Depending on what the twitchy stream is doing - the Pulsar Buddy will closely follow a moving average of the tempo over two beats. The output tuplets will follow this smoothed temp, speeding up and down, surfing the tempo “wave”.
If you are feedbacking the clocks - then you should experiment with different scales of clock sync (1/4 to 1/32) to see how this affects the feel.
Clock following is a bit of an art, and there are many engineering tradeoffs to be made.
The current implementation measures the rate every ext. clock event, but then uses a moving average, two quarter notes wide, of that rate. The rate is then further adjusted by a phase locked loop (so the 1 stays the 1), tuned to converge over one quarter note.
On the one hand, you want things to track as fast as possible, so that quick BPM changes by hand are tracked directly… on the other hand many sources of sync clock are often jittery over the course of a quarter note. (Not just MIDI sources, I’ve seen this in modern DIN Sync sources as well!) My choices in the current firmware reflect this compromise… feels responsive without being jumpy to me when I play with it.
You could easily recompile the firmware with different time constants, making if faster or slower as you need! Happy to help if you want to try this.
Lastly, a note about displayed BPM - and this slight rant applies to displayed BPM on all systems that are slaved to some external sync:
tl;dr: Listen with your ears, not your eyes. Feel the groove. Don’t be a slave to numbers.
If you simply display the clock to a tenth of a BPM, most users will freak out when they look at it. If the clock system is measuring the time between, say, 24ppqn clocks (DIN24 sync or MIDI sync), and displaying the currently measured BPM - then a difference in less than 20µs is enough to make the display flicker between 120.0 and 120.1. Of course, you can’t hear such a difference: It would take more than a full minute of being at 120.1 for the attacks to drift by a 1ms… and in that minute things will have long since averaged out.
In Pulsar Buddy I have yet another filter just on the displayed BPM. This makes sure that it doesn’t flicker with steady clocks (which are none-the-less not jitter free) at the expense of looking a little (but not too much) laggy when the clock slews. By example, Elektron takes the other approach in Digitakt: It’s very responsive, but twitchy (see no end of threads about this in their forums).