Re: How do you get the native bit-depth of the input device?
Re: How do you get the native bit-depth of the input device?
- Subject: Re: How do you get the native bit-depth of the input device?
- From: Jeff Moore <email@hidden>
- Date: Mon, 13 Aug 2007 11:42:04 -0700
That is exactly correct.
Good luck!
On Aug 10, 2007, at 7:21 PM, Dave Fernandes wrote:
OK. I think the part I was missing was the mapping of channels to
streams. From what you have said, I gather that:
Each channel has exactly one physical stream associated with it.
Each stream, however, may handle multiple channels using the same
ASBD.
Is that correct?
On Aug 10, 2007, at 9:19 PM, Jeff Moore wrote:
All the info you need is contained in the various AudioStream
properties that pertain to the format. You get a list of what
formats are available for each stream as well as what format is
currently selected.
As for which stream the user is using, that is actually already
known to you since you have to know that in order to process the
incoming audio data. If you are trying to capture stereo data from
a multi-channel device, you'll need to put some UI in to allow the
user to tell you which two channels to use (you can also use the
default stereo pair property). Since you know which two channels
(or whatever number) you are using, it is a simple matter to
identify the stream those channels belong to.
BTW, you might want to look over the HALLab sample app in our SDK.
While it probably won't help you out with your AUHAL code, it is a
good app to use to get a feel for how audio devices are represented
in the system.
On Aug 10, 2007, at 5:32 PM, Dave Fernandes wrote:
So if my user plugs in a complex device with multiple input
streams, how can they tell me which one(s) they are using? I need
to get and set bit-depths and sample rates for the correct stream.
Is it possible to support multi-stream devices without specs from
the device manufacturer?
On Aug 10, 2007, at 8:06 PM, Jeff Moore wrote:
On Aug 10, 2007, at 4:49 PM, Dave Fernandes wrote:
Thanks! It took me a while to figure out how to get this format
info, but I think it is working. I'm using the "master channel"
of the AudioDevice to get the AudioStream to get the format. Is
this correct?
You're close. Format info in the HAL is handled differently than
it is in AUHAL. Each audio device has some number of streams and
each stream has it's own format. Thus, the format of the audio
device is actually a vector of ASBDs, one for each stream. So, to
get the format of the device, you'd do the following (in pseudo
code):
Get the list of streams for the device
For each stream do
Get the physical format of the stream
By just getting the format of the first stream, you are only
getting a partial picture of the format of the device. For
devices that have only one stream in a given direction (like the
built-in hardware), this will be fine. But for more complex
hardware, it will leave you with just part of the info.
I can't find any documentation on what exactly a master channel
is.
This is covered somewhat in <CoreAudio/AudioHardware.h>. But the
short answer is that the HAL always numbers channels in streams
starting with number 1. Number 0 is reserved for the "master"
channel which is useful for controls or properties that apply to
the entire scope or object involved.
In the case of the stream format stuff, getting the various
device related format properties on the master channel gets you
the information about the first stream of the device in the given
direction.
Dave
On Aug 6, 2007, at 2:57 PM, William Stewart wrote:
In AudioHardware.h there are format descriptor properties for
the virtual and physical formats of the device. The virtual
format is normally the canonical Float32. The physical format
is whatever the device is using.
On 02/08/2007, at 2:24 PM, Dave Fernandes wrote:
The AudioOutputUnit nicely provides a stream of Float32
samples. But I would like to choose the bit-depth of the file
I am recording to based on the precision of the input device.
So how can I determine this precision? The
--
Jeff Moore
Core Audio
Apple
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Core Audio
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