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

Segher Boessenkool segher at koffie.nl
Mon Feb 3 19:05:20 PST 2003

Michael Smith wrote:

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

Not all lossy codecs have overshoot.  It would be really great
if Vorbis could deal with this (yes, I know it's a hard problem).

> 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. 

Why are full-range inputs a bad idea?


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