Moog Music Forum

kingfriday wrote:Amos, can you speak to exactly how the LFO modulation is set up on the Sub and how that relates to the external CV modulation bus? What exactly is causing the LFO resolution to be "cut off"?

+1 on this request
I´d like to know if Osc 2 as modulation source is possible from the hardware point of view...if not it will be better to know in order to take the right decision

This times of mod-able and upgreadable synths, even analog ones, feels like a double edged knife since you´re always expected a certain synth to do more, extending the period of knowing the instrument and accept its limitations...

Of course I´m not complaining since there is lot of examples of incredible good upgrades like the arpeggiator in the phatty or midi/cv in the monotribe

I remember the first time I see this kind of extra features added way later of the product release, it was about 1997 with an ensoniq asr-x´s OS upgrade that added pattern change on the fly and then in 1999 access added a vocoder to their virus A synth...this was like "WOW" is this possible???...a vocoder???" at the time it was like sorcery for us

Hey, just got a subphatty, and I'm also very annoyed at the lack of oscillator mod source. Seems so basic I overlooked it when ordering. Why would a Moog leave that out?!?! Seems like something Korg would do, not Moog.

Anyway I'd love to hear if there were plans for an under the hood feature to make this work.

I also was disappointed with the fact that you can't use OSC 2 as mod. source, but that same fact makes me try harder to find workarounds - using fast LFO with tracking, and fast looping envelope. And figuring out workarounds is quite rewarding. Also, SubPhatty's raw sound without any modulation is already giving me goosebumps. Unbelievable bass is coming out this thing, it hits me right in the guts. I've never heard anything remotely similar coming out of my other gear, analog or digital.
All that being said, I wouldn't mind having OSC 2 as mod source, just so i could free up LFO for other stuff.

Would is be possible that the Sub Phatty LFO is not analog (ie digital, and hence a nyquist frequency / bandwidth), since it seems to have a 'resolution' at people are saying here?

To my knowledge, sync'able LFOs are always digital.

I have noticed on some of my patches if i have the mod up and the octave selected as high as it goes, the last (highest) octave will not have any mod on them but if you hit the B...Kaboom. I love this quirk! I don't know if i have a bunch of hidden features on or off, but the patches that do it are some of my favorite. For sure however the keyboard tracking appears to be off. I fear this "feature" may get "corrected" in an update

How about adding the MF-107 FreqBox to your setup?
I'm considering this to expand on the FM sounds on my Slim Phatty, but together with a Sub P it should also be capable of adding some nice FM to that synth.

stiiiiiiive wrote:To my knowledge, sync'able LFOs are always digital.

Do you know at what frequency they are produced?

furiousgreencloud wrote:

stiiiiiiive wrote:To my knowledge, sync'able LFOs are always digital.

Do you know at what frequency they are produced?

What do you mean by "produced"?

stiiiiiiive wrote:

furiousgreencloud wrote:

stiiiiiiive wrote:To my knowledge, sync'able LFOs are always digital.

Do you know at what frequency they are produced?

What do you mean by "produced"?

If the LFO is digital there is a clock, at which the LFO signal is produced, for example at 44.1kHz for audio rates. The frequency of this clock is responsible for the bandwidth limit in digital systems. A clock of 44.1kHz (Let's call this F) can only create waves of 22.05kHz (F/2) or less. This is the Nyquist Theorem. And wave shapes produced these high frequency are very crude, because the system is runs out of resolution at this rate. One can think of this as being able to see the pixels in a visual metaphor, or seeing the jagged edges of a wave form in a audio signal. The production (misrepresentation) of artifacts/jaggies is called aliasing.

Anyway my point is that if the if the clock producing the 1000Hz LFO is only 2KHz the LFO shape will break down and it will sound noisy, and the selected wave shape will not really matter. This would explain what people are hearing on this thread.

Just thought you (or anyone else?! Please!) might know what rate/bandwidth the Digital LFO is running at/being produced at.

If their is no special digital oscillator, this would be the frequency of the microcrontroller that runs in the Sub Phatty divided by the number of clock steps it needs to take to do all it's work. I thought a Moog would at least us Digitally Controlled Oscillator (DCO) for this, which produces a precisely controlled but still analog wave.

So which is it? Is the LFO a VCO, DCO, to Digital-to-Analog Converted Signal?

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.

stiiiiiiive wrote: According to the manual, the LFO has two ranges, allowing it to oscilltate from 0.01Hz to 1kHz.

It has three, actually.

From the Sub Phatty manual, page 28:

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.

furiousgreencloud wrote:Would is be possible that the Sub Phatty LFO is not analog (ie digital, and hence a nyquist frequency / bandwidth), since it seems to have a 'resolution' at people are saying here?

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.

Thanks for sharing that, very interesting indeed