I have a voyager, vx351 and cp 251.
I have had trouble understanding the concept of the sample and hold circuit. 
Can anybody give me an example of a few settings to try so I can hear what’s going on, or ways to make the circuit useful?
Thanks
Chris
The most common use is noise as the input, resulting in a random stepped wave as the output. The manual does a good job of explaining this application.
Alternatively, patch a triangle wave into the input, and the output will be a “staircase” waveform (i.e. a stepped triangle wave)
Use the S+H output on the CP-251 to the filter or wave in on the Voyager with a simple initilized patch.
Experiment and listen to the results.
There are some audio examples of S&H on MoogSpace that illustrate the concepts explained in the manual:
https://www.moogmusic.com/members/?section=files&file_section=3&cat_id=48&file_id=383
Subtle is key here for me…apply a s&h voltage ever so slightly to the pitch of an osc or the filter frequency or resonance, or speed of the lfo for that matter, etc. It can add just a touch of life without resorting to an “obvious” s&h sound.
So to get a snare sound you would use the “Sample” section with a noise source and a short release?
If using the CP-251 there might me a better spread of notes if using the attenuators. Then the 351 has attenuating there too.
concept of the sample and hold circuit
crs.one,
I don’t know if your question has been answered to your satisfaction, as you have not responded (publicly). So I’ll go ahead and add my 2 cents. The output of the S&H is a random stair step pattern. In terms of voltage, an example output string might be, +1.0, +2.4, -3.7, -0.5, +4, +5, +1.1, -3.0… etc. The only thing not random is the rhythm of the output. How long the voltage is held at the output of the S&H is dependent on the LFO speed. (I’ll mention here that you can also make the rhythm random by modulating the LFO speed with the S&H). The S&H circuit generates an output CV by taking periodic snapshots of a white noise wave. A white noise waveform is like the other waveforms (square, sawtooth, triangle, etc.). The wave rises and falls above and below a 0 volt center line. But, unlike those other waves, it is NOT periodic. At any given moment, how high it rises or falls, and the slope of the rise or fall, is random. And any given up/down cycle may or may not cross the 0 volt center line. Thus, at regular intervals, if you take snapshots (samples) of where the wave is, and temporarily hold those voltages in a single buffer, the output of the buffer will be a random stair step. There’s an internal squarewave (under the control of the LFO) which triggers the S&H circuit to take a sample. That’s why the manual says the S&H has 2 inputs (white noise and a square wave). Think of the S&H circuit as a camera. The white noise is the landscape and the squarewave operates the shutter button. Of course in this case, the landscape is a chaotic, ever-changing, collage of light and dark (like what you see on a TV screen when there is no incoming signal). You can send the output of the S&H to a destination to modulate a certain parameter (filter cutoff, vco pitch, etc.).
Heres something that I found on this website.. Its also a great resource for informatoin about modular synthesis
http://arts.ucsc.edu/ems/music/equipment/synthesizers/Synthesizing/usesynth.html
SAMPLE AND HOLD
The sample and hold module was originally developed to be a cheap alternative to a sequencer (all those knobs are expensive). Its basic function is to capture a momentary voltage and keep that voltage at its output until told to sample again. (Keyboards contain this circuit as a matter of course.) If you sample a steady waveform at a slow rate (aliasing) a variety of repeating patterns will emerge that depend on the precise relationship of the two frequencies involved. If you sample noise, you get a totally random output.
Sample and hold with noise input
Most sample and hold devices have a dedicated low frequency pulse oscillator (called a clock) to provide steady triggers.
[Digital systems that claim to have a “Sample and Hold” effect (usually an option for the LFO really produce random steps at a steady rate.]
5.34 THE SAMPLE AND HOLD AT WORK AND AT PLAY
Look back at section 5.2 for a diagram of what a sample and hold does. The output is a step-like control voltage that depends on the nature of the input and the relationship of the input frequency (if any) to the clock rate. Here are the general rules:
If the input is noise, the output is random.
If the input is a waveform with a rate slower than half the clock rate, the output will resemble the input (in steps of course).
If the input is a waveform with a frequency faster than the clock rate, the output will go in patterns that suggest the shape of the input waveform, but may be backwards or scrambled. (It is possible to get an unchanging output this way.)
To find uses for the S&H, we might consider the most common shapes for controls and their uses. Controls may be stepwise and discrete, like the output of the keyboard (portamento off), or sloping, like the output of an ADSR. We usually use discrete voltages for pitches and “preset” kinds of timbre change. Sloping values are good for envelopes and unpitched (or at least untuned) events.
One thing the S&H does is turn a sloping change into a discrete one, so generation of pitches comes quickly to mind.
