Beat Frequency not consistent

Polyphonic Analog Synthesizer
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mattculpin
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Beat Frequency not consistent

Post by mattculpin » Mon Apr 08, 2019 4:57 pm

Had my One for a month now, still exploring. However, I find a strange thing happening to the beat frequency. It changes depending on the note you play across the keyboard. My only reference for this is the Sub37 I have. With 2 OCS's active, I can set the frequency to beat how I want it and it will change to keep the consistency across a fairly wide note range. However, on the One it loses the nice beating over just a couple of octaves.

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AlakaLazlo
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Re: Beat Frequency not consistent

Post by AlakaLazlo » Tue Apr 09, 2019 6:31 pm

Mine does that too. I assume it's one of the tuning bugs.

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till
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Re: Beat Frequency not consistent

Post by till » Wed Apr 10, 2019 5:09 am

My 2 cents (and beating is often well below 1 musical interval cents):
Compared to a vintage, fresh and well calibrated analog polysynth, the Moog One has the best stabile pitch I ever encountered. In fact it is sometimes too stable. So I often use the pitch variation parameter (in the MORE menu of the UNISON section works even without unison used) to get a more analog flavour. Without the pitch variation I get 100% perfect octaves with no detuning from one note to another. Slightly variation get the right rolling and moving sound when playing octaves with the left hand.

I remember even the voices of a Memory Moog shown on the german music fair in the early eighties was very slightly different tunes for each voice. This is part of a magic sound of the analog world. And the Moog 901 oscillators are absolute not 100% pitch stable. But they get you THE sound due to this slight to medium pitch variations and their imperfect waveshapes.

Beating is a very subtile thing to add. I can't think of one analog polysynth besides the Moog One offering it.
I rather have a living sound character than a "perfect" VA like and lifeless character.

Historic view: On the original Moog 901B oscillators it was added rather than the typical detune, due to the fact, that each of the 901B oscillators did not feature it needed own exponential converter (the 901A did this for one to three 901Bs). There was simply no way to add detune to a 901B module. Later designs by most analog synth used one exponential converter per oscillator. And to the detune was added to allow musical interval rather than fixed frequency offsets by the beating parameter.

And btw: my filters are very well calibrated. I can play polyphonic using the ladder filter self oscillation in the mid 5 octaves. Try this on any other analog VCF polysynth. Most analog polysynth VCFs will be very much out off tune over 5 octaves and the tracking variation of each single voice and its own filter circuits.
keep on turning these Moog knobs

Sequence:
Prodigy * Minimoog (1979) * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog reissues with MUSEs * One

Alexander Krieg
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Re: Beat Frequency not consistent

Post by Alexander Krieg » Fri Nov 15, 2019 7:42 am

AlakaLazlo wrote:
Tue Apr 09, 2019 6:31 pm
Mine does that too. I assume it's one of the tuning bugs.
for me the beat Frequency function is unusable, cause the effect changes in that way that the deeper the note is the more it's out of tune.

amyristom
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Re: Beat Frequency not consistent

Post by amyristom » Fri Nov 15, 2019 9:25 pm

AlakaLazlo wrote:
Tue Apr 09, 2019 6:31 pm
Mine does that too. I assume it's one of the tuning bugs.
I can also confirm this behaviour, tested it on my Moog One (firmware version 1.1.0). The main "feature" of the beating frequency feature is that the beating (or maybe to say it easier to understand: the detuning) between two or more oscillators stays consistent / the same no matter how high / low the notes are that are being played.

On a "normal" analog oscillator the noticeable detuning between two or more oscillators (by using the frequency knob on the synth) increses when playing lower notes and decreases when playing higher notes. The "beating" feature archives that the amount of detuning between the oscillators stays the same no matter which notes are being played.

That being said, this is not really the case on the Moog One (with firmware 1.1.0, had not tested older firmwares). While dialing in a nice little detuning between two oscillators on the middle range of notes with the beating knob, normally the amount of detuning should stay the same no matter which notes are being played. On the Moog One instead the lower notes suddenly are sounding a lot more detuned than the middle range oder high range notes. And this should not happen! It is THE feature of the beating functionality that this does NOT happen.
On the other hand, when not using the beating knob and using the frequency knob instead for archiving a little detuning between the oscillators the tuning is OK on the lower notes, too.

