Re: Suitability of Core Audio for Software Defined Radio?
Re: Suitability of Core Audio for Software Defined Radio?
- Subject: Re: Suitability of Core Audio for Software Defined Radio?
- From: Brian Willoughby <email@hidden>
- Date: Tue, 08 Mar 2011 00:13:11 -0800
On Mar 7, 2011, at 14:41, Rick Mann wrote:
I'm stepping into Software Defined Radio on the Mac, trying to
write a basic app. It occurs to me that Core Audio might be a nice
environment in which to architect an SDR app. But I'm not sure of
its suitability, having only looked at it and never really written
an audio processing unit.
To implement SDR, one needs to be able to process complex data
(real & imaginary components). I think Core Audio is fairly
flexible as to the structure of the samples in the pipeline, but I
wanted to touch base with the list and see if there'd be any
showstoppers preventing its use for this application.
The end result of SDR is audio data, or a stream of bytes (digital
data that was sent over the radio link).
I don't think that CoreAudio supports complex data, per se, but you
might be able to coax an AudioStreamBasicDescription into carrying
complex data. The problem is that no AudioUnits are going to expect
complex data, so direct support of complex data seems doubtful for
several reasons.
However, the SDR systems that I am aware of simply use "stereo" data
streams to carry the real & imaginary components. In that respect,
CoreAudio is easily able to handle any number of channels - certainly
as many as your interface provides.
My guess would be that while you might obtain complex data directly
from the audio input device, you'll probably want to convert to
normal audio fairly quickly in the signal chain. Then again, you
could easily put filters and other processing on the individual
channels, as long as the filters do not depend on complex input. Of
course, you could write your own AudioUnits which assume complex
input, and although CoreAudio would have no way to communicate the
complex data format to other AudioUnits in a graph, you would still
be able to patch data streams in various configurations.
Brian Willoughby
Sound Consulting
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