.SH NAME
lab 3 \- create a filesystem, wavefs, that
serves a looped waveform.  This is our
staring point for playing with DSP.
.SH SETUP
Inferno 4th edition release 20040830. Using
.IR styxservers (2),
.IR audio (3),
.IR audio (6).
and Synthesis Toolkit in C++
<a href="http://ccrma.stanford.edu/software/stk">stk</a>.
Emu is running hosted on Windows XP.
(I haven't gotten the sound figured out yet using esd.)
.SH DESCRIPTION
I've been looking for tools to experiment with DSP.
The synthesis toolkit has a good all round collection 
of DSP routines and the code is easy enough to read.
I wanted this "sound workbench" well integrated with inferno.
Where possible make the resources files or file2chans.
.PP
The first step was to make a sound source; an oscillator.
For this I created a file server that serves two files
.IP
.EX
/ctl
/data
.EE
.PP
I started with the sample code from
.IR styxservers-nametree (2).
The server is given a raw audio file
to loop. I took the example raw files included
in the STK distribution. These are 16bit mono,
big-endian two's complement.
.PP
The data file served is an unlimited stream of
data in 16bit mono, little-endian, two's complement
suitable for streaming to
.B /dev/audio
.IP
.EX
% mkdir /mnt/dsp
% mount {wavefs sinewave.raw} /mnt/dsp
% echo rate 22050 > /dev/audioctl
% echo chans 1 > /dev/audioctl
% read 40000 < /mnt/dsp/wave > /dev/audio
.EE
.PP
Reading the ctl file describes attributes
of the sound file, similar to 
.B /dev/audioctl
Change attributes, such as pitch, by writing to 
.IR ctl . 
For example to create a sinewave rising in pitch
.IP
.EX
{for (i in `{seq 300 10 700}) {
	echo pitch $i > /n/dsp/wavectl; 
	read 4000 < /n/dsp/wave }
}> /dev/audio
.EE
.PP
.B seq 
is a port of the plan9 command.
.PP
I made some helper programs to look at the wave
form. 
.IP
.EX
% read < 100 /mnt/dsp/wave |pcm |gr
.EE
.PP
The
.B ffts
doesn't seem to work, or I misunderstand how to use it.
.SH CONCLUSION
These are the final versions:
<a href="http://caerwyn.home.comcast.net/lab/3/pcm.b">pcm.b</a>
<a href="http://caerwyn.home.comcast.net/lab/3/gr.b">gr.b</a>
<a href="http://caerwyn.home.comcast.net/lab/3/wavefs.b">wavefs.b</a>
<a href="http://caerwyn.home.comcast.net/lab/3/ffts.b">ffts.b</a>
<a href="http://caerwyn.home.comcast.net/lab/3/seq.b">seq.b</a>
And here is the sinewave from the STK package.
.EX
<a href="http://caerwyn.home.comcast.net/lab/3/sinewave.raw">sinwave.raw</a>
.EE
Given the above I have a model to build a family of
fileservers. Each serves a 
.I ctl
and 
.I data
file. 
Reading from 
.I data
always reads the sound samples in a format suitable
for
.B /dev/audio
and writing to
.I ctl
controls the effect, filter, or oscillator.
.PP
The filesystems can be layered. So a filter
is started by giving it as parameter the
wave file
.IP
.EX
% mount {wavefs sinewave.raw} /mnt/dsp
% mount {lowpfs /mnt/dsp/wave} /mnt/dsp
.EE
.PP
And so on.
It'll be interesting to see how layering filesystems
on a larger scale works out. 
A patch bay of filesystems may be required.
.PP
This is also an excuse to learn about DSP.