Re: [LAU] (Ardour) How to get rid of delay when recording ?

On Sat, Feb 13, 2016 at 10:23 PM, jonetsu(a)teksavvy.com &lt;jonetsu(a)teksavvy.com&gt; wrote: See the "Running RtIRQ" section of the real-time tuning page, and you'll see how to set the priority IRQ for the soundcard (summarized below): http://openavproductions.com/real-time-latency-tuning/ Summary: 1) Get PID of task that services the soundcard interrupt: ps -eo pid,rtprio,comm --sort -rtprio | head -n 30 2) Change the priority of that task: chrt -f -p 84 <PID of IRQ handler> "Good" depends on use case ;) The "real" measure of latency is much more representative than the number of frames in a buffer. Samplerate, number of buffers, and buffer-size are the 3 factors for latency. There is also some latency in the ADC and DAC converters (no flame-discussions indented :) Its easy to measure the total round-trip delay: jack_iodelay For full info, read here: http://apps.linuxaudio.org/wiki/jack_latency_tests For testing, just run jack_iodelay, and then connect a loopback cable to the soundcard (aka, output -> input). Connect jack_iodelay to the soundcard's hardware input/output ports you just patched, and jack_iodelay will tell you a very precise amount of latency. Example screenshot: http://openavproductions.com/realtime_latency.png I run jackd with -p 48 -n1 -r48000, causing a theory of 1ms input, and 1ms output. Note: -n1 makes no sense, see that jackd/alsa corrects this to -n2, because one input and one output buffer is needed. So in theory, we have 2 * 48 / 48000. round trip latency: 2ms. jack_iodelay actually measures 6.629. Why? ADC / DAC conversion delay. The soundcard in use here is an "Art USB Dual Pre", retails for < 100 euro. These converters will probably not be particularly low-latency ones. For curiosities sake, would you mind measuing the round-trip delay? (Assuming you have a loopback cable available and time :) I think you might be surprised... because I always am that its actually worse than we think, because I usually look at the software "theory" latency, instead of actually measuring :D Cheers, -Harry -- http://www.openavproductions.com