[LAU] jack2 vs. jack1/zita vs. jack2+zita-a2j, performance differences

[Jonathan E. Brickman]

Thought the below might be of interest to some.  The last is the best :-)  Hardware and clients identical, octo 4GHz, test load is one yoshimi with jack_keyboard driving by way of a passthrough mididings.


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Item one is vanilla distro jack2, run like this:


jack_control start
jack_control ds alsa
jack_control dps device hw:SB
jack_control dps rate 48000
jack_control dps nperiods 2
jack_control dps period 128
jack_control dps midi-driver seq
jack_control dps inchannels 2
jack_control dps outchannels 2
jack_control eps realtime true
jack_control eps realtime-priority 50
jack_control eps clock-source 1



The above is as low in reported latency I could go, 5.33ms, using every optimization I know of via the Arch wiki and realtimeconfigquickscan and other sources.  Running load-less, it gives me usage ranging 0.9 through 1.4%, usually hanging in at 1.3%.  With the test load, it tends to sit at 10% and rise with stress.  A few xruns every once in a while are inevitable, even when the test load is delivering only silence.  Nice tone quality.


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Item two is jack1-git, compiled with Zita libraries engaged, run like this:


nohup schedtool -R -p 50 -e /usr/bin/jackd -A SB -R -c h -X alsa_midi -d dummy -r 48000 -p 32 &


Reported latency is 2ms.  Load-less, usage rating is 1.3% through 29%, usually hanging in at 1.4% or so.  With the test load, it sits at 31.2% at silence.  No xruns.  But no actual sound came out :-)


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Item three is jack1-git, Zita libraries present but not used, run like this:
nohup schedtool -R -p 50 -e /usr/bin/jackd -R -c h -X alsa_midi -d dummy -r 48000 -p 32 &
nohup schedtool -R -p 50 -e /usr/local/bin/zita-j2a -d hw:SB


2ms reported latency.  Loadless usage is 20%.  With test load, 25-33% at silence.  No xruns.  Distorted sound.


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Item four is jack2 vanilla distro, run like this:


jack_control start
jack_control ds dummy
jack_control dps rate 48000
jack_control dps nperiods 2
jack_control dps period 32
jack_control dps inchannels 2
jack_control dps outchannels 2
jack_control eps realtime true
jack_control eps realtime-priority 50
jack_control eps clock-source 1

schedtool -R -p 50 -e /usr/bin/a2jmidid
schedtool -R -p 50 -e /usr/local/bin/zita-j2a -d hw:SB


2ms reported latency.  Loadless usage 3.8 to 4.3%.  With triple test load (three Yoshimis which is actually SOP for this rig), 4.5-5.5% at silence.  No xruns.  Wonderful sound, and no xruns with that triple load being pushed.


Will be starting rigorous testing at lower latencies soon, but I have an instrument which has to sing first :-)

Jonathan E. Brickman
Ponderworthy Music | jeb at ponderworthy.com | (785)233-9977 | http://ponderworthy.com




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