[sdiy] Prophet 5 noise sources

[Richard Atkinson]

http://www.youtube.com/watch?v=Z9O2tsIbKD0

This is "Careering" by Public Image Limited. Notice Keith Levene playing the 
rev 2 Prophet-5 as well as his Travis Bean Wedge.

The technical manual confirms that the rev 2 Prophet has an MN5837 noise 
generator.

MN5837 noise sounds alright to me!


--------------------------------------------------
From: "Tom Wiltshire" <tom at electricdruid.net>
Sent: Sunday, March 13, 2011 1:41 AM
To: "Neil Johnson" <neil.johnson97 at ntlworld.com>
Cc: "'synthdiy diy'" <synth-diy at dropmix.xs4all.nl>
Subject: Re: [sdiy] Prophet 5 noise sources

>
> On 12 Mar 2011, at 22:06, Neil Johnson wrote:
>
>> Jay,
>>
>>> Were both clocked at the same rate?
>>>
>>> I could see having a noise source for modulation being slower than one 
>>> for
>>> audio?
>>
>> The MN5837 has an internal clock source, so you have no control over it 
>> whatsoever (other than perhaps varying the supply voltage, which *might* 
>> change the internal clock frequency).
>>
>> You apply power and ground, and out comes the SCHUFFSCHUFFSCHUFFSCHUFF..
>>
>> Neil
>
> My understanding from the datasheet was that changing the supply voltage 
> does change the clock frequency, pretty directly. Going back over it I 
> don't actually see where I got that idea from. Anyway, the gist of it is 
> that it covers the full range from "bad" to "dreadful", with clock 
> frequencies from 24 to 56KHz. The cycle time is given as 1.1 to 2.4 
> seconds - No, it is, honestly. Seriously. You can check if you don't 
> believe me;
>
> http://pdf1.alldatasheet.com/datasheet-pdf/view/9284/NSC/MM5837.html
>
> I did think it was significant that the Prophet rolls off the high end for 
> noise modulation though. Significant enough that I went and tried it with 
> a noise source both with and without a 100K/100n filter, feeding the 
> result into my Pro-One (close enough to a Rev 3 Prophet voice). To be 
> honest, I couldn't really hear much difference. I was expecting the 
> filtered version to be "smoother" or "tamer" or some such, but if it is, I 
> can't really hear it. Not that my hearing is anything to write home about, 
> but then, neither is most people's. So I'd like to hear the rationale 
> behind the decision to use pink noise for the wheel mod, rather than the 
> white source directly.
> It might have something to do with DC levels, since my PIC noise source 
> kicks out a random signal from 0-5V, which means there's an average 2.5V 
> DC level hiding in there. I suspect the MN5837 does similar. However, 
> you'd be looking at highpass filtering to remove that, not lowpass 
> filtering, so I still don't know what they had in mind.
>
> T.
>
>
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