I’m running my Elektron Digitakt as a midi slave from ableton midi clock.
The timing is extremely accurate, but if I use a more generous 512 samples of latency, to stop my processor getting hot, the timing is still locked, but late.
The only latency the locks both sequencers is 32 samples with a latency of 3ms… if I run a few Ableton synths my processor struggles.
What should I do? There’s no latency control on the Digitakt is there?
There is latency control in Abelton:
Set up your system as you intend to use it. Record the DT into a track. Have the DT play something on the beat, and with a clear attack transient. Now zoom way in, turn off the grid (cmd-4), and select from the start of the transient back to the beat. The status bar on the bottom will tell you how many milliseconds this is. Now set the MIDI Clock Sync Delay to negative that number.
There is also a latency setting per individual track you can adjust within Ableton.
Just to confirm you also have ‘plugin delay compensation’ activated?
Edit. Disregard. Shouldn’t be relevant at DT not a plugin yet
Many thanks you guys - I will give it a go and report back
Well after some rather depressing sessions of timing accuracy I have some information to report back.
I am using Ableton 9.7, Midi Clock out into the Digitakt. This controls two analogue synths, an SH101 and an original MS20.
I put the Buffer Size on 256 - this made the output latency at 7ms
I then changed the Midi Clock Sync Delay to -7 and this seemed to tighten everything up.
The biggest issue is the tempo accuracy from Ableton. Its all over the place. It can be + or - 1bpm, sometimes even more. I have no idea how to tighten this up.
Once again I am leaning towards going total hardware and forgetting the computer all together, as it once again proves they are so complex that they can’t keep anything midi in time. Pisses me off no end… 
We haven’t even discussed what audio interface you are using? Latest drivers etc? Mac or PC? Critical to make sure you are running the correct and latest drivers for your interface.
How are you monitoring these signals? Back through Ableton or direct from audio interface?
There are so many other factors to check
Are you hearing actual tempo variation between the DT and Ableton? Or are you just looking at the BPM on the DT display jitter up and down?
If you are inferring this from the display on the Digitakt, then this is nothing to worry about. All MIDI clock slave implementations must deal with the somewhat jittery MIDI clock stream. They generally implement a form of phase locked loop in software, because the aim is to lock the frequency and phase of the internal sequencer to the master clock. There are a number of tuning parameters in such an implementation representing different tradeoffs. Since displaying BPM is really a secondary consideration, the turning isn’t for that. I implementations that show a stable BPM, it is generally a separate smoothing for display of the actual internal state.
Yes it’s true, it’s standard to see a digital BPM display value fluctuate up and down on a bit of gear, when being clocked by another.
If you can’t hear it out of sync then it is probably being clocked fine
I have the same issue here. bpm fluctuating a lot! and it is not only visible, but audible too when I use delay on melodic stuff. it pitches up and down because of the tempo fluctuation…