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Re: FLLR (compression ?) in AIFF file
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Re: FLLR (compression ?) in AIFF file

On Aug 6, 2008, at 10:44 AM, Francois Baronnet wrote:

2008/8/6 Richard Dobson <email@hidden>:
Stephen Davis wrote:

The FLLR chunk is added by the AudioFile code to align the data chunk on a
4K page boundary for optimized I/O during playback.

The AIFF specification says to ignore chunks you don't recognize and skip
over them. This is such a chunk. :-)

As for the NONE chunk, it is not a separate chunk but is found in the
"compressionType" field of the COMM chunk.


Only in AIFC files (the COMM chunk is larger there with extra fields). AIFF
does not support compression (or 32bit floats). But the recommendation is
that AIFC supercedes AIFF, so should be used for everything, these days. 

Oops, Richard is correct.


Ok, thanks. As I'm the recorder of the sound and then there is only me
to analyse it (then the sound file is deleted), I thing I can use
uncompressed AIFF, no?

Please correct me if I go wrong, but if I move to the SSND chunk, I
should find very closed to it the "sound data", shouldn't I?
And these data must be of type float, from -1.000 to 1.000, right? If
it's true, then I don't understand why I'm getting stange numbers
(xxx.xx E-41 for example).

Here is a screenshot of my file opened with some hexadecimal editor.
My app is reading from 00 22 00 00 until the end of file.
http://cpcstats.free.fr/upload/files/1218044603_Image_1.png

May be it's not float? May be the offset isn't good? I tried many
combinations but I can't get one "good" float value...


Your original email said your file audio format was:

Here are my settings for AIFF file:

aqData.mDataFormat.mFormatID = kAudioFormatLinearPCM;
aqData.mDataFormat.mSampleRate = 44100.0;
aqData.mDataFormat.mChannelsPerFrame = 2;
aqData.mDataFormat.mBitsPerChannel = 16;
aqData.mDataFormat.mBytesPerPacket =
aqData.mDataFormat.mBytesPerFrame =
aqData.mDataFormat.mChannelsPerFrame * sizeof (SInt16);

aqData.mDataFormat.mFramesPerPacket = 1;
AudioFileTypeID fileType = kAudioFileAIFFType;

aqData.mDataFormat.mFormatFlags =
	kLinearPCMFormatFlagIsBigEndian
	| kLinearPCMFormatFlagIsSignedInteger
	| kLinearPCMFormatFlagIsPacked;

You're setting the data to 16-bit linear integer PCM. Why are you expecting to read 32-bit floats?

stephen

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References: 


 >FLLR (compression ?) in AIFF file (From: "Francois Baronnet" <email@hidden>)


 >Re: FLLR (compression ?) in AIFF file (From: Stephen Davis <email@hidden>)


 >Re: FLLR (compression ?) in AIFF file (From: Richard Dobson <email@hidden>)


 >Re: FLLR (compression ?) in AIFF file (From: "Francois Baronnet" <email@hidden>)























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