Issues in Unison Mode

[-AJ-]

Hey -

I was wondering if anyone else has noticed issues in unison mode, where the low frequencies come and go. When I look at it through a metered input, the signal is rising and falling by as much as +/-10dB, and the rising and falling of the sound is in the low/sub frequencies.

Trying to figure out if it's a defect in my unit, or if it's a design issue common to all of them.

[IAA Music]

Are you sure it's not PWM modulation or even waveform phasing?

Does it happen in a clean patch with unison on and no slop or modulation?

Ian

[-AJ-]

I've tried every setting I could to isolate it. Effects off, LFO and Poly Mod settings at zero, filters set wide open, slop at zero. It only happens in unison. It happens with each oscillator individually, on any waveform, and in combination. It happens with any key mode setting, and any number of voices 2 or greater in unison. It doesn't happen in unison set to 1 voice. It's only noticeable with low frequencies, when either oscillator is tuned low, or with the sub oscillator. It's a slow cycle, that takes time to go from minimum to maximum volume for the low frequencies. The higher frequencies don't seem to be affected.

I first noticed it when playing a bass patch in unison, where the low frequencies seemed to disappear and then reappear. It happens whether I play short notes or hold one note for a long time.

It seems like the most likely explanation is a very slight variation in tuning or phase between the voices when more than one plays the same note. It sounds like the notes slowly going in and out of tune or phase, with the low frequencies canceling each other out, then combining to become loud, and back again. This is the first fully analog synth I've owned, so I don't know if it's standard behavior, or if it's unique to the Prophet-6, or unique to my individual unit.

It is a significant problem when trying to play a bass sound in unison. Having the low frequencies completely disappear is not good. I've tried auto-calibration already while I was trying to isolate the problem, but maybe doing it more will improve it.

[robleighton22]

this has thrown me off as well. i think its because the wave forums are constantly moving and not in sync. so you are layering 6 voices of at least 1 oscilator on top. so lots of movement happening and that might cause the phasing. i was getting an odd situation where unison on oscilator 1 was reactiing different to unison on oscilator 2. but strangely that has seemed to disappear.

[keencurl]

Same thing, with my P6...Is it normal? OSC slighty drift, and volume up and down a bit, in UNISON mode?

[IAA Music]

Most likely- in unison mode try turning slip up and down to see if detune between voices is what you’re hearing.
That variation is what it’s all about. Mind you it’s also why digital synths were once lauded as so cool and clinical!

[cbmd]

The oscillators in the P6 are free running.  As such, when in Unison mode, you will hear phasing due to phase cancellation.

[nunnun]

Is there any way around this though? Great that they're free running but it's impossible to stabilize bass patches in unison this way.

[osflaa]

Is there any way around this though? Great that they're free running but it's impossible to stabilize bass patches in unison this way.

As far as I know, out-of-phase oscillators are the reason why unison produces a fat and wide sound. If the oscillators were in perfect sync, unison would do nothing more than increase the volume.

[Manbird]

Is there any way around this though? Great that they're free running but it's impossible to stabilize bass patches in unison this way.

Try using only one oscillator, or try syncing the two oscs. I've been getting some very satisfying P6 unison bass tones this way. Solid and with presence, but clear and holding tight in a mix...

[MPM]

I’m with Ant on this one.
Use OSC sync.
Personally, I prefer to use 1 voice unison anyway. By using OSC sync, you can add a touch of slop, and you get a much more organic bass that always starts at the same point in the wave.
If you need extra grunt, use gain in your mixer, or a teensy bit of the P6’s Distortion.