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kAudioFormatFlagIsFloat sample range
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kAudioFormatFlagIsFloat sample range


  • Subject: kAudioFormatFlagIsFloat sample range
  • From: "Stephen F. Booth" <email@hidden>
  • Date: Sat, 11 Sep 2010 20:49:56 -0700

Hello all,

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.

A representative file looks like:

File data format:
AudioStreamBasicDescription:  2 ch,  44100 Hz, 'aac ' (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame

Client format:
AudioStreamBasicDescription:  2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved

After each call to ExtAudioFileRead I scan for the min/max sample values, and here is an example of what I'm seeing:

Max sample value: 1.011417
Min sample value: -1.063289
Min sample value: -1.003544
Min sample value: -1.058746
Min sample value: -1.077708
Max sample value: 1.046287

Is this to be expected?

Thanks,
Stephen
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