beat frequency not consistent

[aldred]

I've been watching this video here ....

https://www.youtube.com/watch?v=0z7kbGZ2sPg

From about 7:50, he's getting a really regular beat with the beat frequency knob. I can't get anywhere near this consistency across the keyboard. No matter how much I tweak the Frequency knob around 0, the top C beat is about twice as fast as the bottom C. It's nowhere near as pronounced an effect as the video either.

Anybody else experience this?

Thanks
Mark

[breun]

Is your OSCILLATOR 2 FREQUENCY centered?

The Sub 37 v1.1 manual mentions the following on page 26 when discussing beat frequency:

NOTE: For this reason, if you want a constant beat frequency at all pitches, make sure that the OSCILLATOR 2 FREQUENCY control is centered. If you want near-absolute unison between oscillator 2 and oscillator 1, make sure that the BEAT FREQUENCY control is also centered.

[aldred]

Yes. I have the Frequency knob centred. The beat frequency still varies across the keyboard.

How is yours? Can you get it perfectly matching from low to high C?

Thanks.

[DrJustice]

Since this sounds like a pitch tracking issue, you could try calibrating the oscillators. GLOBAL MENU >> CALIBRATION >> NOTE CAL >> ... (manual page 48).

[aldred]

Thanks. I just ran calibration and it seems to be a little better, but there's still a very noticeable difference playing intervals greater than one octave.

Is Beat Frequeency meant to make the beat exactly and accurately the same tempo over the whole keyboard range? Or is it meant to make the beat roughly the same, with differences creeping in as you go up the keyboard?

How does yours sound? Is it exact?

Thanks
Mark

[bichuelo]

It seems consistent in my unit... anyone else?

[DrJustice]

Good thing you made this thread, Mark - because I just tested and found that my Sub 37 needed a calibration...

Before calibrating, the beat frequency increased with increasing pitch, and the middle position of the BEAT FREQ knob had beating of around a Hertz or a half. After calibration, the oscillators track perfectly and the beat frequency it's pretty consistent over the whole range (there is some variation, but not much).

So, thanks for bringing it up

[aldred]

Thanks for the replies.

On my machine, it seems fairly consistent if I just sit down and play something, but against a metronome you can hear the difference.
I've contacted support so I'll post when the reply comes. There's no place in the manual that says whether it's meant to be a precise function, or something that will just give you a rough match across the keyboard.

[mikeh11]

Here is my experience: the Beat Freq control depends on first getting a beat-free sound across the keyboard. It doesn't override the Tune control, but offsets it a little bit. So, if the sound is already beating, the Beat Freq control won't control that.

Steps:
- put the Beat Freq control to zero
- use the Osc2 Frequency control to tune the two oscillators for no beats at all, anywhere
- verify no beats at the top and bottom ends
- maybe even use KB Octave to shift up an octave and tune there (?)
- now the Beat Freq Hz control should behave as it says

If you can't get a "no beat" sound across the keyboard when Beat Freq is zero, then when you go to use Beat Freq, it will look like it behaves incorrectly. If the oscillators are already beating at 1 or 2 Hz, then the Beat Freq control will appear ineffective, I think.

If you get differences across the keyboard, then maybe the oscillators weren't tuned close enough, or maybe there's a tracking problem, or maybe the unit needs pitch calibration? (which you've done, I know).

If there's a difference in beat frequencies between the +1Hz and -1Hz settings for the same note, then the "unison" wasn't quite right. It would mean that Osc2 was too high or low, and detuning one way or the other with Beat Freq makes it worse or brings it back in tune.

(I supposed there are hardware explanations, too, like the knob not being on the shaft "just right", or the pot slipped, or whatever, but if it rotates from -3.5 to +3.5 then that should be OK, yes?)

Is Beat Frequeency meant to make the beat exactly and accurately the same tempo over the whole keyboard range?

I think it should be fairly accurate across the keyboard.

Also, the pot values plateau at the ends of their travel, so there could be some differences at the extreme values. I mean, setting Beat Freq to "3.2" might really be "3.09" or "3.4" or something. But I would expect the "1" and "2" settings to be pretty much what they say they are.

This seems to be true for the Sub37 here. When I've got the oscillators playing well with no beats, and the Beat Freq dial points to +1Hz, I get about a one Hz phasing effect. At +2Hz, it's twice as fast (by my inaccurate mental metronome). This is across the 3 octave keyboard.

I guess it _could_ be a pot calibration problem with the Beat Freq control... I'm pretty sure there were forum posts that talked about calibrating the pots. I don't have a handy link to it, though.

Or is it meant to make the beat roughly the same, with differences creeping in as you go up the keyboard?

That sounds to me like maybe there wasn't a beat-free sound at the top end when the Beat Freq control was set to zero. If it's good at one end but not the other, I'd expect differences in beating at the two ends when Beat Freq is set back to zero. If you can get "unison" tuning across the keyboard, then the Beat Freq should work great.

I just ran calibration and it seems to be a little better, but there's still a very noticeable difference playing intervals greater than one octave.

Are you using Duo mode? That's what I think of when you say "intervals".

Does it depend on what octave the oscillators are at? Is it independent of the KB Octave setting? Just questions for curiosity's sake, as I'm not sure what we could conclude from that information. I would guess it's harder to get good "unison" tracking on the higher ranges, although maybe that doesn't apply to the Sub 37. (memories of tuning old analog gear)

Disclaimers: I'm no expert on this; I hope other folks jump in with better descriptions and solutions. And my apologies for wasting your time if you're already tuning excellent unisons across the keyboard before adjusting Beat Freq.

[mmarsh100]

And as Demon_Dan pointed out in another post, you can enable sync between the oscillators to eliminate *all* beating...

[aldred]

Thanks. I appreciate the help.

My starting point is as beat free as I can get it across the keyboard. It's almost impossible to get rid of the beat completely, but I'm sure it's as close as it can be. I've also tried tweaking the Frequency around zero with Beat set to see if that gives me more consistency, but there's no sweet spot on the Frequency pot.

If there's a difference in beat frequencies between the +1Hz and -1Hz settings for the same note, then the "unison" wasn't quite right. It would mean that Osc2 was too high or low, and detuning one way or the other with Beat Freq makes it worse or brings it back in tune.

I hadn't checked for a difference between +/- values. When I did, I found that -2 gives a slower beat than +2 for the same note. Not by much, but again noticeable.

Are you using Duo mode? That's what I think of when you say "intervals".

No, I haven't touched Duo mode.

Does it depend on what octave the oscillators are at? Is it independent of the KB Octave setting?

Actually, I noticed something strange. WIth the keyboard middle octave setting (no lamp lit), the higher the key the faster the beat. But if I go up an octave it's the other way round - the high C is slow, low C fast.

No reply from support yet.