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[easy_lee]

I'd be grateful if somebody could help me understand a few things about the S&H module on the MS20 (Kit):

a) What audio signals can I use as trigger (clock) input?

I've tried using a very short percussive sound which I placed at every 16th (or 8th) of a beat in my sequencer. This works for a few seconds but then the triggering stops and I just hear the white noise I fed into the S&H input mixed in with the actual audio signal of the MS20.

b) Using the KB Trig Out as clock and white noise as input signal, I can hear white noise whenever I release a key. Why is that?

I have the S&H Out patched into Total. The filter is modulated by EG2 and T. Ext. The noise is most obvious when I increase the release time on EG2. As long as I hold down a key there is a normal sound. As soon as I release it, the only thing I hear is noise.

I thought the way this was supposed to work was that with every gate signal the S&H module would sample the voltage of the white noise. The voltage output of the module would then stay on until the clock input receives another gate signal. But it seems that when the gate voltage resets from 5V to 0V this also has an (unpleasant) effect. Why?

[OpAmp]

Hi

a) You can use whatever signal, but it goes best with a clock signal, like the one output by the modulation generator on the MS20, with the waveform knob turned completely clockwise. This gives a waveform that looks like a small pulse.

Some more info on S&H: it is more a track and hold. It means, when the clock signal is high (x Volt) it passes the input signal to the output. Only at the moment the control voltage drops to 0 volt, it holds the last input level and keeps that at the output.
That explains why the thin pulse of the waveform generator resembles the most to sample and hold.

b) Some more info on the keyboard trigger signal: if no key is pressed, the trigger signal is high. At the moment a key is pressed, the trigger signal is 0 Volt.

So if you combine this info with the one on S&H, the story is like this for the keybourd trigger as control signal for S&H: If you don't hit a key, the trigger signal is high and the S&H function just passes the noise signal from in to out. At the moment you hit a key, the input value is hold and put on the output signal. This explains why you hear a normal sound (though it should be different each time you re-hit the same key) when holding a key. At the moment you release the key, the noise input passes to the output of S&H and starts to modulate your sound, which is then going through its release part of the EG. So the noise effect becomes more significant when increasing the release time of the EG.

Try to decrease the release and hold time of EG2 to reduce the effect, or use another control signal.

Have fun.
_________________
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Alesis SR18, Akai Miniak, Fender Strat, Line 6 Spider II 112, Zoom MS-50G

[easy_lee]

Thank you very much indeed! I wasn't aware of the difference between Sample&Hold vs Track&Hold. This explains everything.

Well...almost. Just one more thing: Why do I hear noise if I modulate the synth's filter with white noise (connecting the white noise output to the Total input)? I would have expected to hear a random change in cutoff frequency. Especially if I set the T.Ext knob to just 1 or so.

[OpAmp]

Hi,

Well, I can not try this at home (no MS20)

But I can think of some reason...
It will sound noisy, but not as in white noise. The random noise will continuously jump in all directection causing the filter to open and close randomly.
The waveforms of the oscillator contain quite some harmonics, which will be selectively passed or suppressed by the modulated filter and this at a very high rate, causing a noisy sound.

It should be least outspoken using the triangle wave (because higher harmonics have less amplitude). Due to that the filter will act like amplitude modulation and may give some stuttering tone.

Bye.
_________________
microKORGXL, Kaossilator Pro, monotribe, SQ-1, volca fm, Kross 88 BK
Alesis SR18, Akai Miniak, Fender Strat, Line 6 Spider II 112, Zoom MS-50G

[easy_lee]

Sounds plausible. Thanks.

I am still wondering why I don't get the MS20's S&H to clock to an audio click. I've tried all sorts of ultra-short signals. It's always the same: once I plug in the cable, clocking works for a few seconds but then it stops working. Does anyone have experience with that?

[OpAmp]

Hello,

Mmh, I think that a real audio signal is not the best you can choose as clock input. Even though you make it short, it will still be an audio signal probably. Meaning you get several amplitude swings, while you probably want one. The hold functionality is based on a capacitor. So my bet is that you get some saturation when using an audio signal, i.e. the cap is full. (Don't take me wrong if this explanation is not correct.)

I was thinking if you could use the external audio processor to route your audio signal through and use the trigger out signal from that, which is more clock like. But I'm afraid, it has the same issue as the trigger generated by the keyboard: being high between your beats and putting the sample and hold in pass through mode...

Bye
_________________
microKORGXL, Kaossilator Pro, monotribe, SQ-1, volca fm, Kross 88 BK
Alesis SR18, Akai Miniak, Fender Strat, Line 6 Spider II 112, Zoom MS-50G

[easy_lee]

I was thinking the reason could be that an audio signal has positive and negative voltages and the trigger signal should have only a short positive one. I'll see if I'll be able to find an appropriate signal.