Me or Mooer?

[Mark Hammer]

I just picked up a Mooer Super Bender - their Whammy-type pedal - dirt cheap.  I mean stupid cheap.  I guess the guy had no means to test the power supply, and simply figured it was the pedal that was busted.  Plugged in a different supply and away we go.

But here's the thing: it's juuuuuusssst a bit flat.  If I set it to bend pitch an octave up, it gets almost 99.7% there, but never really nails it.  A year or so ago, I bought a Mooer Pure Octave pedal - their Micro-Pog-type pedal - 2nd hand.  And it too seems to be juussstt a bit flat for octave-up, and a bit sharp for down octaves.

If it was just the Super Bender, I'd think maybe it's me, because the unit doesn't provide original and bent pitch at the same time, so you can't compare.  I listened to demo Youtubes, and I heard the same almost-but-not-quite pitch.  But the Pure Octave does let you blend input signal and derived signals, and the imperfect intonation is driving me nuts.

Has anyone else experienced the same thing?  And is there anything one can do about it to rectify things?  I can't believe Mooer would consistently produce pedals that can't nail a simple octave.  I'm not exactly David "Perfect pitch" Burge, but even a doofus like me can hear the poor intonation, and it grates on you like that bad final note in the roadrunner cartoon.  Is there possibly a trimmer inside such things to tune them?

[toneman]

maybe it hasn't been calibrated properly(?)  I had a similar prob with an mxr pitch transposer.  several generations apart in technology, but similar in principle. 

[merlinb]

Maybe you could test it by playing a pure tone into the mooer from a sig gen, and play a tone of twice the frequency into a different amp, simultaneously. If they're not the same you should hear a beat frequency, no?

[Ben N]

Or scope.

[Digital Larry]

Make sure you are not falling off a cliff while wearing rocket skates, this can introduce a Doppler shift which some people find displeasing.

[paul.creedy]

I bought a s/h Mooer Pitch Box out of curiosity once, the pitching on that was awful, so I quickly moved it on.

[Mark Hammer]

Maybe you could test it by playing a pure tone into the mooer from a sig gen, and play a tone of twice the frequency into a different amp, simultaneously. If they're not the same you should hear a beat frequency, no?

The Pure Octave permits that very test, by allowing adjustment of octave, sub-octave, and straight sound level, and the beats drive me nuts.  I can't bring myself to use it anymore.

[anotherjim]

What pitch shift method is the Mooer using then? Detecting by averaging (like a tuner) then resampling up or down?

[Phoenix]

There is also the possibility that it does, in fact, produce a perfect frequency doubling - a true octave. Unfortunately, that is not what a guitar produces, nor any stringed instrument for that matter. This is thanks to inharmonicity - the phenomenon of string harmonics getting progressively sharper as their order increases. This is actually the true main cause of the need for string compensation in guitars, not action as is commonly believed (though that is also a factor, it's just not the dominant one). It is caused by string stiffness. A perfectly flexible string would produce pure harmonic multiples, but we live in the real world, so if we were to intonate the 12th fret to a perfect doubling of the open fundamental, it would actually sound flat compared to the 1st, 2nd, 3rd, etc. harmonics present in the open note. This is also the reason for "stretch tuning" of pianos, something I'm sure most people here will have heard of. A great example of how pronounced this effect can be is if you've ever been in a music hall with both a grand and upright piano. Even if both pianos are tuned perfectly, sound in perfect tune by themselves and their middle C's are a perfect match, when played together it quickly becomes apparent that they are not in tune with each other. This is because due to its smaller size, a typical upright will have shorter, and therefore thicker strings than the grand. The result is the lower octaves of the upright are flat with regard to the grand, and the upper octaves are sharp.

So it's possible that this could be at least part of what you're hearing. A signal generator and tuner should diagnose this quickly for you.

[Mark Hammer]

So it seems like the experiment I'm going to have to do is to is fire up my Micro-POG, my Pure Octave, the Super Bender, and the tuner in my M5, and see how close to the desired pitch each comes.

