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Do I need multiple noise sources with multiple S&H?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion Goto page 1, 2  Next [all]
Author Do I need multiple noise sources with multiple S&H?
akavalve
If I trigger 2 (or more) S&H modules from the same trigger source but want them to output different random voltages do I need to use two (or more) noise sources?

I'm assuming yes. Just wondering is there are any other ( i.e. cheaper in terms of $ and hp) options.
kcd06
Presuming I understand you, I would think the answer is no, assuming that your S&H modules are /not/ set to sample their input at the same rate and time. If they are not working in lockstep, they are sampling the input at different points, and get different answers. If they are synchronized, then you would, I think, need different input streams for each. Or, offset the input, run it through a filter or other delay, which would effectively give you a new signal for your S&H modules....


Edited to add: I've not tried this--I have only one S&H--but I would guess that you would have a hell of a time synchronizing two S&H modules by hand working from a noise source, so in practice it wouldnt really matter.
mskala
Two identical S&H units with the same voltage input and the same trigger input, would be expected to produce the same output. So you need two different noise sources; two different trigger sources; or (as kcd06 said) to process the noise in some way that is different for the two S&H units.
akavalve
That's what I figured. Thanks for the confirmation.
magnetsandlasers
Gives me an idea to try this, running one of the noise outputs through a filter.
PrimateSynthesis
akavalve wrote:
If I trigger 2 (or more) S&H modules from the same trigger source but want them to output different random voltages do I need to use two (or more) noise sources?


You only need to mult it, then change it slightly in some way such scaling, offset, etc. Inversion, delay, shifting the phase (run it through an unmodulated all-pass) would give you different voltages but with the same range and distribution (as opposed to pass filtering, addition, multiplication, etc.)
ranix
It's good to have two independent noise sources available I think. I have one dedicated noise source and one module that produces digital noise. By mixing the two I can generate as many mostly-independent noise sources as required.
Dave Peck
I have two S/H modules that I often clock together from one clock and I generate two different random stepped signals just by using the white noise output as the input to one S/H and the pink noise output as input to the other S/H.

If your noise gen only has one output, you can create a second random signal for the second S/H by doing just about anything to alter the tone of the noise generators audio signal at all, like passing it through a spare filter (even if the cutoff is set high so it doesn't seem to change the sound of the noise), or a spare distortion module, or a phaser, or a slew set to a very fast rate, etc.

An offset may not work well because the audio signal will remain unaltered except for the DC offset so the second S/H will still produce the same steps as the first S/H, just with a higher voltage offset.
tnktni
I imagine some filtering of the noise on one signal source would do the trick. Might also work if you run it through a wavefolder/distortion module?
luketeaford
Mixing in a little bit of audio or LFO should work, too.

A very slight trigger delay should work.

Slew the noise signal (essentially the same as the filter idea, but I have more slews than dedicated filters).
BenJBX
It's an interesting question. I think that even if two separate s&h modules had a common source and clock, it's unlikely they would produce identical output waves because of tiny timing differences in trigger propogation, internal circuit delays and thresholds and so on. I've never actually tried though so I'll do that next time I'm in the studio.
Operator One
I would use a multiples and change slightly the settings of every S&H to achieve differente types of sounds.
diophantine
BenJBX wrote:
It's an interesting question. I think that even if two separate s&h modules had a common source and clock, it's unlikely they would produce identical output waves because of tiny timing differences in trigger propogation, internal circuit delays and thresholds and so on. I've never actually tried though so I'll do that next time I'm in the studio.

Bingo.

To verify I just tested the dual S&H on my Steiner-Parker Synthasystem. Same circuits, same component lots, same external white noise source, same external trigger source. The output of the two S&H circuits were completely different from each other every time. Tested it both "by ear" and with a voltmeter.
cptnal
Tried this myself off the back of this thread with my A148 (both halves set to S&H) and they were pretty much matching each other. Which surprised me. Like BenJBX I reckoned there would be enough natural variation for them to produce different results. I guess not.
thumbs up
Dcramer
Keep in mind that when you sample noise in order to produce clocked Random voltages, what the S&H module grabs is the instantaneous voltage level of the noise at that moment.
Altering the over gain of the noise, and offsetting it should have a bigger difference than effects that might alter its perceived timbre as the peak to peak voltage present in the noise may not change much. thumbs up
wechard
Just to add another data point — I tried this with my 2hp dual S&H and the outputs were nearly identical about half the time, a bit detuned about a quarter of the time, and quite far apart for the other quarter.
Dave Peck
Yes, the more high frequency content the noise source has, the more likely it will be that the two S/H modules will produce different stepped levels even when clocked from the same clock source.

But if the noise is outputting a very filtered signal, so it is more like very low frequency rumbling with no mid or high frequency content, the more likely it will be that the two modules produce the same, or almost the same, stepped output.

This is due to tiny variations in the timing of the sampling in the two modules, and whether the incoming signal tends to have changes that are faster than those tiny differences.
BenJBX
Dave Peck wrote:
Yes, the more high frequency content the noise source has, the more likely it will be that the two S/H modules will produce different stepped levels even when clocked from the same clock source ... This is due to tiny variations in the timing of the sampling in the two modules, and whether the incoming signal tends to have changes that are faster than those tiny differences.


In a nutshell, this is spot on. I also think the implementation of the two s/h circuits would make a difference. Separate modules based on different designs would give the highest divergence. Dual s/h in one module implemented in software on a single processor would probably give the lowest. If you did it in reaktor, you'd most likely find both waveforms were identical.

Typically I haven't got round to trying this yet because I've been on the road with my day job, so thanks to everyone who's given it a go. Most interesting! cool
dooj88
seeing different results is very interesting.. i know weighting higher or lower frequencies is referred to as white, pink, blue, red etc, and i would expect the lower weighted noise sources to potentially produce identical S+H outs as there's less information to be sampled, which we are seeing.

but i wonder about other factors that might play in. are there other way to quantify noise? as in refresh rate, or bit depth, or resolution? what's the sample rate of analog noise, or if that's a gibberish question.. basically i'm asking how densely can data be spat out of a noise source?
pugix
akavalve wrote:
If I trigger 2 (or more) S&H modules from the same trigger source but want them to output different random voltages do I need to use two (or more) noise sources?

I'm assuming yes. Just wondering is there are any other ( i.e. cheaper in terms of $ and hp) options.


Were you not able to try this before asking?
xenosapien
pugix wrote:
akavalve wrote:
If I trigger 2 (or more) S&H modules from the same trigger source but want them to output different random voltages do I need to use two (or more) noise sources?

I'm assuming yes. Just wondering is there are any other ( i.e. cheaper in terms of $ and hp) options.


Were you not able to try this before asking?


Were you not able to tell from his question that he probably does not currently own two separate noise sources?
pugix
xenosapien wrote:
pugix wrote:
akavalve wrote:
If I trigger 2 (or more) S&H modules from the same trigger source but want them to output different random voltages do I need to use two (or more) noise sources?

I'm assuming yes. Just wondering is there are any other ( i.e. cheaper in terms of $ and hp) options.


Were you not able to try this before asking?


Were you not able to tell from his question that he probably does not currently own two separate noise sources?


Thanks for the reprimand.
xenosapien
was it necessary? no.

did I feel douch-y in that moment?... apparently. wink

no offense meant, hope there´s none taken!
pugix
xenosapien wrote:


no offense meant, hope there´s none taken!


I was just embarrassed, because you are right. No offense taken.
Keltie
Ugh. Can we ban the bot? ( assuming no real living person has time for this crap. 50+ spam posts on the same day as registration...)
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