Re: WaveIn notification methods

From: Grant Schenck (schenckg_at_optonline.net)
Date: 10/15/04 

Date: Fri, 15 Oct 2004 17:00:08 -0400

Chris,

As always, thanks for your advice and knowledge. This is good stuff
and matches my understanding.

Earlier I had issues with the wave in events getting stuck somewhere
when I moved other windows on my desktop. I decided to revisit this
and have a case working with MS on it. I'm not optimistic in terms of
getting to the bottom of it.

I agree on polling vs. other mechanisms. Specifically in my wait I
tried using a 5 ms timeout and checking the buffers whether the event
popped or I fell out of the wait due to the time out. That didn't
help and based on that I can say the issue is that the event isn't
popping because the driver is not marking the buffers done. Why the
driver stops marking buffers done is beyond me.

Thanks, Grant

"Chris P. [MVP]" <msdn@chrisnet.net> wrote in message
news:#IP7elrsEHA.3972@TK2MSFTNGP15.phx.gbl...
> Grant Schenck wrote:
>
> > "Are you using waveInOpen( )? If so, have you tried with
different
> > callback modes, such as CALLBACK_FUNCTION, or CALLBACK_THREAD?"
> >
> > I looked at the docs and CALLBACK_THREAD seems to involve a
windows
> > message. Searching on goggle the opinions I saw seemed to
recommend
> > against using it. What to you folks think? Is there any point in
> > replacing CALLBACK_EVENT with CALLBACK_THREAD if I'm trying to
achieve
> > high performance audio?
> >
> > What about CALLBACK_FUNCTION? I assume that is better then
> > CALLBACK_THREAD but is there any reason to think it would be
better
> > then CALLBACK_EVENT?
>
> Many many many many years back I was having the same dilemma as you
trying
> to decide what to use. So many choices! I wrote a test program
that
> implemented all the different methods to see what would work best.
Here
> were my discoveries:
>
> CALLBACK_WINDOW - Seemed ok at first, but fell apart when there were
many
> window messages flying about. Perhaps the simplest method to
implement.
>
> CALLBACK_FUNCTION - Essentially useless because you can't do any
audio
> handing in the callback. You're choices are to signal an event or
post a
> window message, why created this method beats the **** out of me.
>
> CALLBACK_THREAD - Didn't work much better than CALLBACK_WINDOW.
Makes the
> code a little cleaner and allows you to elevate the thread priority
of the
> worker thread for a slight performance improvement.
>
> CALLBACK_EVENT - Worked well on the NT systems. Requires a
dedicated worker
> thread to operate at full potential. The worker thread must be
using
> WaitOnSingleObject() or WaitOnMultipleObjects(), using any function
call
> that generated or processed messages such as
MsgWaitForMultipleObjects()
> seemed to have a negative impact on performance.
>
> Now the method you probably didn't think about - CALLBACK_NULL. Yes
you
> might be suprised to find out that the lowest latency solution in
many cases
> is not to use any callback method at all but rather to poll the
buffer
> flags. Polling at a rate of 100 to 200 times a second can get you
latency
> in the 20ms range at the expense of a little CPU power. It really
doesn't
> use much if you throw a Sleep(5) into the loop. Obviously this
requires a
> dedicated thread and ideally the thread should be set to
> THREAD_PRIORITY_TIME_CRITICAL. Make sure there is absolutely no
code in
> this high priority thread that can block or you will bring the
system to
> it's knees. That means no disk I/O, network etc.
>
> Which one to use for lowest latency? CALLBACK_EVENT is typically
the best,
> and with special audio drivers can achieve latency down in the 5ms
range.
> Second best, if CALLBACK_EVENT doesn't work out is polling. It's
not really
> worth trying to get the latency too low with WaveIn/Out unless the
> manufacturer of the audio device has supplied special drivers as
your going
> to be hit by the kmixer 30ms delay anyway.
>
> -Chris
>
>

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