[Bug] Audible glitch when using MIDI tempo linked to the delay time

[Kamil Kisiel]

The problem is really compounded by the shitty nature of the USB MIDI spec. Packets only get sent from the host to the USB MIDI device every 1ms. So it hardly even matters how good the resolution of your MIDI clock is in your DAW, your OS's USB MIDI driver is going to pack all those messages up into a single packet and then send it to the USB-MIDI interface every 1ms. There's no timestamping in USB-MIDI either, so the receiving device just has to make do with what it gets. In general there's always a 0.5ms jitter

 

[FractalAudio]

The problem is really compounded by the shitty nature of the USB MIDI spec. Packets only get sent from the host to the USB MIDI device every 1ms. So it hardly even matters how good the resolution of your MIDI clock is in your DAW, your OS's USB MIDI driver is going to pack all those messages up into a single packet and then send it to the USB-MIDI interface every 1ms. There's no timestamping in USB-MIDI either, so the receiving device just has to make do with what it gets. In general there's always a 0.5ms jitter

Yup.

However the OP is using "regular" MIDI.

 

[Kamil Kisiel]

Yup.

However the OP is using "regular" MIDI.

But if they are sending a clock from their DAW, that "regular" MIDI is just USB MIDI going to a USB-MIDI interface first, so USB is still involved even if not directly to the Axe-FX. It might actually make it worse depending on how that interface handles clock messages.

 

[FractalAudio]

But if they are sending a clock from their DAW, that "regular" MIDI is just USB MIDI going to a USB-MIDI interface first, so USB is still involved even if not directly to the Axe-FX. It might actually make it worse depending on how that interface handles clock messages.

True.

 

[unix-guy]

The problem is really compounded by the shitty nature of the USB MIDI spec. Packets only get sent from the host to the USB MIDI device every 1ms. So it hardly even matters how good the resolution of your MIDI clock is in your DAW, your OS's USB MIDI driver is going to pack all those messages up into a single packet and then send it to the USB-MIDI interface every 1ms. There's no timestamping in USB-MIDI either, so the receiving device just has to make do with what it gets. In general there's always a 0.5ms jitter

Well that probably explains the suckage I encountered with BandHelper on my iPad sending the clock

Would be nice to get the sysex for setting tempo on the Axe Fx III, which is really all I wanted anyway.

 

[psimon666]

Thanks for your answer, i'm gonna check this, but i don't think i am able to choose the MIDI frequency messages in my DAW (SONAR). but i'll take a look on this.
Yes, another thought was that my MIDI ports use USB : maybe there is a lack of accuracy inside the MIDI drivers, but i can do nothing against this.

Nevertheless, is there really no way to remove the unwanted pops ? Even if (time to time) my tempo toggles from 130 to 129 bpm i'm not sure someone can hear a tiny varaition of the delay time during a short period, so the problem does not really concern the accuracy of the bpm, but the unwanted pop sounds

My theory is that the variation of the tempo occurs when the delay FX has already started. So, the delay FX starts with a tempo, and ends with another, and this generates pops. One way to solve this, is to ignore the change of delay times while the current delay is still processing (i don't know if it's clear). Or keep the original tempo untill the end of the running calculations

 

[jcalama]

I just tested this to make sure everything is working properly and it is. However... it all depends on the accuracy of your DAW. If I set the BPM to 130 and the accuracy is 5ms it will occasionally go to 131 BPM on my system here. If I lower the accuracy to 2ms then it doesn't do that.

And this is as would be expected. 130 BPM is 2.167 beats per second. MIDI Clock is 24 messages per beat. So that's 52 messages per second or a message every 19.2 ms. 129 BPM translates to 19.38 messages per second. So your messages need to be accurate down to fractions of a ms.

So you need to find if there's a way to increase the MIDI clock accuracy in your DAW.

Can anyone suggest how I might increase the MIDI clock accuracy in my DAW (in this case, Ableton)...I have messed with the midi clock sync delay setting but it doesn't seem to improve the situation.

 

[sb-SG]

I am maybe getting to see a similar thing when I slave the Axe Fx to a HeadRush LooperBoard. This by 5 pin. As the loop cycles through finish / start there is a sudden blip in tempo from delay timing from the Axe FX but it sounds like more than a couple of BPM. I am still fairly sure this is courtesy of the LooperBoard but may be related? I am not sure its sending a straight clock at all.
Otherwise a slight variation in tempo in a DAW is something I can live with.