So I would say this is definetly still a tuning bug!

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TabbyCatte
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Re: Beat Frequency not consistent

Post by TabbyCatte » Wed Nov 20, 2019 2:49 pm

I can confirm this as well. The maximum effective range is about an octave + one half, anything on either side of that and it descends into quarter-tone dissonance.

Thing is, I'm not sure about the spec for beat freq. The units on the front panel are in Hz and not semitones, which seems weird to me...because Hz are not linear (the distance between semitones, in Hz, increases as you go up the scale). So if you specify a fixed offset in Hz, against a non-linear scale, it will by definition go out of tune with itself.

This would explain why the lower notes sound out of tune - the distance between lower notes in Hz is less than the distance between higher notes, so the offset would appear more prominently.

...unless someone can tell me I've got it all wrong :wink:

I'm starting to wonder if the goal is to create "beats" in the purest sense of the word (i.e. the psychoacoustic phenomenon where you hear a distinct, periodic wobble), and not purely to offer some detuning. Would be nice if we could have an expert confirm.

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till
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Re: Beat Frequency not consistent

Post by till » Wed Nov 20, 2019 8:06 pm

Yes,
the beating parameter has to be linear. So the musical detuning is more emphased in lower range be definition.
Detune is exponential like our typical musical scales and octaves. So this sound in harmony.
But if you use real small beating values, the beating sound very usable for small tempo constant oscillator beatings across the keyboard range.
If you combine the detune and the beating, you got interesting things. especially if you use them in different "direction"/"polarity".
But yes, my Moog One is always, even without detune or beating used a bit off in pitch in the lowest octave of the keybed at 16" range oscillators. And the voices are not 100% identically in pitch anyway. But they are way better in tune than most vintage poly synths with real analog VCOs.
keep on turning these Moog knobs

Sequence:
Prodigy * Minimoog (1979) * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog reissues with MUSEs * One

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TabbyCatte
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Re: Beat Frequency not consistent

Post by TabbyCatte » Sun Dec 22, 2019 2:49 pm

Thanks for the reply, Till. (Sorry I am not getting reply notifications despite checking the preference a million times!).

I've read up on other implementations of the "beat" approach to tuning, and it seems the beat frequency usually tracks the keyboard. Again, the use of "Hz" for the units bewilders me here - as the listed range is +/- 7. Do they really mean 7 Hz? This would mean at C1, a value of 7 would be 32Hz --> 39Hz, which is almost a major third (!).

I'm not in front of the One at the moment but I'm going to experiment with this, to see if I really get a third when playing C1...if not, I suspect it's not tracking in a predictable way.

[UPDATE]
OK I tried it on a scope, and it's true - full Beat Frequency at C1 (or C0 non-MIDI) is almost a major third, and it is a solid 7 Hz deflection across the whole frequency spectrum.

...which causes the incongruities in the lower registers discussed earlier, and it is by design.

So the only lingering question is, why would you do this? Why would you implement a tuning regimen that will always be in tune in a very narrow band, and be out of tune everywhere else? I understand that the "beats" stay the same speed, but octaves in the left hand sound broken. Maybe this approach is for someone smarter than me :mrgreen:

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till
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Re: Beat Frequency not consistent

Post by till » Sun Dec 22, 2019 5:32 pm

For some slow beating like up to 0.5 Hz, the low octaves are not out of tune too much to sound out of tune.
This beating frequency thing worked fantastic on the linear VCOs of the original Moog Taurus and then again on the Taurus III and all following Moog synths. So this is not THE problem of out off tune low registers. Of cause, you can end up with a sound being totally off tune in the bass easily. But also too much detune would cause this too.
keep on turning these Moog knobs

Sequence:
Prodigy * Minimoog (1979) * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog reissues with MUSEs * One

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TabbyCatte
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Re: Beat Frequency not consistent

Post by TabbyCatte » Sun Dec 22, 2019 7:15 pm

Yeah I guess the magic formula is "a little bit" of beat, and combining it with normal freq detune. Despite having worked with many synths, this is alien territory...!

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till
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Re: Beat Frequency not consistent

Post by till » Mon Dec 23, 2019 6:44 am

I am often using a bit of beat and add some bit of detune in the other direction.
keep on turning these Moog knobs

Sequence:
Prodigy * Minimoog (1979) * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog reissues with MUSEs * One

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