The easiest thing to do is indeed to generate a set of funny pitches, using the internal clock to provide a steady rhythm. We also want to syncronize the S&H sample with an ADSR to get clean notes. This is done with the clock trigger out. (Synton users can do this by connecting the ext INPUT to the comparator input. The comparator output is a useful trigger.)
There is a small problem with some S&H designs: they let a little bit of the input signal leak through while they are sampling. This causes a glitch as the voltage changes, but the glitch is kept inaudibly short by making the pulse width of the clock very narrow. If you should want to use an external trigger to get a more interesting rhythm (and you should), you must make the pulse you are using very narrow. If the LFO you want to use does not have variable pulse width, make it using the triangle output and a comparator. If you still can’t get rid of the glitch, invert the trigger on the way to the ADSR and turn the sustain off.
Here are some other interesting things to try with the S&H:
Control a filter, sampling noise and triggering with the keyboard.
Control modulation depth (see sec 5.33) of any kind of modulation.
Control pulse width of an oscillator. Use that pulse to trigger an ADSR and the S&H.
Thanks for the article. Looks like a Freqbox might make an interesting S&H trigger.
good call…i hadn’t responded…and i should give my appreciation to everyone who responded.
in truth, i have been doing some renovations at home so my voyager is safely tucked away, and i haven’t had a chance to try any of them yet. but i certainly will.
When you do pull out the Voyager, be sure to delve into the Pedal/Mod Buss Prgm/On source accessed through the menu (Edit, I think). You’ll find one selection not available on the front panel, namely Smoothed Sample and Hold.
Have fun!
Can’t you generate a pseudo-smoothed sample and hold by just bumping up the release time on the envelopes a little?
Eric
Posted: Mon Nov 12, 2007 10:59 pm Post subject: Suggestions for using S&H?
I have a voyager, vx351 and cp 251.
I have had trouble understanding the concept of the sample and hold circuit. Can anybody give me an example of a few settings to try so I can hear what’s going on, or ways to make the circuit useful?
Thanks
Chris
Chris, (from Chris!)
If you want to hear a great example of S&H being used to modulate the filter, listen to ELP’s First Impression. The sound is used to seperate part one and part 2. I just know you’ve heard it… Greg Lake comes in on top of it with the lyric, “Welcome back my friends to the show that never ends…”
Great Sound by Keith Emerson.
Man I don’t know the specifics on how it works, but you can hear an example of how I use it if you go to the link at the bottom of my signature, and listen to the song “The Calm” I did that with the Moog, the Rhodes, and a Synsonics Pro drum machine.
It also can be heard on “Hellicopter”
If you like what you hear, please feel free to add us to your friends list or drop me a line and let me know what you thought about it.
(I normally don’t do shameless plugs, but it is pertinent to the discussion)
hehe
Eric
Chris -
ELP is the best (Emo rules!) and that example you cited is perhaps one of the most well-known S&H sequence ever played, but the song isn’t called First Impression. It’s called Karn Evil 9, and it’s on ELP’s 1973 recording “Brain Salad Surgery”.
There are three movements to Karn Evil 9: 1st Impression, 2nd Impression, 3rd Impression). The 1st Impression was separated into two parts because the entire movement didn’t fit on an album side (we’re talking vinyl here). The 1st impression, Part 1 is the last song on side 1 of the album, and it fades out as Emo’s modular kicks in with the familiar S&H filter modulation. The 1st Impression, Part 2 starts out on the second side with that same filter modulation fading in before Greg intones with the “Welcome back my friends…” lyric.
If you own a CD copy of Brain Salad Surgery (the most recent version was released on Rhino Records), you won’t hear a fade out/fade in between Parts 1 & 2 because they were blended together when the CD was remastered.
A classic example of S&H, though. Good call! 
If you want to hear another great example of Sample & Hold in use, listen to Edgar Winter’s “Frankenstein”. It’s the title track of the album. Near the end of the song (which is instrumental BTW) there is a break where you only hear Winter’s ARP2600 playing a series of descending notes commonly known as staircase modulation:
You connect a low frequency sawtooth in the sample input of the sample & hold and connect the output of said sample & hold to the frequency input of one or more oscillators. You can also use an envelope instead of an LFO and adjust the attack decay and release times accordingly.
You can also hear this effect(faintly) at the beginning of Pink Floyd’s “Wish You Were Here.”
While we’re on the subject of Sample and hold, does anyone know how I can get the keyboard to trigger the S&H ONCE (one single step) with each new keypress? That effect with multipal triggering is an awsome sound and so much fun to play. I just don’t know how to do it on Voyager. Hopefully, I can do it WITHOUT having to buy any extra components.
Chris