[vigilante397]

I have a Pure Octave and I've never actually had any problems with it, I've always been happy with the sounds it gives me.

[Rob Strand]

So it seems like the experiment I'm going to have to do is to is fire up my Micro-POG, my Pure Octave, the Super Bender, and the tuner in my M5, and see how close to the desired pitch each comes.

I haven't used one but if all modes are wammy-able maybe the footpedal attachment has slipped on the pot and it never gets to the full extreme.

Another more evil problem is the pot is powered from one power supply but the microcontroller inputs are supplied from the micro's own reference voltage (or supply).  Due to tolerances or a misadjusted power rail voltage the two have become out of whack,  effectively making the pot look off and never getting to maximum.

If the pitch is off in a non-wammy-able mode then that's a trickier problem to solve as you need a circuit to work out where things can go wrong.

I noticed there's green and purple box versions of that pedal.

[Mark Hammer]

It's purple, which I gather is the Mk II model.

The control knob essentially lets you preview what the foot treadle will do at its maximum positions.  So if you pluck a note, and turn the knob so that the toe-down display shows "12", that signifies an octave up, and you hear that shift, as if you pushed the treadle down.  But is sounds a little flat when I do that.

I'm going to have to find some time this weekend to do the experiment I suggested.  And instead of my guitar, I'll have to use the precision signal generator I have.  I'll be sure to report back.

[Rob Strand]

The control knob essentially lets you preview what the foot treadle will do at its maximum positions.  So if you pluck a note, and turn the knob so that the toe-down display shows "12", that signifies an octave up, and you hear that shift, as if you pushed the treadle down.

It could still have a problem. 

If the display is rounded internally it might display 12 but internally it's not quite 12.
For example integer rounding would show 12 for 11.5 and above   One digit rounding could show 12.0 for 11.95. Anyway, that type of thing.   If you can quantify the shift by measuring the frequency then it might be possible work out the expected display value from the amount the frequency is off.

Presumably 12 means 12 semitones, so
f_shift / f_fundamental  = 2 ^ (internal_value / 12) for shift up
f_shift / f_fundamental  = 2 ^ (-internal_value / 12) for shift down
when internal_value = 0 there's no shift when internal_value = 12 you have an octave.

In your case f_shift will be the measured frequency and so you can back calculate the predicted internal value,

internal_value = 12 * log(f_shift / f_fundamental)  / log (2)  ; doesn't matter if use use ln() or log10().

[Mark Hammer]

I think the display is essentially showing the user preset fixed intervals, rather than measuring anything.  So if it says "12", that's the octave preset.

But again, I'll have to do my own measurement this weekend.

[Rob Strand]

think the display is essentially showing the user preset fixed intervals, rather than measuring anything.  So if it says "12", that's the octave preset.

Sometimes you have to use your instincts about what is actually going on under the hood.

[Mark Hammer]

I took it apart today, to find that the foot treadle operates a pot.  I thought "Maybe if I move the pot over just a little the way one does with wahs", but it would seem the pot values are quantized by the circuit, rather than read directly.  Still have to do "the experiment", though.  Trying to round up enough 9V supplies  with sufficient current to power all those digital pedals..

[anotherjim]

I've never heard of it in simple pedals, but some digital designs do have a calibration mode. Usually, this means operating some button during power on until it displays some visual cue, then you move the control to one extreme, press a button, move it to the opposite extreme and press again and it's done.

A while ago I bought a Behringer FCB1010 and both expression pedals failed to output MIDI cc to the full 127. I got it replaced but the new one did the same. I then found out it had a calibration procedure that no one thought to include in the masses of multilingual documentation it came with but could be found online. That fixed it. Those pedals work optical LED-LDR controls but would be the same for pots.

[pinkjimiphoton]

mark,
try holding down the bypass button while powering up. i seem to remember reading something about calibration or something. did ya try the mooer website or a google search for the manual?

[Mark Hammer]

I did write to their service desk and describe the issue.  Their response indicated there was nothing I could do.