Reducing additional latency in jackdmp async mode

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Reducing additional latency in jackdmp async mode

Stéphane Letz

In jackdmp  "async" mode (when the server does not wait for the graph  
end in a given cycle but use output buffer computed the previous  
cycle), there is up to one buffer more latency in the system.

On OSX (starting on Tiger) a property of the driver (called  
kAudioDevicePropertyIOCycleUsage) allows to setup "how much of the  
client portion of the IO cycle the process will use". Since the jack  
server async mode does a "constant in time" computation at each cycle  
(read input buffer, write output buffers from the previous cycle,  
activate the graph), one can safely use this  
kAudioDevicePropertyIOCycleUsage to a value < 1. The result is that  
the output buffer size is lowered internally in the driver and the  
overall latency can be reduced.

I guess a similar mechanism could be used in the ALSA driver. How can  
the output buffer size be lowered at the driver level to achieve the  
same effect?



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