Built-in audio devices unexpected behavior
Built-in audio devices unexpected behavior
- Subject: Built-in audio devices unexpected behavior
- From: Mikael Hakman <email@hidden>
- Date: Tue, 19 Aug 2008 14:23:52 +0200
While performing some tests using
built-in audio devices I observed following behavior not consistent
with my expectations.
Whenever my application sets
virtual format on either input or output device to standard Float32
PCM then physical format changes to 16-bits even if I set it to
24-bits in AMS.
According to HALLab and to
returned kAudioDevicePropertyLatency/kAudioStreamPropertyLatency
properties, latency of these devices is 30 samples. Connecting
output to input, outputting a single pulse, and measuring the number
of samples until the pulse appears on input yields a total latency
of about 900 samples when using 128 sample buffer sizes. I would
expect total latency of 128 + 30 + 30 = 188 samples.
Whenever optical input signal
ceases then input device changes its input stream from digital to
line-in despite optical connector still being physically connected.
I would expect reported input stream still being digital but with no
channels in it when there is no valid digital signal. Output device
does it right – when optical jack is connected then the stream is
digital, when analog jack is connected then the stream is line-out. Could you please comment on these
observations. Thanks/Mikael
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