Re: vDSP and iOS render callback
Re: vDSP and iOS render callback
- Subject: Re: vDSP and iOS render callback
- From: Brian Willoughby <email@hidden>
- Date: Tue, 24 Apr 2012 20:23:55 -0700
On Apr 24, 2012, at 18:25, Paul Davis wrote:
On Mon, Apr 23, 2012 at 4:16 PM, Kevin Dixon
<email@hidden> wrote:
Maybe I'm missing something, I was looking at this question stack
overflow (http://stackoverflow.com/questions/3398753/using-the-
apple-fft-and-accelerate-framework/3534926#3534926).
I was under the impression that the render callback supplied sample
data in 8.24 fixed format, yet I don't see any sort of type
conversion
going on in the example autocorrelation implementation when they call
the FFT.
Can anyone shed some light on this?
this is wrong. CoreAudio (like most audio SDKs) uses 32 bit floating
point as its only "native" data type. this absolutely includes the
render callback for an audio unit. unless iOS is totally different, in
which case forgive my emphasis.
Hey, Paul, the second thing you said is true: iOS is totally different.
CoreAudio for OSX does default to Float32 unless the code
specifically requests otherwise.
CoreAudio for iOS defaults to Q8.24, a fixed-point format that is
more efficient on the older ARM processors without fast float
support. In that world, I/O devices are 16-bit integer, and DSP is
run at 8.24 for speed.
The confusing thing is that the ARM chips are now getting to where
they support float as well as int, and so CoreAudio/iOS is moving
towards Float32.
Brian Willoughby
Sound Consulting
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