[sdiy] Prophet 5 noise sources

[Harry Bissell]

I'd have to check the REV3 layout, but its possible that they used two noise sources to eliminate having to route
the noise signal all over the PCB...

H^) harry



----- Original Message -----
From: Tom Wiltshire <tom at electricdruid.net>
To: Rutger Vlek <rutgervlek at gmail.com>
Cc: synthdiy diy <synth-diy at dropmix.xs4all.nl>
Sent: Sun, 13 Mar 2011 13:39:32 -0400 (EDT)
Subject: Re: [sdiy] Prophet 5 noise sources


On 13 Mar 2011, at 12:28, Rutger Vlek wrote:

>> So there you go! Between Rev 2 and Rev 3, Sequential decided it'd be a good idea to have independent noise sources for modulation and audio. God only knows why!
> 
> Perhaps they wanted to avoid modulation of an audio noise source with a predictable copy of itself (which might lead to strange effects).
> 
> Rutger

Perhaps. I suppose you could feed the noise source to the filter, and then modulate the filter cutoff with the same noise source from the wheel.
This is asking for another Pro-One experiment....one moment...
<short while later>
Yes, it looks like you might be right. If I use an external noise source to modulate the filter with the internal noise source fed through it, I get a hissy, noisy sound. If I also plug the external noise source into the audio input (so that the same source is used for audio and modulation) then the sound gets noticeably more "splattery". It's not a huge difference though.
Still, that's about the only situation I can see that the problem could arise, and I'm surprised they added a chip to improve one probably fairly littel-used sound. (Or are you all modulating your filters with noise sources all the time, and I'm just weird using envelopes?)

T.

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-- 
Harry Bissell & Nora Abdullah 4eva