Oscillator drift

[r010159]

Hello all!

The following can happen after a short interval of playing. When I start playing a note, the pitch goes slowly up and down, sometimes as much as an octave. It is not a LFO. Sometimes when I just switch it on, the pitch of the notes are about one octave up from where it should be. Switching the synth off and on sometimes can cure these problems.

So what do you guys think? I am on firmware 1.1.0. Maybe temperature related? The room is at least 90 degrees. Does the synth first need to warm up?

Thanks!

[sdfstudios]

That doesn't seem normal, but nor does 90F seem normal for an interior space.

[r010159]

I do not have air conditioning.

[guyaguy]

I wouldn’t want to even store my synth in a 90F room. But if I did I’d expect odd oscillator behavior. I’m assuming this is just with the VCOs?

[sdfstudios]

I do not have air conditioning.

 Ouch. That's hot. I like to have the windows open, but it has gotten up to 85F in here and then it is time for the AC. Best you can do is hope that it cools down at night, and exhaust all that hot air. Some places that doesn't work.

[r010159]

I wouldn’t want to even store my synth in a 90F room. But if I did I’d expect odd oscillator behavior. I’m assuming this is just with the VCOs?

I do have a small air conditioning unit. Lets see what happens when it has been cooled down. I did reinstall the OS, both components. This has definitely eliminated some of the problems.

Interesting. A cooler room did not help. The DCO seems to be true. The other VCO oscillators are out of tune. I did try calibration and resetting back to factory settings.

I turned it off and on, and this time around, it is playing OK. I did turn it off an on several times, for the same result. What is going on here? I still have some notes not playing when I do a scale.

[r010159]

Here is an update. Each individual VCO sounds fine. When both sound at the same time, there appears to be a slow beating effect indicating at least one oscillator is not tuned correctly. I have not been able to solve this problem even with using the calibration command. All LFOs are disabled. All fine tune knob parameters are in a neutral position.

I am thinking of contacting Sequential for this problem. My seller is trying to help me with this, but nobody there has any expertise with this synth.

Here is an interesting additional problem. It appears I need to recalibrate the oscillators every time I turn the synth on.

Is there some sort of master reset?

[unease]

It appears I need to recalibrate the oscillators every time I turn the synth on.

Is there some sort of master reset?

There should be a way to clear the tuning tables. I know people have had similar problems with the OB-6 and when they cleared the tuning tables and then did the auto tuning a few time, the problem would be gone. I don't think the procedure for this is described in the manual though, so I'd get in contact with Sequential.

[gus]

Hi r010159,

Slight beating/phase differences between the oscillators is normal. You can try setting the 'slop' per oscillator to 0 to see if there is any improvement. I would also recommend re-calibrating the pitch/mod wheels, you can find this option in the Global Menu and in the manual on page 126.

If you continue to have tuning issues, go ahead and reach out to support directly: support@sequential.com

[creativespiral]

As @gus mentioned,  you should always expect some potential phasing/beating with analog oscillators... the small differences in tuning are part of their charm and organic character. 

As a general sound design tip, if you're mixing two or more oscillators at the same octave footing, don't mix them equally.  Try a 70%/30% mix ratio or even 60%/40% or something like that... that way, when they are 180% out of phase (which will occur naturally), the interference won't create an effective "octave up", with more significant beating due to phase interference.   

Or if you have a reason to have multiple oscillators at the same octave footing and same mix level (ie: really punchy bass or other technical sound),  try using osc sync to phase align the initial transient / tuning. 

[r010159]

Thank you all for helping me with my problem.

@creativespiral, I will try your suggestions. I will also look at oscillator slop. A mild beating effect normal for VCAs? This is very interesting!

Does anyone think that using it in a 95 degree room can cause problems?

[creativespiral]

The internal operating temp will normally be way above the air temp in your room anyways (It will probably heat up into the 130-150 degree Fahrenheit range... at least that's how hot my P6 measures once warmed up for an hour), and it should operate fine at 90-95 degrees ambient. 

After the synth has warmed up for 15+ min, just run tuning calibration, and it should stay in tune pretty well...  +/- 3 cents tuning over a four to five octave range is to be expected from VCOs... if the oscillators are off by more than that (and slop / other modulation is off), just try re-running calibration again.   (Note that the init patch on P3 has a small amount of slop applied.. so if you turn that all the way down, you'll see the nominal tuning)

I'm not sure if Pro 3 has similar tuning table index, but this article describes how P6 operates:
https://www.presetpatch.com/articles/Prophet-6-and-OB-6-Tuning-Calibration

[r010159]

@creativespiral:

Thank you for the information that you have given me. I tried everything you have mentioned. I still have the same problem.

Actually, oscillator drift has become worse. I do not know why. Rigjt now, the pitch goes up and down in an irregular fashion. Also, when the sound becomes high enough, there is a high pitch of distortion. It is like using a high amount of resonance on a filter just to the point of self-oscillation.

Interesting.

Bob

[creativespiral]

@creativespiral:

Thank you for the information that you have given me. I tried everything you have mentioned. I still have the same problem.

Actually, oscillator drift has become worse. I do not know why. Rigjt now, the pitch goes up and down in an irregular fashion. Also, when the sound becomes high enough, there is a high pitch of distortion. It is like using a high amount of resonance on a filter just to the point of self-oscillation.

Interesting.

Bob

Hmm.. yeah, that doesn't sound right.   Probably best to record an audio/video example and send to support.  Maybe there's an issue with your unit?   https://www.sequential.com/support/contact-support/

[guyaguy]

Might want to calibrate the mod wheel. It might be engaging LFO to pitch amount.

Otherwise, yeah, contact support.

[r010159]

My retailer gave the videos I made to Seqiential. They said that this oscillator drift is normal. However, these crude “cycles” are becoming deeper. This includes a sine wave at one end of the cycle.

This does not make sense to me. For that matter, how can I design a sound around this?

[guyaguy]

My retailer gave the videos I made to Seqiential. They said that this oscillator drift is normal. However, these crude “cycles” are becoming deeper. This includes a sine wave at one end of the cycle.

This does not make sense to me. For that matter, how can I design a sound around this?

Sequential is probably right but it’s ard for us to know what you’re hearing unless you post audio clips.

[r010159]

Yes, Sequetial is probably right. Good group of professionals.

[Elric]

[Is] A mild beating effect normal for VCAs? This is very interesting!

One thing to look at is the Oscillator Reset in each oscillator. (?)

  *[Osc 3 Shape]*  tab, 3rd dial. - "WAVE RESET"]

This will at least start the oscillators at the same time.
But, when you hold a note "too" long the oscillators WILL drift.
There will be frequency drift across "sequence-time" (longer time periods).

Since the oscillators are analog, they will never completely sync up.
(Even though they are being "tuned" by a digital system.)