NAME

lab 4 - signalfs; generalize wavefs to a family of file servers that support a variety of sound sources and filters.

SETUP

Inferno 4th edition release 20040830. Using wavefs and the Synthesis Toolkit in C++.

DESCRIPTION

I started with the wavefs source and abstracted out an interface for modules that the fileserver can call. The signal processor implements this interface. The compiled dis module that implements a specific dsp is passed as parameter to the signalfs which exports the standard files .IP 

/signal
/signalctl

The interface is quite simple .IP 

Signal: module {
	configstr: string;


	init:	fn(args: list of string);
	config: fn(s: string);
	tickFrame: fn(): array of real;
};

Messages written to /signalctl are passed to config , and reads return the contents of Signal.configstr . Reads from /signal , which is readonly, are sent data generated by tickFrame . I rewrote the wave loop module using this interface. wave.b The server is now mounted as .IP 

% mount {signalfs wave.dis sinewave.raw} /mnt/dsp/wave
% lc /mnt/dsp/wave
signal    signalctl

I implemented a few other DSPs. noise.b envelope.b filter.b The original source for all of these is from the STK. Each signal has it's own config options. Here's an example using the filter .IP 

% mount {signalfs filter.dis} dsp/filter
% echo acoef 1.0 0.1 0.5 > dsp/filter/signalctl
% echo bcoef 0.5 0.5 > dsp/filter/signalctl
% echo source dsp/wave/signal
% cat dsp/filter/signalctl
rate 22050
chans 1
gain 1
source dsp/wave/signal
acoef 1 .1 .5 
bcoef .5 .5 
% read 40000 < dsp/filter/signal > /dev/audio

CONCLUSION

It is too slow. We need another iteration to read vectors of ticks instead of single ticks.

I like the layout. It is simple to add new filters and sources. A filter can be applied to another signal file by just writing to the control file.

We'll need a mixerfs or voicefs to combine many voices and something to do the sequencing. It's nice generating sounds from the shell.

REFERENCES

Cook, Perry and Scavone, Gary P. "Synthesis Toolkit in C++ " http://www-ccrma.stanford.edu/software/stk/