal. An integer denotes the suffix of a file adsyn.m or pvoc.m; a character-string (in double quotes) gives a filename, optionally a full pathname. If not fullpath, the file is sought first in the current directory, then in the one given by the environment variable SADIR (if defined). adsyn control contains breakpoint amplitude- and frequency-envelope values organized for oscillator resynthesis, while pvoc control contains similar data organized for fft resynthesis. Memory usage depends on the size of the files involved, which are read and held entirely in memory during computation but are shared by multiple calls ( see also lpread).

ispecwp (optional) - if non-zero, attempts to preserve the spectral envelope while its frequency content is varied by kfmod. The default value is zero.

PERFORMANCE

adsyn synthesizes complex time-varying timbres through the method of additive synthesis. Any number of sinusoids, each individually controlled in frequency and amplitude, can be summed by high-speed arithmetic to produce a high-fidelity result.

Component sinusoids are described by a control file describing amplitude and frequency tracks in millisecond breakpoint fashion. Tracks are defined by sequences of 16-bit binary integers:

-1, time, amp, time, amp,...

-2, time, freq, time, freq,...

such as from hetrodyne filter analysis of an audio file. ( For details see the Appendix on hetro.) The instantaneous amplitude and frequency values are used by an internal fixed-point oscillator that adds each active partial into an accumulated output signal. While there is a practical limit (currently 50) on the number of contributing partials, there is no restriction on their behavior over time. Any sound that can be described in terms of the behavior of sinusoids can be synthesized by adsyn alone.

Sound described by an adsyn control file can also be modified during re-synthesis. The signals kamod, kfmod, ksmod will modify the amplitude, frequency, and speed of contributing partials. These are multiplying factors, with kfmod modifying the cps frequency and ksmod modifying the speed with which the millisecond bread-point line-segments are traversed. Thus .7, 1.5, and 2 will give rise to a softer sound, a perfect fifth higher, but only half as long. The values 1,1,1 will leave the sound unmodified. Each of these inputs can be a control signal.

pvoc implements signal reconstruction using an fft-based phase vocoder. The control data stems from a precomputed analysis file with a known frame rate. The passage of time through this file is specified by ktimpnt, which represents the time in seconds. ktimpnt must always be positive, but can move forwards or backwards in time, be stationary or discontinuous, as a pointer into the analysis file. kfmod is a control-rate transposition factor: a value of 1 incurs no transposition, 1.5 transposes up a perfect fifth, and .5 down an octave.

This implementation of pvoc was written by Dan Ellis. It is based in part on the system of Mark Dolson, but the pre-analysis concept is new.

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