Moog Music Forum

On the 921 oscillator, there's a knob marked "Clamping Point." I understand that it has something to do with sync, but I haven't found an explanation of what it does. Perhaps setting a comparator threshold for a kind of soft sync? What are the sonic effects when the signal is below/near/at/above the clamping point?

Thanks for any insight,

THe way I understand it (and I beg for correction because I haven't had time to plug mine in yet) is that as an lfo, the sweep will occur through the entire period. So the clamping point can be moved so the start of the sweep can begin at any point of the period.

I am assuming that the trigger input(s) will start the cycle at whichever point you have the clamp set.

So if you are using a sawtooth modulation, then you can set the clamp point closer to and beyond the peak for varied results.

I could be totally wrong, but I'll know tomorow when I finally get my 921 plugged in and tested.

Videos are forthcoming.

Thanks Eric, looking forward!

Check this...

http://forum.moogmusic.com/viewtopic.php?f=1&t=14525

Thanks, I did see that one, but it still doesn't explain what it does, just how to calibrate and what a 921A/B is for. A demo would be great!

Firstly, the 921A is an 'oscillator driver' - basically an exponential voltage amplifier - it's not an oscillator itself. The 921B is an oscillator but is linear in it's CV/frequency response. So, if you want a 1v/Oct oscillator, you use the 921A to control up to three 921Bs. The 921A also allows voltage control of the pulse width waveform on the 921B.

The combined 921A/921B module is logically enough the 921.

The clamping point is described in the Moog docs as the 'waveform reset control' - i.e. the oscillator waveform can be reset to zero at any point in its cycle. So basically an oscillator sync feature (I think - I have never used it).

I'll have to leave Eric to detail the results, but apparently the 921 doesn't do regular hard (reset) sync, but operates on a phased lock loop (PLL) system. While this can approximate synchronisation (e.g. MF-107 Freqbox) it's more likely to emphasise certain harmonics relative to phase.

If only the patch cables were more clearer..what's going where ?

A 921 is modulating the pitch of a bank of 901abbb oscillators.
A 901 is sending pulse wave outs to the 921 V-Trig input.
The 901bs are going to a C3PO (Moog CP Clone) mixer.
The C3P0 is going to the board. No Filters or VCAs involved.

You're certainly getting some wavefolding going on there! It's still a bit too hard to say exactly what the clamp is doing: is it a phase shift or some sort of voltage threshold (comparator)?

Is the master 901 running at an independent frequency? Or is it one big feedback loop? Might a more straightforward patch just listen to the 921 aux, both separate and combined with the 901? What's the effect of changing the 901 frequency?

Thanks again for your experiments!

I'm sure MC/CZ could answer these questions much better than myself.

The first video used the 921 as an LFO.
We're listening to the 901ABBB bank being modulated by the 921.
The 901, which is running independently, is the source for the wave clamping.

I made this video thinking about the 921 being best suited for LFO duties, with it being triggered with each press of a key. The 901 takes the place of a keyboard.

In the next video which is in the process of being uploaded, the 921 is the audio source.
I conferred with a friend and he told me to take the saw out of the 901, boost it with the C3P0 (Moog CP mixer clone) and use that to the clamp input of the 921.
The result is exactly what was discussed...sync. The confusing part I believe is the terminology. This osc design seems to predate the period before Osc Sync would be popular.
The effect that is has on the waveshape is interesting. Like PWM, you can move the clamp horizontally along the wave.
All of this is evident in the forthcoming video. You will probably know everything you need to know once you see the scope.
I will say that the osc WILL sound better than what I demonstrated on the video but there was a looming thunderstorm.

Eric









Edit: https://www.youtube.com/watch?v=qkXXmXChlVQ

Thanks Eric, this one's much clearer.

Seems like the clamp control acts on the positive slope up to 12 o'clock then starts working on the negative portion?

Cool sounds, enjoy those lovely oscs!

The 921 clamping level is the level to which the oscillators will be clamped on a hard sync via the Clamp Trig input. It is edge triggered with about a 1 mS delay and then the waveform starts from this level. Note all oscillators do not clamp to the same level. I have two scope pictures on my 921 page at http://modularsynthesis.com/moog/921/921.htm

Dave

I hope this response isn't coming in too late. The clamping point feature is an aspect of the 921 Oscillator module that has been begging my interest for some time. But being a new owner of the Moog modular 15, my comprehension of the whole unit has come one step at a time and not without a lot of questions.

Short of my best personal attempt to explain how the clamping point feature works, the best advice I can offer is to download or stream the latest Ask Video on the Moog Model 15 app narrated by Rashabh Rajan chapter 5 (921 Oscillator).

https://www.askvideo.com/course/moog-mo ... ideo-guide

If you own the Model 15... the app version tutorial is a real "door jam" packed full of a lot of insightful tips that apply to both the Moog Model 15 software and hardware versions alike. Check it out, and if that doesn't help just try calling or e-mailing Moog and asking one of the members of the re-edition modular team. They've been really helpful to me so far.

I'd offer my own explanation but I really think the advise I've received in the suggestions offered above, will be more helpful. No sense in reinventing the wheel. I know... the Ask Video download costs $12.50 USD. But let's face it, you own a Moog modular, right? And the app tutorial offers a breakdown of every module.