Crackly aftertouch?

[bigcatrik]

On my Minibrute there's crackling when I invoke cutoff through aftertouch on high notes (MP3 attached).  It's the same when using the MIDI in.  Is this normal or is there a setting I can adjust to get rid of it?

[yusynth]

I have just listen to your sound sample and I don't understand what you mean by crakling. From what I hear all is normal, there is an increase in high harmonics because the filter is opening up. It sounds about the same as if you were tweaking the cut-off knob, doesn't it ?

[bigcatrik]

Thanks for the response, but, yes there's a difference between using keyboard aftertouch and the cutoff knob, as in my attached file which is as follows:

filename: MiniBrute_aftertouch_vs_cutoff_knob_crackle.mp3
two keyboard aftertouch notes (noisy during sweep up and down),
two cutoff knob notes (clean),
two more keyboard aftertouch notes (noisy),
two more cutoff knob notes(clean).

The keyboard aftertouch is MIDI?  Maybe it's a MIDI resolution issue.  I get a less noisy sound with my wind controller's breath sensor outputting aftertouch (through MIDI) than with the keyboard aftertouch, but still not as smooth as the cutoff knob (which is, of course, analog).  I've recorded the MIDI output of the keyboard aftertouch and my wind controller's aftertouch and the amount of noise decreases with the smoothness I see in the MIDI view.

I'm really most interested in using the MiniBrute with my wind controller (EWI4000s) so I'm trying to get it to work the best possible, or figure out if there's a compromise I'll have to accept.  Being able to plug a MIDI cable into an analog (or even digital) synth and play it with a wind controller without having to do extensive reprogramming is quite amazing.

I should note that this happens predominantly with high notes, octaves "+1" and "+2".

[Bruno@arturia]

I guess it' indeed a midi and aftertouch sampling rate limitation. large values jumps will for sure generate clicking noise on the filter.
Not sure you can get a much better result

[T3k]

I think the "crackle" you hear is the stair stepped values controlling the cutoff.

The cutoff knob is an analog pot controlling an analog filter, but the aftertouch is basically standard MIDI resolution control data.

Tiny pressure differences on your aftertouch will result in fast stepping through a larger range of cutoff. I'd guess those discrete values zipping by are the crackle.

Minibrute has an analog sound path but a few controls are digital.

[beefinator]

How does the mod wheel (mapped to cutoff) sound in comparison to the aftertouch?   Should be equivalent.

T3k's right, the cutoff absolutely will sound cleaner and smoother.  It's a knob directly wired into the analog circuitry.

MIDI's digital, quantized.
At some point they decided that 7 bits was enough resolution for MIDI control messages.  So aftertouch and mod wheel and other standard MIDI CC messages (pitchbend being a notable exception) will always be "steppy".

[Bruno@arturia]

On Minibrute the modwheel and pitch bend have a 9bits resolution. Midi allows up to 14 for modwheel and pitch bend. The aftertouch is only 7 because of midi limitation.
So the aftertouch is usually more quantized than modwheel.
Beside resolution, sampling rate is important too. It's the same for every controls in MiniBrute, but you move the modwheel across it's full range in at least several hundreds ms, but aftertouch could be much fast, so it gives less values across the range. 

[bigcatrik]

But ...

My DSI Evolver takes standard MIDI aftertouch (0-127) and, through its filtered input, delivers a smooth filter sweep as demonstrated in the attached MP3.  What does Dave Smith know about MIDI that others don't?  Even my Mg LP crackles when fed 7-bit MIDI, and it cost three times what the MB or Evolver module cost.

[T3k]

There's no law saying you have to take 127-step data and directly couple it to parameter control.

You could use slew or digital interpolation or dual messages (for doubling res) any number of schemes to smooth out behavior. It depends what you do with your MIDI data. Dave Smith is the godfather of MIDI and he implements it extremely well on his instruments.

I'm fine with 127-step aftertouch. Heck, aftertouch itself is pretty amazing feature on a low-priced synth.

[bigcatrik]

I'm fine with 127-step aftertouch. Heck, aftertouch itself is pretty amazing feature on a low-priced synth.

Yes, the MiniBrute is amazing, but as a new owner I'm bringing up questions to make sure I get the most from it.  Sometimes a fresh set of eyes on something can be helpful.  Often companies are looking for ideas for firmware updates, etc... ;-)

[bigcatrik]

Possible solution:

Applying judicious EQ seems to calm the crackle, as in the brief attached file* (how can I make a post without an MP3 attached?).  It starts out crackly, then I fade the EQ down to eliminate it, then bring the EQ back up and it comes back.  The crackle seems to be low frequency so this should work on higher notes (and I should be able to automate it in FL-Studio to sound better than the quick test in the clip).  Low notes sound smooth as is and wouldn't need EQ.

Hooray.  I was thinking of returning the MiniBrute but what would I replace it with?  No other synthesizer has made me like and want to use a triangle wave (Metalizer!).

*EDIT:  Doesn't look like the file got attached.  The text gets the idea across.