[vorbis-dev] Observations about the floating point data in vorbisfile

Michael Smith msmith at labyrinth.net.au
Sun Feb 2 19:57:26 PST 2003

Tomas Ogren <stric at ing.umu.se> said:

> Hello.
> I noticed that when reading data with ov_read_float(), you can get
> values outside [-1..1] when the stream is encoded at lower quality, but
> with higher quality, the values trim down to inside [-1..1].
> Looking at the plot from -q10, the data from ov_read_float seems
> clipped.

This is correct. As a lossy codec, vorbis does not guarantee that the output
will be the same as the input (obviously) - and part of that is that the
approximations may produce out of range output. ov_read() performs clipping,
as you noted, in order to deal with this. If you use ov_read_float(), it's up
to you to deal with the values produced appropriately.

This problem generally only happens (at least in ways that matter - i.e. could
be audible) with peak-to-peak inputs, which are a bad idea anyway. 


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