Unable to get perfect square wave ACROSS ENTIRE KEYBOARD

[awelchel]

Has anyone else had trouble getting a perfectly hollow (50%) square wave across the entire keyboard?  52% pulse wave is fine for most notes, but some notes are buzzy and shape needs to be set at 53% to be "clean and hollow".  Tried recalibrating oscillators & filters, but the problem persists.

[AlainHubert]

Has anyone else had trouble getting a perfectly hollow (50%) square wave across the entire keyboard?  52% pulse wave is fine for most notes, but some notes are buzzy and shape needs to be set at 53% to be "clean and hollow".  Tried recalibrating oscillators & filters, but the problem persists.

Make sure you have the latest firmware revision (currently 1.1.3) and have done a calibration more than once.

But, having done so on my rev2, it's the same result as on yours: 52% is good for most of the voices for OSC 1, but for 3 of the 16 voices I have to set 51% to get a hollow square wave. For OSC 2 I have to set Shape Mod to 51% to get most voices hollow square. And even then, on 4 of the voices I have to set it to 52% in this case to get a square.

It's even more evident when viewed on an oscilloscope, with duty cycle varying up to 0.8 %from voice to voice for both OSC 1 and OSC 2 when Pulse is selected and Shape Mod is set to 52 %.

Looks like a calibration inaccuracy.

[extempo]

Keep in mind that this is a synthesizer and not a piece of test equipment. There will always be some slight variations. From voice to voice, and even between both oscillators in a single voice.

[guyaguy]

Does engaging NOTE RESET help get what you're after?

Keep in mine that this is a synthesizer and not a piece of test equipment. There will always be some slight variations. From voice to voice, and even between both oscillators in a single voice.

It's funny how there's one group who cries out "It's not perfect enough!" and another "It's too perfect!" There's probably not a single analog synth out there with perfectly consistent oscillators.

[AlainHubert]

If there is one thing that a mainly digital synth (albeit through a DAC control voltage), with DCO oscillators, should be good at would be to produce a pulse wave of consistent duty cycle, no ? I’m just saying...

[vincent neutron]

Dco’s are too analog now!🤔

[guyaguy]

If there is one thing that a mainly digital synth (albeit through a DAC control voltage), with DCO oscillators, should be good at would be to produce a pulse wave of consistent duty cycle, no ? I’m just saying...

Hm, I'm not sure that's something that is related to DCOs. I'm not a synth designer or an EE but from what I understand the digital control on a DCO is the wave cycle of the oscillator, not its shape.

Just out of curiosity I tested my Rev2, and I couldn't get a square wave across the keyboard. In fact I couldn't get a pure square wave anywhere at all. There's always a bit of buzz to the sound, which is not atypical really. Is it possibly because they are sawtooth-based oscillators?

Then I tested my Subsequent 37's VCO square, and it's a bit buzzy as well. In fact, both behave in the same way, which is that the top of the wave you'd expect to be flat slopes left to right on lower octaves and right to left on higher octaves. The attached pics are of the Moog but the Rev 2 behaves similarly.

All of which is to say I don't see it as an issue as such.

[Sacred Synthesis]

I haven't seen the Prophet '08's square wave on an oscilloscope, but I presume it's imperfect on that level.  But I can tune the pulse width to a point (48) at which me ears hear a perfect square character for the length of the keyboard, with no even partials.  If I move the width to 49 or 47, I can already hear the loss of purity as other partial appear.  So, I'm completely satisfied with the P'08's square and I haven't had a problem like some folks have reported with the Rev2.

[jdt9517]

Analog oscs will be imperfect.  The digital oscs of the P-12 and Pro-2 create pretty much "perfect" square waves.  This is why it sounds too sterile to some people.  Analog=imperfection.

[extempo]

If there is one thing that a mainly digital synth (albeit through a DAC control voltage), with DCO oscillators, should be good at would be to produce a pulse wave of consistent duty cycle, no ? I’m just saying...

The digital portion of the DCOs in the Rev2 is strictly the reference for pitch. The electronics that generate the waveforms are completely analog. There are component tolerances, etc., and they won't be perfectly symmetrical from voice to voice, or even between the two oscillators within a voice. They'll be pretty damn close though in most circumstances. It's misleading to say that the Prophet Rev2 is a mostly digital synth. The signal path is completely analog save for the digital FX engine.

