Can't reduce higher harmonics

Can't reduce higher harmonics
« on: October 21, 2023, 06:35:53 AM »
I'm trying to get a clean pluck sound from my Rev 2 and have an odd, higher harmonic sound that is always present.  It's apparent with an init patch and applying some filter and amp envelope to get the pluck.

I'm attaching a recording that shows what I'm hearing.  The first three chords have the amp env release at about 1200.  Then the next three chords have max amp env release so you can hear the sound more clearly.  It rings out after the filter env decay.  Even with the release down at 1200 you can hear it on top of the notes in the chords, so it seems to be coming in somewhere ahead of the amp envelope.

I've never noticed this before - how do I get rid of it?  Or is it some kind of defect?

« Last Edit: October 21, 2023, 06:37:29 AM by rgames »

Re: Can't reduce higher harmonics
« Reply #1 on: October 21, 2023, 07:20:42 PM »
Sounds like what the filter is letting thru after it has closed...
Minimoog D (vintage), OB6 (Desktop), Oberheim Matrix-6 (MIDI Controller), Prophet REV2-16, DeepMind 12, VC340

Re: Can't reduce higher harmonics
« Reply #2 on: October 21, 2023, 10:48:54 PM »
I had something similar with a preset and some strange noise when gated sequencer wrapped around.
- slew did not work quite right

Try make a calibration of filters and oscillators.
- it did the trick for me

First calibration hung, but then doing a global reset and calibrate again it all went fine.

Re: Can't reduce higher harmonics
« Reply #3 on: October 22, 2023, 09:35:17 AM »
Yeah I did the calibration and resets and everything I could find related to resetting to factory defaults and the noise is still there.

I think it must be a defect of some kind.  I've had it for a few years and don't recall hearing anything like that before.  I just pulled it back out after not using it for a while.

Here's another example alternating between the Rev 2 and a Matriarch.  The Rev 2 clearly has a bunch of higher harmonics the linger after the decay.  I can't get rid of them, even with the filter all the way down.

Re: Can't reduce higher harmonics
« Reply #4 on: October 22, 2023, 10:43:44 PM »
The second sample gives the vibe of ground loops creating digital noise.

If any usb for midi I would disconnect and do phones out and see what gives.
- if that helps use din midi instead

Usb will give ground through usb and then ground over audio cables  too.
- din midi is separated with opto couplers and remove that usb ground

Re: Can't reduce higher harmonics
« Reply #5 on: October 23, 2023, 09:11:44 AM »
Yeah agree it has a ground loop kind of sound.  I disconnected the USB and the noise is still there.  Also, the Matriarch is right next to it connected to the same power and audio interface.

I tried the headphone out but I could barely hear anything.  I don't think that output is working correctly - it might be related to the noise I'm hearing.


Re: Can't reduce higher harmonics
« Reply #6 on: October 23, 2023, 08:21:51 PM »
I would continue disconnecting also line out on REV2 and listen to phones out.
- so all isolated

If Matriarch is using usb midi that still is a ground loop in the total circuit.
- so shortly disconnect that midi first maybe and listen to REV2

This is the nature of ground loops, very hard to explain why REV2 is affected and not Matriarch.

Re: Can't reduce higher harmonics
« Reply #7 on: November 19, 2023, 09:32:31 AM »
Friendly bump - can anyone confirm that this is *not* normal for the amount of noise getting through the filter on an init patch?  I've made another recording where I do a filter sweep on the init patch, starting about half open and going to fully closed then repeating a few times.  It's  uploaded here:

Also, it sounds the same through the headphone outputs and connected to different power circuits, so I don't think it's a ground loop.  I sent it off to Sequential and they say it's fixed - the recording above is the synth after I got it back and it sounds the same (to me) as before I sent it off.  I don't recall hearing this much noise coming through the filter over the several years I've owned it.

Any confirmation or related experience would be greatly appreciated so I can figure out whether I have to send it back yet again.  It would be great if someone could record their Rev 2 doing a filter sweep on an init patch so I can compare.