# 9 ways to NRT, part 6: Generative techniques with NRT and Csound

2015-01-11

Welcome to Part 6 of 9 Ways to NRT!

At this point, I've gone through many ways to translate NRT notation into useful formats, but I haven't yet shown how NRT can be used as composition tool for algorithmic and generative music. Today I wanted to write a simple generative music program using NRT and Csound.

The file below is a relatively simple pluck instrument I designed. Since we will be generating a corresponding score file, I've decided to do away with the monolithic format of the CSD and just use an oldschool .orc file. Save this file as plucker.orc:

sr	=	96000
ksmps	=	1
nchnls	=	2
0dbfs	=	1

instr 1	
icps = cpsmidinn(p4)
;random amplitude
iamp = random(0.2, 0.25)
;a pluck using a saw
a1 pluck iamp, icps, icps, ftgenonce(0, 0, 4096, 7, 1, 4096, -1), 1 
a1 *= linsegr(1, 1, 0)
;scoop out the low end
a1 = buthp(a1, 300)
outs a1, a1
endin

Now for the note generation. I'm using a mixture of awk and bash for my needs. The algorithm creates some nrt code by randomly stringing together smaller fragments of prewritten phrases in NRT. This code then gets sent to AWK where it is turned into a Csound score. The Csound score is then read and compiled to a wav file.

#!/bin/bash
tempo=120 

#collection of NRT fragments
cluster=(
 d4rm
 m4.f8s4
 t8Ds2. 
 m4rd
);

#randomly string NRT fragments, and generate score
for i in $(seq 1 4)
do 
nrt=$nrt${cluster[$RANDOM % 4]} 
done

echo $nrt | nrt -F ' ' |\
awk -vtempo=$tempo '
BEGIN{
ts = 60 / tempo
max = 0
}
{
 print "i1",$1 * ts,$2 * ts,$3 + 60;
 if($1 * ts + $2 * ts > max) {
     max = $1 * ts + $2 * ts
 }
}
' > score.sco

#render wav file
csound -o out.wav plucker.orc score.sco
rm score.sco

When this code is run, it creates a file called "out.wav", which can sound something like this