Midi Clock Instability

I’m feeding Midi Clock from Nuendo through a MOTU Midi Express 128 to three outboard effects units (Lexicon PCM-91, MPX550, and TCFireworx) just to sync delays to the Project tempo and to select patches.

I’ve noticed that the tempos on the effects units vary slightly from the BPM tempo set within the Nuendo project. For example, if the Project is set to 148, the tempo on the effects with vary from 146 to 149. Each effect unit varies on its own, even though they all get their clock from the same Midi Out - they do not all vary by the same amount at the same time. This makes me think that it could be the effects units themselves that are unstable.

I would obviously like to see a rock-solid ‘148’ displayed on all three units all the time, but is that realistic?

Normally, the Midi clock goes from the MOTU to a ‘1-In 4-Out’ mains-powered MidiMan box and then on to each effects unit via separate Midi cables, but I’ve tried going straight from the MOTU to each effect separately and also tried daisy-chaining the three units with Midi-In/Thru. Also tried bypassing the MOTU completely and feeding Midi clock through the RME Fireface audio/midi interface. Also changed all midi cables and cleaned all plugs and sockets with contact cleaner.

Nothing makes any difference, which makes me think that the issue may be Nuendo or PC based.

The variations in tempo are momentary so there are no dramatic tempo changes to the effects, but I do sometimes get the feeling that the project tempo is not rock-solid.

Does anyone have any recommendations on how to eliminate this issue?

Perhaps one answer would be to not look at the effects units, ignore the fluctuations and just get on with it!

Another answer may be to abandon the outboard and just use ITB effects, but I’d like to keep them going to lessen the load on the CPU, and just for old time’s sake.

Computer generated MIDI clocks suck, there’s too much jitter…on PC more than on Mac. Both are unacceptable especially when clocking external drum machines.

This does away with it: http://www.s-n-d.com/acme4_a.html

I’ve looked at that and also the E-RM Multi Clock. They are both expensive and I’m not sure how they handle BPM’s to 3 decimal places ( like 120.999 for example ) that Nuendo caters for, nor whether or not they can cope with tempo or time signature changes changes within the same project.

ITB is looking more and more attractive, although that may require a PC upgrade for me.

The way this works: you send a 16th note pulse from an audio track to clock the MIDI syncronizer.
There’s almost no jitter at all, hence you get sample accuracy as per your audio pulse. That should do just fine.

If you don’t need a multichannel MIDI clock, take a single channel one and pay way less.

the clocking signal is actually 24 pulses per quarter-note and the jitter is just 1 sample (at 48kHz).
This means it will output any tempo you want, with audio-level precision.