[linux-audio-dev] [OT] marketing hype

Paul Davis paul at linuxaudiosystems.com
Fri Jun 11 12:37:09 UTC 2004


>moreover, iirc, the design of jackd makes no consideration for
>'live' routing changes. At least on my system, changing the graph
>results in an xrun.

last time i plug an analog signal into an analog patchbay, there was a
click. 

you cannot modify the graph in JACK while the graph is being used to
process audio. you do not know how long the graph modification will
take if you try to do it (for example) right after you're done with
one process cycle. the only sure way to do this is to use lock free
parallel programming techniques. this is still a highly experimental
area of computer science, and i have yet to see more than a glimmer of
a technique that would actually work in a complex real time system
like JACK. the designs that exist to date tend to work better (if at
all) in situations where the software objects do not have much
"weight" to them. the JACK graph describes quite a resource-heavy
state (shared memory, device driver handles, processes, etc. etc.),
and making a copy of it so that you modify it and then switch pointers
is not a practical approach.

the fact that some systems can do live repatching without xruns is
either good luck, or a function of them using very lightweight objects
that don't directly reference expensive resources.

--p





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