Re: USB Audio streaming start
Re: USB Audio streaming start
- Subject: Re: USB Audio streaming start
- From: Daniel Mack <email@hidden>
- Date: Thu, 20 Oct 2011 13:15:22 +0200
On 19.10.11 22:00, Vyacheslav Matyushin wrote:
> Thank you very much for this idea.
>
> Make your IOAudioEngine buffer bigger so it wraps around once or twice a
> second only.
>
>
> Why should IOAudioEngine buffer be of that size?
>
> The only thing I've found which is influenced by that
> buffer size is HAL buffer size which can be
> up to 3/8 of IOAudioEngine buffer size.
Exactly. While it is a good thing to get low latencies for pro audio
applications, other use cases (such as playing audio with iTunes) does
not benefit from this feature as it has to wake up more frequently to
provide new content which will add to the system load.
Also, it is not necessary. Buffers are organized in rings, not as
flip-pages like ASIO does it.
> HAL buffer size is in latency formula
> (output sample offset + output sample latency
> + output buffer size + all the same for input)
> so shouldn't increasing IOAudioEngine buffer size also increase the latency?
No, it doesn't. The latency is defined by the time difference of the
actual position of the IOAudioEngine and the time at which CoreAudio
writes new sample material. CoreAudio will approximate to this position
with math based on the time stamps the driver provides by calling
takeTimeStamp(). It is hence crucial to provide very accurate timing
information.
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