Re: Getting PCM data from MP3/AAC/ALAC File
Re: Getting PCM data from MP3/AAC/ALAC File
- Subject: Re: Getting PCM data from MP3/AAC/ALAC File
- From: Brian Willoughby <email@hidden>
- Date: Sat, 20 Dec 2008 20:03:38 -0800
The iPhone is quite the newcomer to the CoreAudio family. CoreAudio
has been around for almost a decade, I think, and it has been 32-bit
Linear PCM float during all of that time. The iPhone is probably the
first OSX platform which cannot support high MIPS rates with 32-bit
floats, so the recent change to CoreAudio to have an additional
platform-specific default of 8.24 integers is for performance
reasons. AudioUnits are also quite limited with the current iPhone
system.
If you're not working on the iPhone, then William's comments are dead-
on.
Brian Willoughby
Sound Consulting
On Dec 20, 2008, at 08:22, Hamish Allan wrote:
On Sat, Dec 20, 2008 at 3:08 PM, William Bates
<email@hidden> wrote:
For better or worse, the designers of Core Audio picked floats as the
"natural" representation.
That doesn't seem to be the case on the iPhone. From "Core Audio
Overview":
"The canonical formats in CoreAudio are as follows:
- iPhone OS input and output: Linear PCM with 16-bit integer samples
- iPhone OS audio units and other audio processing: Noninterleaved
linear PCM with 8.24-bit fixed-point samples
- Mac OS X input and output: Linear PCM with 32-bit floating point
samples
- Mac OS X audio units and other audio processing: Noninterleaved
linear PCM with 32-bit floating point samples"
H
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