.SH NAME
lab 7 - sequencer; create a simple sequencer that can play
back a subset of SKINI messages.
.SH SETUP
Inferno 4th Edition release 20040830.
.SH DESCRIPTION
.SS "2004/0928 20:37
.I SKINI 
is the sequencing language from the STK.
It is a readable form of MIDI, and was designed
to be "extensable and hackable"; all of which
make it ideally suited to this application and Inferno.
Here is a brief example
.IP
.EX
// Measure number 1	=0
NoteOn   	0.416667     2	  72	  64
NoteOff  	0.208333     2	  72	  64
NoteOn   	0            2	  71	  64
NoteOff  	0.208333     2	  71	  64
NoteOn   	0            2	  72	  64
NoteOff  	0.416667     2	  72	  64
NoteOn   	0            2	  67	  64
NoteOff  	0.416667     2	  67	  64
.EE
.PP
There is one command per line. The line begins
with command name followed by parameters
separated by space or tabs. The second parameter
is always the time delta. For the 
.I NoteOn
command, the third argument is channel (or voice),
fourth is midi pitch, and fifth if velocity (I guess! I'm ignoring it for now).
.PP
These SKINI messages are interpreted by 
.IR sequencer ,
which sends messages to one or more instruments and reads
back audio data.
.PP
I created a basic instrument module, which should
be used as a template for later instruments,
called
.IR simple .
It uses the
.I adsr
and 
.I wave
modules.
.PP
The
.I wave
module I have described previously.
.I Adsr
is a standard Attack, Decay, Sustain,
Release envelope. I copied the implementation
from the STK.
.PP
.I Simple
and
.I sequencer
use a new interface to assist
in using other signal sources.
.IP
.EX
Sig: adt {
	ctl: ref Sys->FD;
	data: ref Sys->FD;
		
	open: fn(s: string): ref Sig;
	read: fn(s: self ref Sig, nsamples: int): array of real;
	readbytes: fn(s: self ref Sig, nbyte: int): array of byte;
};
.EE
.PP
This will evolve. It is currently part of the 
.I dsp
module.
.PP
The source signals are opened by
.I init.
I made a small modification to
.B signalfs.b
moving the 
.I init
call from 
.B signalfs.b:/serve
to
.B signalfs.b:/requestproc
to avoid deadlock.
.PP
I created 
.B /mnt/dsp
for mounting
.I signalfs
and
.B /mnt/dsp/raw
because I am hardcoding the names of some signal sources and
raw sound files.
The raw files from the STK should be bound or copied to
.BR /mnt/dsp/raw . 
Therefore start as
.IP
.EX
% bind /n/j/stk-4.1.3/rawwaves /mnt/dsp/raw
% signalfs -a /mnt/dsp
.EE
.PP
Setup the modules and /dev/audio
.IP
.EX
% bind -a '#A' /dev
% echo rate 22050 > /dev/audioctl
% echo chans 1 > /dev/audioctl
% echo add wave.dis wave > /mnt/dsp/ctl
% echo add adsr.dis adsr > /mnt/dsp/ctl
% echo add simple.dis simple > /mnt/dsp/ctl
.EE
.PP
Run a SKINI file.
.IP
.EX
% sequencer /mnt/dsp/simple < bachfugue.ski > /dev/audio
.EE
.PP
The sequencer assumes 4 voices currently.
It's very basic; just for testing while creating new instruments.
It will most surely be rewritten.
.SH CONCLUSION
Here are the latest.
<a href="http://caerwyn.home.comcast.net/lab/7/adsr.b">adsr.b</a>
<a href="http://caerwyn.home.comcast.net/lab/7/bachfugue.ski">bachfugue.ski</a>
<a href="http://caerwyn.home.comcast.net/lab/7/dsp.b">dsp.b</a>
<a href="http://caerwyn.home.comcast.net/lab/7/dsp.m">dsp.m</a>
<a href="http://caerwyn.home.comcast.net/lab/7/sequencer.b">sequencer.b</a>
<a href="http://caerwyn.home.comcast.net/lab/7/signal.m">signal.m</a>
<a href="http://caerwyn.home.comcast.net/lab/7/signalfs.b">signalfs.b</a>
<a href="http://caerwyn.home.comcast.net/lab/7/simple.b">simple.b</a>
<a href="http://caerwyn.home.comcast.net/lab/7/wave.b">wave.b</a>
The SKINI language has more commands and features
than implemented here.
.PP
Again, it is slow. I should buffer writes to the /dev/audio,
maybe a few seconds worth, so the audio sounds smooth.
Otherwise, I need to write to a file first then stream the
file to
.B /dev/audio.
However, It's enough for testing while creating some of the more complex
instruments from the STK.
.PP
The sequencer could be a module of signalfs like any other.
Reads of the
.I data
return the audio data. The 
.I ctl
file is a synthetic file which could be edited within
any editor. But this is a slightly different interface
than other signals. An alternative is to use the
skini file as a source file just like the raw files for the wave module.
The sequencer module then represents patterns,
which can be combined, looped, and sequenced just
like any other signal.
.SH "DAY DREAMING
I can have a grid generating the sounds. 
What is possible with unlimited cpu power?
Using a grid we should
be able to create, in realtime, a very complex
syntesized soundscape.
Could we use the plan9 grid for this?
Run emu on each node, serve a signalfs, 
bind them all into a local namespace, then generate
the patterns. 8 channel, 24 bit, unlimited voice 
and polyphony.

.SH REFERENCES
STK is now a link on the side bar.