Moog Music Forum

I went back and tried this again and got it to work, although it was a lot different than what I expected. Here was my setup:

101-
resonance:10
cutoff:a little above 1k
audio out to 251 s/h "in" (Obviously this could be any sound source)

102-
frequency:a little above 1k
carrier out to 251 mixer 1 in

251-
mixer 1 "in" from 102 carrier out
mixer offset: about +2.5 volts (so sampling happens)
mixer "+ out" to s/h "trig"
(all other mixer knobs at 10)
s/h "out 1" to amp

Then I patched the triangle wave lfo's from the 102 and 251 through the attenuators to control the 102's frequency and 101's cutoff for some variation.

I don't really understand how or why it works, but it does.

where are you patching the sample and hold out to? the cutoff?

nevermind i'm a goof. i just saw it. but i still don't understand how you can control the 102's frequency and 101's cutoff by going into the attenuators. or do you mean the attenuators on the mixer?

what does it sound like?

i wonder if the sampling freq has to be above the freq of what your putting into it for it to work eg:

if you want to hear how it effect a VCO at 200 hz, then you'd need another VCO of at least 200 hz so that it can sample each period of the waveform?

just a thought, as i don't have a CP 251 yet, all i can do is think about it. Can't wait till i get one, i was just about to think about getting round to order one, when the little phatty came out (or until we knew they were up to something, depending on what they would eventually release after all the clues i would get a cp 251 or get the new thing)

by april next year i want my main rig to include
- little phatty (on order)
- midi-cv (probably one of the frostwave ones)
- cp 251
- Mf104sd (already have)

at the moment i don't really have a main rig, just a huge (probably more like.. small but i like to call it huge) pile of keyboards and a four-track MD recorder. sigh, i yern for some CV interaction between my gear

whoops, sorry to drone on.....

Impossible Sound wrote:Right, you won't get into the audio range with just the cp-251 LFO. I used the square out from a VCO as the clock, any audio source (drum machine, whatever) plugged into the input, and the output (you might want to attenuate) to the mixer or amp.

i stand corrected.

yes, the cp251 s/h circuit actually can sample at audio frequencies, its just that the built-in lfo won't go faster than the low audio range on its own. i haven't really experimented with doing things this way much. i recall the last time i tried, of not being able to sample faster than 100hz or so. how fast have others successfully sampled voltages? and have you noticed a difference between how fast the moog circuit can sample compared to other sample and hold modules?

i guess there's only one way to find out.

godzilla wrote:
if you want to hear how it effect a VCO at 200 hz, then you'd need another VCO of at least 200 hz so that it can sample each period of the waveform?

the nyquist frequency ( http://en.wikipedia.org/wiki/Nyquist_frequency ) is the minimum frequency you can sample at to accurately encode the maximum frequency in your signal. (read the link for a more accurate description) in short, the nyquist frequency is twice the frequency you want to sample.

cds are sampled at 44100 hz so they can accurately encode frequencies up to 22050 hz. likewise, if you are sampling at 200 hz, the maximum frequency you'll be able to sample is 100 hz. and you'll hear a lot of artifacts created by all the rough edges in your signal because you're not filtering them out. it's the same phenomena as the aliasing you get when you digitally sample at too low a frequency, and why digital to analog converters have low-pass filters in them.

if you sample a 200hz vco at exactly 200hz, in theory you'll get a straight line (silence) since you'll always be hitting the waveform in the same place. sample a 100hz vco, and you'll get a square wave. sample a 50hz vco and you'll get a very rough "stair step" approximation of the waveform you're sampling.

personally i think sample/hold applications sound a lot more interesting when used to control other modules, and when the control signals are in the sub-audio frequency range, since that way you can really hear the interactions between the sampling waveform and the sampled waveform. but it's a matter of taste.

Duke Foog wrote:nevermind i'm a goof. i just saw it. but i still don't understand how you can control the 102's frequency and 101's cutoff by going into the attenuators. or do you mean the attenuators on the mixer?

Sorry, I should've been clearer about this. In addition to all of the above patching (which would just have the 101 producing the same frequency wave and the s/h circuit sampling at the same speed), I used the lfo's from the 251 and 102 to modulate the cutoff and frequency. Here's the specifics:

102-
patching - "lfo out" to 251's attn 1 "in" - attn 1 "out" to 101 "cutoff"
knobs - rate at .1 and set to triangle wave

251-
patching - "/" out to attn 2 "in" - attn 2 "out" to 102 "frequency"
knobs - rate at .2

godzilla wrote:what does it sound like?

Sampling the cutoff and using the 2 lfo's sounds like a really dirty, edgy version of the 101 with the frequency going up and down in different ways depending on how the 2 lfo's were interacting. higher sampling rate created a clearer sound.

Sampling a guitar sounds like a dirty, messed up version of a guitar. It created a different texture that you may or may not be able to find a use for depending on your tastes.

chris allert wrote:personally i think sample/hold applications sound a lot more interesting when used to control other modules, and when the control signals are in the sub-audio frequency range, since that way you can really hear the interactions between the sampling waveform and the sampled waveform. but it's a matter of taste.

After playing around with sampling the audio a little bit I'm going to agree, but it's always interesting to find out new ways to use things to get different sounds. Stuff like this always teaches me more about the technical end of my equipment so it's good in that way too.