Re: kAudioFormatFlagIsFloat sample range
Re: kAudioFormatFlagIsFloat sample range
- Subject: Re: kAudioFormatFlagIsFloat sample range
- From: "Stephen F. Booth" <email@hidden>
- Date: Sun, 12 Sep 2010 17:01:15 -0700
On Sun, Sep 12, 2010 at 12:09 AM, Brian Willoughby
<email@hidden> wrote:
On Sep 11, 2010, at 20:49, Stephen F. Booth wrote:
If kAudioFormatFlagIsFloat is set as part of an ExtAudioFile's client format, should the returned samples be in the range [-1, 1)? I've always worked under this assumption but I can't find anything explicit in the documentation. I've recently observed samples being returned from AAC files with values >= 1 (and < -1), which is causing clipping on one of my devices. It isn't difficult to perform hard limiting, but this is something I hadn't noticed before.
In my testing the Core Audio drivers do hard clip before data is sent if one is performing mixable IO. In my particular case I am performing non-mixable IO in the device's native format (24 bit LE signed integer) so the drivers are passing my buffers to the DAC unmodified. I didn't verify that the output from ExtAudioFileRead was in the correct range, so I was sending samples > 0x7fffff to the device. Some devices handle this with no audible artifacts, but some don't. For now as a temporary solution I am just clipping the ExtAudioFile return data using vDSP_vclip which solves the problem.
Stephen
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