[OT] [vorbis] Should Speex VBR Introduce Distortion?

[Tyler Knott]

J C Fitzgerald wrote:

>Hi All,
>
>I've run into a small hiccup in encoding my audios with Speex.  When I
>encode audience laughter and applause with 'speexenc' (version 1.0.1),
>the result is quite acceptable... until I enable VBR.  Then it distorts
>horribly.
>
>My understanding of VBR is that it frees the encoder to vary the number
>of bits emitted to better maintain the quality requested, and so I would
>have expected, if there were to be distortion, that it would have shown
>itself with VBR turned off.
>
>I thought that VBR turning on VAD might be persuading the encoder to
>interpret the sound as background noise, but experiments with VAD in CBR
>mode seem to my ear to add only a very small amount of distortion over
>non-VAD CBR mode and certainly nothing like the VBR level.
>
>I don't believe it is the playback that is at fault as it handles the
>CBR mode Speex file, the same source Vorbis encoded and the original
>RIFF files just fine.  It is possible that Speex requires such a high
>bit rate to represent the audio at these times that it swamps the player,
>but I would not have expected it to be much higher than what would have
>been required in CBR mode.
>
>So, am I looking at an encoding artifact here, or is there a less naive
>answer?
>  
>
Speex isnt' really meant to encode laughter & clapping so it isn't tuned 
for l&c which is why it sounds so bad in VBR mode(it thinks it can use 
less bits to represent the sound acuratly than it needs).  VAD and DTX 
shouldn't really matter.  If you need to use VBR then try a higher 
quality setting.

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