Re: Curious happening with CAPlayThough
Re: Curious happening with CAPlayThough
- Subject: Re: Curious happening with CAPlayThough
- From: Jeff Moore <email@hidden>
- Date: Wed, 07 Jan 2009 18:37:48 -0800
On Jan 7, 2009, at 6:09 PM, Neil Clayton wrote:
Thanks Jeff,
To be more specific, I can click it once and hear this "echo" at the
end of the audio being played. I'm certain it's not because I'm
clicking many times (I'm not clicking wildly, just clicking numerous
times, with delays in between each to hear the outcome).
That falls within the description of one of the hard-to-reproduce bugs
I was referring to.
I'd believe it were something to do with the sound server if I heard
the issue with all three tools that I tried. The fact that it works
with both GarageBand and LineIn makes me suspect something is
different about the code. That's kinda why I asked - not to "blame"
CAPlayThrough in any way but to try to learn what was causing it.
Out of interest, it occurs with afplay as well. Not as obvious, but
it certainly happens.
Here's a recording of the output:
http://dl.getdropbox.com/u/421935/Sample of Audio Blips
If I understand what you are saying, you produced this file thusly:
1) set SoundFlower as the default output device.
2) set up CAPlayThrough so that it is echoing the SoundFlower input to
the built-in output
3) use afplay to play files out of /System/Library/Sounds meaning that
each sound I hear in the recording is played via an invocation of
afplay.
Is this correct?
If so, this technique would nicely cut the System Sound Server out of
the picture and absolve it of any guilt. The resulting glitches would
then be either in SoundFlower when it is echoing it's output back to
it's input or in CAPlayThrough when it is echoing the SoundFlower
input to the built-in output.
So, the next thing to do would be to isolate the problem further by
recording the input from directly from SoundFlower while you are
testing. If the glitches are in the resulting recording, then you know
that the problem is coming from SoundFlower. If the glitches are not
in the recording, then the problem is with CAPlayThrough.
On 8/01/2009, at 2:13 PM, Jeff Moore wrote:
I believe that you are probably just hearing the results of either
the System Sound Server handles re-triggering a sound while the
sound is already playing. Or it's just some kind of playback bug in
the SSS (possibly one that's been around for a while but very hard
to reproduce normally).
At any rate, it seems unlikely to be a bug in CAPlayThrough though.
I'd verify this by making sure that just playing audio to this
pipeline with a tool like afplay never has any artifacts.
It is definitely worth writing this up as a bug for us to look at
though.
On Jan 7, 2009, at 4:19 PM, Neil Clayton wrote:
I'm seeing some odd behavior that I'd like to clarify please.
I install Soundflower 2ch, and playthru from that to the built in
line-output. I setup the SF2ch device to be the default output.
I then go to system preferences Sound page, and repeatedly click
on the "Ping" sound (to hear it).
What I hear is that sometimes, it's broken up. As though the
last part of the sample is played again briefly.
Curiously, if I play iTunes to the SF2ch (and through
CAPlaythrough, to the default output) it's absolutely fine.
I'm pretty sure it's not the SF driver itself (but not 100%, I've
not verified the code at all), because it works find if I use
GarageBand for the same task (the playthru part). It also works
fine with LineIn (a similar util, free, from Rogue Amoeba).
So my question is; is this something to do with the way that the
AU is setup? Or to do with flags passed in during the
AudioUnitRender? Or something else entirely?
--
Jeff Moore
Core Audio
Apple
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Neil Clayton
email@hidden
--
Jeff Moore
Core Audio
Apple
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