Sub 37 Audio Rate LFOs

[rosschehayeb]

I'm strongly considering buying a Sub 37, but I have a question about the LFOs. I understand that when switched to high range, the LFOs go up to 1000hz, which is somewhere around A6 I think. This is very fast. When the LFOs are going this fast and they are routed to modulate the oscillators, would this be considered FM modulation? Does it sound like what a cross modulation of oscillators usually sounds like? And if routes to the filter, does it sound like typical filter FM?

I'm just trying to figure out if the fact that the audio rate modulation is coming from LFOs makes it different than audio rate modulation coming from an oscillator.

If anyone could post sound clips of the LFOs doing audio rate mods of the oscillators and filters, that would be great as well.

Thanks,
Ross

[mmarsh100]

Too many zeros. From the manual:

LFO RATE
By default, the LFO RATE knob varies the low-frequency oscillator’s modulation rate from 0.1Hz (one cycle
every 10 seconds) to 100Hz (100 cycles per second). This can be multiplied 10x by using the HI RANGE button.

10 x 100 = 1,000 not 10,000.

But, that said, you can do FM-like sounds by modulating an oscillator (or the filter or both) with a fast LFO on the Sub 37. It's just limited by the relatively slow audio rate possible on the LFO.

[rosschehayeb]

I said 1,000 hz, not 10,000. But thanks for your reply. But I'd like to push back a bit on something you said. You say the LFOs are slower than the oscillators, but the LFOs go up to 1000 hz, which is about A6. This is higher in frequency than you would usually have your oscillators, unless you set them at 2 or 4 feet, which is not usual. So it seems the the LFOs can go at least as fast as the oscillators if not faster for what your oscillators would normally be at. So does this mean that oscillator and filter FM via the hi range LFOs sounds like genuine oscillator and filter FM? Or does some other reason I'm not thinking of change the way they act as audio rate modulators?

Ross

[fwilleke]

It does work, you can get FM-like tones from it.
However, to get real musically usable FM sounds, you would need some more control and more stable oscillators (not analog then).

Also, the LFOs are digital, as far as I remember. So you're kinda limited in, let's say, how detailled they affect the sound. No idea how to say it.

I remember Amos(?) saying somewhere that the core CPU frequency of the Sub 37 could be increased, possibly resulting in better sounding LFO FM. I'm not aware this step has been done yet.

[mikeh11]

So does this mean that oscillator and filter FM via the hi range LFOs sounds like genuine oscillator and filter FM?

Yes. In my experience, though, keyboard tracking was a little touchy. With KB tracking at 100%, it felt like the "slope" was off a little. By that I mean: tune the LFO so the beat frequency pattern is what you want, and then an octave or two away, the beats would be faster. So, it's a good analog simulation! As ' fwilleke' said, you'd want amplitude control over the modulator... I guess the other LFO could do that...

[DeckardTrinity]

That's been my experience as well - I like to call it pseudo-FM. You can get FM-like tones out of this technique on the Sub 37, but this is one of those things where I think a synth like the Voyager really shines (when folks are asking why stick with Voyager or downgrade to 37, this is the reason why to have both!)

The LFOs in the Sub 37 also like to "step" at certain times... I don't know if this happens all the way across the frequency spectrum, but when I'm trying to dial in the exact FM-like modulation that I want, I find that it's almost impossible to get it perfect due to the aliasing.

[rosschehayeb]

Thanks guys that answers my question. I think the "pseudo-FM" will be enough for me, as one of my favorite things to do is run an LFO at an audio rate and barely fade it in to emphasize different harmonics. Seems like the LFOs can do that.

Now I've just got to find someone that wants to trade their sub 37 for my Prophet 08 PE Desktop with the upgraded P6 knobs. If you know anyone who would like that, hit me up.

[rosschehayeb]

I was just reading the manual and it states that 2 of the programmable modulation sources on the instrument are:

OSC1 PCH: Oscillator 1’s Pitch
and
OSC2 PCH: Oscillator 2’s Pitch

Is this different than using the oscillators as audio rate modulators? Can someone explain to me what this means?

Thanks,
Ross

[robbd]

Yeah, that's a little misleading.
What the manual means is:

"OSC1 PCH: Oscillator 1’s *Octave Selector Switch*
and
OSC2 PCH: Oscillator 2’s *Octave Selector Switch*

i.e. the Mod Source is the the position of the switch - eg. 16' - not the frequency of the oscillator

[rosschehayeb]

Oh I see. Yeah that's a little misleading. Thanks for clearing that up.

[robbd]

In the interest of total clarity, the above applies to cross-modding the oscillators, which I believe is impossible on this synth.

Audio rate modulation of other parameters MAY be possible, I don't have the synth here to check.

[rosschehayeb]

In the interest of total clarity, the above applies to cross-modding the oscillators, which I believe is impossible on this synth.

Audio rate modulation of other parameters MAY be possible, I don't have the synth here to check.

Really? Can anybody who has the synth confirm this? It seems like this would be a big selling point if it were so.

[robbd]

I HAVE the synth, it lives in my studio.

CONFIRMED-
Using the oscillators to mod anything is impossible, that page in the "CONTROLLERS" menu refers to the physical controllers only.

eg. assign OSC2 PCH to cutoff will let you control the filter with the Osc. 2's Octave Switch and Frequency knob

eg. assign OSC2 PCH to ARP Range and Osc. 2's Octave Switch and Frequency knob will change the range of the Arpeggiator, etc., etc.

So in short, cross mod IS impossible, modulation of ANYTHING by audio is impossible.

The HI RANGE setting on the LFO's or looping an EG will almost get you there, but if you need a SW radio / hound dog howling into a feedback loop kind of sound, it ain't going to happen.

[rosschehayeb]

Thanks for clearing that up. For those of your that have tried to tune the LFOs at an audio rate and found it to be off, have you tried setting the programmable source to a sine wave? I wonder if it might respond a little better that way.