With Jack constant Dsp usage

Hi. I just noticed that I have a more constant dsp load with Jack than with Alsa. With Alsa the Dsp jumps sometimes from 55% to 100% and x-runs occur. With Jack I have a dsp utilization of about 50% and then it stays constant. What is the reason for this?

Jack uses Alsa underneath, so I would expect similar performance. However, perhaps your are not using the same audio settings for each, i.e. sample rate, frames per period, and periods per buffer. These settings determine the latency of your setup. The lower the latency the greater likelihood of x-runs. If you start Ardour you can see the audio settings in the Audio/Midi panel when you start a new session. Otherwise, x-runs can occur if you use a CPU-intensive plugin. Do the x-runs occur when you are doing the same actions in Ardour?

I have the same sample rate, frames per period and periods per buffer. Yes, the x-runs occur with the same actions. When I have the song on pause, the dsp usage is at 55%. As soon as I press play, the Dsp load shoots up to over 90% or 100% and then slowly drops down. With Jack, the Dsp remains stable at 50%

JACK reports average load, while Ardour/ALSA (and other Ardour internal backends) shows worst-case load (with a 2-3sec falloff).

The problem with JACK is that the average might be 50%, but in reality it is 10% and sometimes 90%. That is sadly useless, because with audio the worst-case is what matters.

Recent Ardour (since 6.9) has Menu > Window > Performance Meters. That shows worst-case DSP load regardless of the backend in use.

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Uh… Ok, i understand, that makes sense. Thanks Robin for the info!

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