I'm stating this for the purposes of clarity for the average reader--I believe you know this already.

[AlainHubert]

I wrote « mostly digital » because every control in a REV2 is being calculated by a CPU/DSP (envelopes, LFOs, waveform shape, modulation sources and destinations) and then being converted into an analog control voltage by a DAC and then sent to the Curtis, sorry, DSI music chips. The sound itself might be analog, but the control is purely digital.

[extempo]

Yes of course, but what I’m saying is that the precision of the control voltages is not directly correlated to perfectly symmetrical waveforms. You can have identical CVs applied to two of our Curtis DCOs and you won’t get absolutely symmetrical waveforms due do component tolerances. 

[AlainHubert]

I agree that component tolerances is a factor.

Imprecision is to be expected on a 33 years old Oberheim Matrix-6 (which uses 6 Curtis 3396 chips almost identical as the ones in the REV2), because of the limited digital technology of the day (slower processors, limited resolution ADC/DAC, limited amount of memory that was expensive then). But on a ultra-modern synth, with today's extremely powerful processors, inexpensive memory, and high resolution converters, I would have expected at least 255 values for all the potentiometers/parameters, and a calibration routine capable of enough resolution to cancel out any unwanted component tolerances variations from voice to voice on critical parameters such as wave shape/waveform duty cycle. When I dial-in 50% pulse width in order to get a square wave, I don't want 52% or 48% on some of the voices.

Would anyone settle for an imprecise and varying sawtooth rise time between voices ? I doubt it. Some parameters are critical, others can vary and offer dynamic changes pleasing to the ear. And current technology allow a precise enough control to get all of that simultaneously.
As proof of that, the extremely precise filter cutoff frequency control on the REV2 allows quasi-perfect keyboard tracking across a very wide range and on all 16 voices, which was impossible to get on any 33 years old synth, no matter how well a calibration could be done on it.

All that being said, maybe some of my critical parameters aren't as critical for some people ? Probably. But the 50% duty cycle one is as critical for awelchel (the thread starter) as for me. 

[eXode]

The DCO only gets it pitch from a digital clock, the actual waves shape is generated on the analog side, so correcting imperfect waveforms is not just a matter of some simple calibration routine or solved with high resolution/clock speeds.

[aeonn]

I think that some users forget about the very first purpose of the Prophet Rev2 as an instrument : play music.

I totally understand when a bug slows you down during your creation process and it’s legitimate to want it solved ASAP. But here we are talking about an insignificant imperfection that actually makes the Rev2 more organic than other instruments.
Sometimes we often get lost by using our eyes more than our ears. At the end of the day, the audience doesn’t care about how far you have set the waveshape setting on your synth, as long as it sounds good. And stop pretending that people notice such thing, because nobody actually cares about that.
Remember that the Prophet Rev 2 is a musical instrument. Not a measuring tool or else. It’s meant to create “music”. Not only pure tones. It’s meant to be heard, not contemplated through an oscilloscope.

Time to go back to creating actual music with it

[extempo]

It’s also good to point out that this is not a bug report thread. I heard back from OP in support, and he just needed to update his OS and perform an additional calibration. Last I heard he was happy with the duty cycle of his squares. 

This happens a lot, where someone encounters a difficulty, signs up to the forum to ask for help, and then we get it resolved in support. The OP often doesn’t follow up on the forum because they either forget or are too busy getting back to music making! I try to pop in here when I can to give these threads some closure.

[AlainHubert]

Sorry for my previous rant. Aeonn is right, it should be all about the music.

[discorules]

What do tool / vst do you guys use to see the waveform of the note ?

[guyaguy]

What do tool / vst do you guys use to see the waveform of the note ?

My MOTU interface came with CueMix which includes an oscilloscope. I'm sure there are free oscilloscope plugins too.

[Gerry Havinga]

It’s also good to point out that this is not a bug report thread. I heard back from OP in support, and he just needed to update his OS and perform an additional calibration. Last I heard he was happy with the duty cycle of his squares. 

This happens a lot, where someone encounters a difficulty, signs up to the forum to ask for help, and then we get it resolved in support. The OP often doesn’t follow up on the forum because they either forget or are too busy getting back to music making! I try to pop in here when I can to give these threads some closure.

Thank you very much, I really appreciate that you guys are doing this. If the end user "forgets" to update her/his forum message it is not more than fair you add a comment to the thread explaining what happened and how/if it was resolved.