Re: Smallest buffer duration in AudioQueue
Re: Smallest buffer duration in AudioQueue
- Subject: Re: Smallest buffer duration in AudioQueue
- From: tahome izwah <email@hidden>
- Date: Mon, 04 Jul 2011 08:12:54 +0200
Last time I checked the iMac always did EQ if you were using the
built-in speakers, because it would otherwise sound like crap (you can
hear the difference by comparing the startup chime to iTunes
playback).
As I read it you were talking about AudioQueue, not CoreAudio in
general. I'm sure that CA can provide lower latency, but AudioQueue is
a high level API with lots of stuff going on behind the scenes so it's
possible you can't use it for your purpose.
HTH
--th
2011/7/2 Aristotel Digenis <email@hidden>:
> Hi,
> Well I am assuming that there is no sample rate conversion as I am running
> it at the same sample rate as the card is set to. The data is in PCM so
> there isn't any conversion (other than possible from float to whatever the
> sound card expects natively), and there is no EQ or anything like that. That
> just leaves the overhead of the scheduling, but surely that can't be that
> high. Other DAW's can go down to 5.3ms buffers and lower without a problem.
> For example Plogue's Bidule (http://www.plogue.com/?page_id=56), which is
> based on PortAudio allows me to set the buffer size right down to a
> ridiculously small 32 sample buffer (on a 48000Hz sample rate), and that is
> with running lots of other DSP on it. So here I am in CoreAudio not able to
> get to less than 6000 sample buffers. What am I missing?
> Thanks
>
>> Date: Sat, 2 Jul 2011 13:49:58 +0200
>> From: email@hidden
>> To: email@hidden
>> Subject: Re: Smallest buffer duration in AudioQueue
>>
>> How do you know how much overhead there is per buffer (data
>> conversion, sample rate conversion, loop overhead, EQ, scheduling)? It
>> could simply be that the accumulated overhead gets too large when you
>> reduce buffer size too much. This need not have anything to do with
>> the code that generates your sine wave...
>>
>> --th
>>
>> 2011/7/2 Aristotel Digenis <email@hidden>:
>> > Hello everyone,
>> > I have a basic AudioQueue setup with a callback that generates a sine
>> > wave.
>> > The problem is the when the buffers are under 125ms in duration, I get
>> > clicks. On a 48000Hz with 2 buffers each of 6000 frames long, it works
>> > fine.
>> > As soon as I drop the frames per buffer down to 5999, I get
>> > discontinuities.
>> > Increasing the number of buffer doesn't change things and the callback
>> > is
>> > very simple, just generating a sine wave.. so it can't be that it isn't
>> > generating the signal in-time.
>> > This is all on an iMac with OS X 10.6 if that is of any help. Has
>> > anybody
>> > managed to get AudioQueue to work with less than 125ms latency/buffers?
>> > If
>> > so, how?
>> > Thanks
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