[opus] Audio Mode vs. VoIP Mode

Jean-Marc Valin jmvalin at jmvalin.ca
Thu May 2 14:09:54 PDT 2013

On 02/05/13 11:09 AM, van Bijleveld Christian (ST-CO/ENG1.3) wrote:
> However I observe that when decompressing the compressed audio (using
> the same decoder for both audio and voip), the decompressed audio
> version resembles the original audio much better compared to the voip
> version. See the attached picture:
> It looks as if the voip version (dotted green) has some kind of
> offset, and the audio version (dotted red) is much closer to the
> original audio. Is there an explanation for this? 

Well, the attached picture got stripped along the way (zip file
filtering), so it's not clear what exactly is the difference. I would
say however that what you may be observing is the effect of the 50-Hz
high-pass filter that is applied only in voip mode. Keep in mind that in
the end what counts is the sound quality, not how nice it looks on a plot.

> Does the decoder
> also need to be configured as either audio or speech?

No, that's an encoder-only property.


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