CV->MIDI Problems

I’m having some MIDI issues with external synths. At first I suspected the synths themselves, then the USB interface. But now I think it’s the CV->MIDI module.

The problem can also be recreated without external synths - i.e. only with VCV rack modules.

To do this, a sequencer (FOUNDRY) sends a simple sequence (C major scale up and down) to CV->MIDI. CV->MIDI uses a virtual VCV device (VCV Rack input 131:0) MIDI->CV receives the signals and passes them on to a VCO-VCF chain so that you can hear something. In addition, CV, GATE from FOUNDRY and CV, GATE from MIDI->CV are output on an OSCILLOSCOPE. The MIDI messages are displayed by MIDI-MON.

If everything goes well, you can hear the C major scale and in the OSCILLOSCOPE the CV and GATE lines run parallel. MIDI-MON shows the sequence on-off-on-off…

But at some point there will be misfires. You then hear that and in the OSCILLOSCOPE the lines no longer run parallel. This means that the input from CV->MIDI is different than the output from MIDI->CV.

Here you can also see the reason. There are two “note on” messages one after the other. If the appropriate “note off” is received, it will be corrected again.

The problem doesn’t always occur and it seems like it depends on CPU load.

I’m using VCV Rack 2.4.1 Linux x64 on LMDE 5 Elsie and Ubuntu Studio (occurs on both platforms).

Here is the patch for it: synth2600-2-midi-prob-6-no2600.vcv (5.7 KB)

In order to set the Virtual VCV Rack MIDI Decive, you must first select an existing MIDI device in MIDI->CV. A virtual device is then available in CV-MIDI and then also in MIDI->CV and MIDI-MON.

Does anyone know the problem and perhaps has a solution?

I know this might not help, but I tried your patch in Ubuntu (22.04.3 LTS) and was not able to reproduce the bug. It looks like it will be hard to track down if it’s intermittent in nature, but I hope you will get to the bottom of it.