On Wed, 27 Dec 2017, Manuel Haible wrote:
I assume: for high samplerates + many tracks + many fx + very small buffer size + ultra low latency singlecore performance is equally important as the number of cores?
Any one track with all its effects and buses it feeds must be in the same thread. That is, any audio operation that requires another's result to begin it's own processing must be run by the same thread. So yes, single core performance is important. For example, a guiter effects chain would be run as a single thread for audio (the GUI would be separate and probably of low priority) on one core.
That may be part of the problem with multi-core effects that sound better with multi-core use turned off. An effect is generally a serial chain of audio processes that should not be split up.
Secondary cores that borrow resources from another core like hyperthreading, may cause trouble for very low latency use. In the days of the single core P4, I found that with HT enabled I had the odd xrun with jack set 64/2, but with HT off I could get latency of 16/2 with no xruns using an ice1712 interface. I have not tested things on newer i3/7 cpus as I have side stepped the whole issue by using a 4 core i5.
CPU speed still affects things though. Anything that changes the cpu speed seems to affect audio. I have had better results forcing a cpu to only 800Mhz than allowing that same cpu to run at 1.6Ghz with speed changes. My i5 runs up to 3.2Ghz and just putting it into performance mode helps but "Boost" can cause xruns too I have found. I think I could set performance to 3.4ghz (effectively over clocking) and get things to work as the temperature stays within limits even with all 4 cores at 100% (building Ardour takes 15 minutes or so and makes quite a good cpu "burn" test) and audio can not run at 100% anyway. But I have not tried that.
-- Len Ovens www.ovenwerks.net
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