ACE - unipolar LFO modulation

[bg]

I figured out how to get unipolar LFO modulation using ACE’s Mult. (I realize it can be done more simply with the mapper, but I want to understand the Mults and Amplitude Modulation.) Anyway, with this patch unipolar LFO modulation works perfectly, but I don’t understand why it works. Specifically, why is the LFO’s negative excursion eliminated?

From the manual, Amplitude Modulation in ACE is expressed as
Y = a*(1 - mod)
Substituting the signals in the screenshot the expression would be:
Mult Output = ModWheel * (1 – LFO)
Correct?
Also, I did read this thread:
http://www.kvraudio.com/forum/viewtopic ... 1&t=404338

[Howard]

"Correct?"
I think so! (I can't experiment right now)

"why is the LFO’s negative excursion eliminated?"

ModWheel * (1 – LFO)
The LFO value limits are -1 and +1. You would never get a negative result from that formula.

[bg]

ModWheel * (1 – LFO)
The LFO value limits are -1 and +1. You would never get a negative result from that formula.

Ok, I see. Thank you!

[Howard]

Ah, it doesn't work - some of the mod wheel signal gets added. Difficult...

The following works, but uses up LFO2 amp mod socket. Can anyone improve?

[justin3am]

Why not mix the +5 output (offset) with the LFO signal. Send the LFO to Mixer input 1 and +5 to mixer input 3. With the LFO level set to 100 and the gains on the mixer both set to 50, an LFO which normally swings between -1 and 1 with the center at 0, will now go from 0 to 1 with the center at 0.5.

[justin3am]

Also, if you patch LFO output to both input 1 on the mixer and the mod input, I think you will get a full-wave rectified version of the LFO.
....or something like that. In any case the output seems to be unipolar and twice the rate/half the amplitude of the signal going in.

[Howard]

Yep, that works justin3am

[bg]

Ah, it doesn't work - some of the mod wheel signal gets added. Difficult...

The following works, but uses up LFO2 amp mod socket. Can anyone improve?

“..it doesn’t work..”

Sorry, but I don’t understand what you mean. Here’s audio using the patch I originally posted. Increasing MW makes the pitch modulation go up while the mean pitch doesn’t change.
ACE Unipolar LFO mod

I tried the patch you posted—and I probably missed something—but the result was LFO pitch modulation that went BELOW the mean pitch as MW increased. This works, but is the opposite of what I intended. But more importantly, your patch changes the basic tuning of the Osc, because of the VCO Frequency Modulation Range setting.

Again using your patch, I discovered that simply routing +5V to mixer input 2 (instead of 3 or 4) fixes the tuning issue, and makes it behave exactly the same as the patch that I posted, though requiring one extra cable.
Thanks for spending time on this. I appreciate the help.