Need help with testing something...

[Razmo]

Hi everyone... I have a small favor to ask of you... I've attached a .syx file for you to test this with... it loads into the edit buffer, so no worries about it overwriting anything in your REV2.

I need someone to test this, so I know if this is only my REV2 sporting this "feature", or if it's just the way the REV2 works.

The test program is a simple program that use the filters in self oscillating mode, with oscillator 1 set to a triangle, and oscillator 2 set to "off"... the oscillator mix is set to only play oscillator 2, or in other words; the oscillators are NOT sounding, only the filter.

The reason for oscillator 1 set to triangle and not heard is, that I want this oscillator to audio modulate the filter via the parameter "Audio Mod" for some FM action.

Problem is, that as i turn up the audio mod parameter, I get differences in the pitch between the voices, and the shift seems to come in fours... that is, first four keypresses are in tune, but then the next four is a bit different, but enough to make it impossible to use the sound for playing anything melodious...

I'm suspecting that it may be the 8-voice add-on board I got in my REV2 that somehow tunes it's filters a little bit off in regard to the onboard 8 voices...

I'd like to be able to use the Audio Mod with a static high setting, but this is just not possible because of this... I wonder if this happens with your REV2 8 or 16 voice as well?

I've attached a small demo showing what it sounds like: http://razmo.ziphoid.com/TestProgram.mp3

The demo first play the self oscillating filter without any Audio Mod, then with...

[Razmo]

I may add that i do not believe it to be the filters tuning a bit off like I wrote above, simply because when the Audio Mod is turned all the way down, the filters are playing perfectly in tune over all keys and all voices... so it cannot be the filters... after thinking about it, it must be the Audio Mod (which is in essence an "amount" parameter) that is off a bit on the add-on voice board or the A/B wiring... it's common knowledge that the more you add FM modulation, the more the sound gets out of tune, so that would make good sense as to why this is happening if somehow the amount differ a bit between the voices... the funny thing is though, that if in stacked mode, which should ideally separate the two 8-voice boards, then it's still 4 in tune, then 4 a bit off and so on... maybe each board is split into two because of the A/B design... have to be since A/B layers are also present in an 8voice REV2... this would also explain why it does the same in stacked mode... maybe with an 8-voice REV2 you get the change every two notes?

I know, that by judging from the demo I attached, it can sound like very little differene... but trust me... as soon as you start playing melodically, it starts to sound pretty false, and it gets worse the higher the Audio Mod setting is.

[AlainHubert]

Hello Razmo.

Downloaded your sysex file, and on my 16 voice REV2, and I get even worse results than you. If I play low notes, they are all pretty much in tune, but when playing higher ones, the pitch is all over the place, but repeatable when exceeding 16 voices.

I think it has to do with the very slight inconsistencies of the filter tuning at higher frequencies. Here's a short audio file of me playing all C notes, starting with the lowest, on the keyboard 16 times each.

http://www.mediafire.com/file/4g70x0yivx6h67d/REV2_FM.wav/file

BTW, I've noticed in your audio sample that 4 of the voices on your REV2 are panned slightly to the right compared to the other ones, although I don't have this behavior on mine. I'm still on firmware 1.1.4.5 though.

[Razmo]

Please try and set Audio Mod all the way down and listen again... In this case you should have the filter playing and it should be in tune and sound fairly consistent on all keys... If you have tuning problems in this case between the voices, you need to calibrate your REV2 because that is not normal... Just remember to let the REV2 warm up before you do it for about half an hour, then shut off the synth for ten full seconds and then back on before doing the calibration (otherwise it may freeze during calibration)... After that you SHOULD have a perfectly sounding tuned filter... After this, please try and crank up the Audio Mod again and listen for differences

[AlainHubert]

Sorry for the delayed response, been busy.

I did what you suggested and the filter on each voice is pretty much in tune with all the others. The result is identical from the sample I posted before, with the same inconsistencies between voices when Audio Mod is raised. But, all things considered, I think it's as good a filter tuning as with any other synth with analog filters that can self-oscillate and that can track the keyboard 100%. Because if I hold notes and play all C chords across the whole keyboard, the result is very much in tune, without any Audio Mod applied.

Audio Mod is FM, and with FM it's extremely difficult to get accurate and precise results with analog sources. That's why the Yamaha DX7 is all digital by design. You might say that the REV2 is also digital, with the way the Oscillators are digitally controlled, but the self-oscillating filters are analog and imprecise even when controlled by a digitally generated analog Control Voltage. That's the fly in the ointment of trying to get a precise pitch out of frequency modulating the filters.

Here's the filters (all 16 voices on each octaves) on my REV2 self-oscillating away without any Audio Mod applied.

http://www.mediafire.com/file/bh13cl0v1kmmsab/REV2_Filter_play.wav/file 

[Razmo]

Sorry for the delayed response, been busy.

I did what you suggested and the filter on each voice is pretty much in tune with all the others. The result is identical from the sample I posted before, with the same inconsistencies between voices when Audio Mod is raised. But, all things considered, I think it's as good a filter tuning as with any other synth with analog filters that can self-oscillate and that can track the keyboard 100%. Because if I hold notes and play all C chords across the whole keyboard, the result is very much in tune, without any Audio Mod applied.

Audio Mod is FM, and with FM it's extremely difficult to get accurate and precise results with analog sources. That's why the Yamaha DX7 is all digital by design. You might say that the REV2 is also digital, with the way the Oscillators are digitally controlled, but the self-oscillating filters are analog and imprecise even when controlled by a digitally generated analog Control Voltage. That's the fly in the ointment of trying to get a precise pitch out of frequency modulating the filters.

Here's the filters (all 16 voices on each octaves) on my REV2 self-oscillating away without any Audio Mod applied.

http://www.mediafire.com/file/bh13cl0v1kmmsab/REV2_Filter_play.wav/file

I agree... I just wanted to make sure that I wa not the only one experiencing this... I know that FM is hard with analog curcuits because the oscillators need to be extremely stable, so i actually expected some difference... what made me wonder was that in my case it seemed to go in "pairs of four"... anyway, I'll just refrain from using FM for getting any steady playable sounds because it does not sound very good with Audio Mod turned up... it's good enough for creating transients with an assigned envelope generator though... in that case, the small difference actually make the transients sound a bit more organic...

Thank you for testing this for me... appreciated!

[AlainHubert]

You're welcome.

[Trackdriver]

I didn't download the patch but created one myself with the same settings as described in the first post. I have only owned the Prophet Rev 2 Desktop for a couple of weeks and have only began learning it. I have tried making FM sounds a few times but have always failed because I couldn't get the filter in tune. Every time I hit the same key I got a different note. When I saw your post today I thought I would give it a last chance. That was when I saw the "Key Amount" knob in the filter section for the first time! I have previously used the mod section with "Note Number" as source and "Cutoff" as destination instead of just turning up the key amount knob. This works so much better.

Anyway, I have uploaded a file here:
http://tiltshiftgallery.se/audio/ProphetRev2_Filter%20FM.mp3

It's devided in two parts - one with eight repeated notes and one with a short melody. I have moved both parts up one octave after each session and switched between "Audio Mod" on and off. The results are varying depending on where on the keyboard you play, tuning of the oscillator etc.