Re: [linux-audio-dev] audio project

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Subject: Re: [linux-audio-dev] audio project
From: Paul Davis (pbd_AT_op.net)
Date: Thu May 09 2002 - 02:35:46 EEST


>> A quick question, do I need to load a Jack server independently of my
>> actual software?
>
>yes. (there was talk of "including" jack into applications via a
>jacklib, so that your program would take the role of a jack server if
>none can be found at startup, but that's probably complicating things a
>bit...)

we haven't done that yet. we might still. so yes, you start JACK and
leave it running. if it helps to convince you, both Kai and myself
have had JACK servers running for several days non-stop while running
experimental, segfaulting, unpredictable, dynamic and demanding
clients that start and stop dozens or even hundreds of times.

>> If so, does this have an increased processing overhead?
>
>i think that's negligible for the task you are doing. i may be wrong,
>though.

almost no overhead whatsoever (the amount starts at about 50usecs on a
PII-450, and is variable depending on how much memory your process()
callback touches).

please understand that what you have described is exactly what JACK
was designed for. instead of you wasting your time implementing audio
i/o, and never being able to share data with other applications as
sources or destinations, just use JACK and you can focus on the core
"DSP" part of whatever your application does. then someday, rather
than use your app to process data coming from the soundcard, it can
handle data coming from a drum machine or softsynth without changing
anything at all :)

as for docs: yes, what we have right now is mostly a reference. but we
hope that the example clients (simple_client.c being the simplest)
explain things fairly well. the basic idea is that you register with
JACK, then supply a callback function that will be executed whenever
there is work to do. you have no control of or over the audio
interface, and indeed, there may not even be an audio interface. your
application doesn't care about stuff like this anymore. this is the
same as Mac OS X's CoreAudio API and several other excellent APIs.

--p


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