I’m not sure the Nyquist heorem applies here just as for audio oscilltations; we are talking about control signals.
That being said, a “broken” LFO waveform certainly will result in a broken modulation, and somehow in a weirfer sound. But I think it would not be as obvious as in audio signal.
According to the manual, the LFO has two ranges, allowing it to oscilltate from 0.01Hz to 1kHz.
I got this straightforward: when I read an LFO can go run at XX Hz, I understand it can run there with the specified waveform unaltered.
LFO RANGE SELECTION
The Sub Phatty’s LFO has three selectable ranges: 0.01 to 10Hz, 0.1 to 100Hz, and 1 to 1000 Hz. Although the mixer has no audio input for the LFO, an audio- frequency oscillator can be very useful as a modulation source, allowing the Sub Phatty to produce classic, clangerous FM (frequency modulation) tones.
In Shift mode, press the > BANK 2 > and > PATCH 3 > buttons to change the LFO’s range. Press the low C key to assign the LFO to its lowest frequency range, from 0.01 to 10Hz. Press C# to assign the LFO to its middle range, from 0.1 to 100Hz. Press the D key to assign the LFO to its upper range, from 1 to 1,000Hz.
NOTE: > No matter which range you choose, modulation at normal vibrato rates (between 5 and 10 Hz) is possible.
This had been bothering me, and I persevered with Moog support and finally got this answer - very revealing…
here was my question:
On the SubPhatty,
I was wondering of the LFO was a DCO (Digitally Controlled Oscillator), a VCO (Voltage/Analogue Controlled Oscillator) or a digital level via a DAC (Digital to Analogue Converter) from the microcrontoller.
And if it is the last what is the sample rate/clock at which the DAC is run/the LFO is produced. ie. What is it’s bandwidth limit?
The reason I was asking is that to my hears the LFO starts to break down at high frequencies and get really “chunky”. I’ve also heard other reports on the forums to this effect especially when combined with LFO Keyboard Tracking to increase the frequency. Also since the SUB37 is said to have the same voice structure, it would seem to me that the LFO is based on a DAC because the SUB37 has two bipolar Mod. busses which would be most easily implemented in firmware on the microcrontroller. ie, If the Sub37 was a SubPhatty with more knobs, but the same “engine”…
/quote]
And the answer.
Yes the oscillators are free running analog, but the CV that determines their pitch is DAC based. The LFO is the same, and has a musically pleasing response for FM up to about 500Hz. It will produce useful waveforms up to 1000Hz however there will be some distortion resulting in the type of response you referred to on the Sub Phatty. This response is also contingent on how much other stuff you have going on that can tax the processor lowering the overall musical sweet spot of the LFO for FM work.
I hope this answer was helpful.
Thanks,
ANDY HUGHES
SERVICE DEPARTMENT MANAGER
MOOG MUSIC INC.
