submarine ping, stretching pitch

Hi

I'm working on that classic submarine ping sound. Traditionally this is 
created on analog synths by routing noise through an self oscillating 
filter. This also works nicely with lowresx, but my initial problem was 
that since the pitch of the sound is determined by the cutoff by the 
filter and other charastics of the filter the sound produced was 
microtonal. After playing a bit around I found out that if I use pitch 
to the power of two as input for the filter it's equal tempered.

So what I was hoping is that someone could explain why this is so? It 
works (which is nice) but I was frankly quite surprised...

Another small thing: There's click at the beginning of the sound. I 
imagine this comming from the initial wild state by the filter. Can this 
be avoided somehow (besides having a longer attack)?

Here's a small csd to demonstrate:

<CsoundSynthesizer>
<CsInstruments>
sr		=		44100
kr		=		4410
ksmps		=		10
nchnls		=		1

	instr 1	; ping
iamp		=		p4
ifreq		=		cpspch(p5)
itune		= 		.0000207
iattack		=		.001

aampenv		linseg		0, iattack, 1, p3 - iattack, 0
anoise		randi		iamp, 10000

afilt		lowresx		anoise, ifreq * ifreq * itune, 6, 3
afilt		balance		afilt, anoise

		out		afilt * aampenv
	endin
</CsInstruments>

<CsScore>
i1 0 3 10000 8.0
</CsScore>

</CsoundSynthesizer>


-- 
peace, love & harmony
Atte

http://www.atte.dk

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