Monophonic MIDI Pitch Bend Curve Converter - Lin To Exp

midi
#1

Here's a mono MIDI PB curve converter. It forwards all MIDI traffic from USB MIDI Host port to MIDI DIN except Pitch Bend data. It transforms linear PB input into variable exponential curve, separately adjustable for positive and negative values.

What for is this useful? Well, there are hardware synths which respond to Pitch Bend data in non-linear fashion. Mine is Gotharman's anAmoNo X which response is logarithmic. I know Nord Lead series is 'suffering' from this non-linear PB syndrom too (yeah, I know it's because of their special Pitch Bend stick).
With linear PB data from Linnstrument, PB slides are 'out of tune' (except the max PB position which tunes back to right pitch). To straighten this curve, I had to invert it by applying exponential curve. I just tuned the curve by ear and it works for my purpose.

I don't do Axoloti patching on regular base and believe that there is more elegant way to patch this. Feel free to share your suggestions for improvement. I tried to comment the logic within the patch.

Credits go to all authors of modules/blocks being used respectively, thank you guys!

Edit: This patch should be connected between (USB) MIDI controller with linear PB output and synth with logarithmic PB response.

axo_pb_curve_lin2exp.PNG765x573 39 KB

midi_usbh_to_din_PB_curve.axp (6.6 KB)

#2

Can you explain why the pitchbend from the linnstrument doesn't work? It should be linear, shouldn't it? When I apply that to a pitch input, why should it be wrong?
Just curious, because I have a linnstrument on the way to me and wanted to use axoloti as my sound module.

#3

Oh, yeah, maybe I should've describe that better. Linnstrument and Axoloti as a sound source is fine. LS has linear Pitch Bend. Axoloti synths respond correctly unless you program otherwise.

My patch is an aid for hardware synths which respond to Pitch Bend following logarithmic curve. Luckily these are AFAIK rare and usually have their own reasons for that. It can sound more musical in combination with specific hardware (Nord Lead pitch stick) and while using PB wheel for traditional manual vibrato action.

Here's the example of issue. anAmoNo X has PB range of 12 semitones. I set Linnstrument's PB range to 12 semitones too. But when sliding i.e. 6 semitones (or anything from 1 to 11), the audible pitch is not corresponding to slide position. Sliding fully to 12th semitone gets back in tune. It's like a 'de-tune' curve that needs to be straighten.