[opus] OPUS vs MP3

[Marc Lavallée]

Can such normally inaudible processing of the audio signal affect
Ambisonics reproduction?

--
Marc

Le Lundi 30 Oct 2017 22:08:41 -0400
Jean-Marc Valin <jmvalin at jmvalin.ca> a écrit:

> Just to be clear, my goal here wasn't to make fun of anyone, but to
> drive the point that spectrograms should *never* be used to
> demonstrate quality. The only case where they can sometimes be useful
> is for diagnostic purposes. If you hear something and you're not sure
> what you're hearing exactly, then sometimes a spectrogram can help
> you figure out what it is. That's pretty much it. If you can't hear
> any artefact, who cares what the spectrogram looks like?
> 
> Also, looking at the difference signal (either as a spectrogram or as
> actual audio) is particularly dangerous. There are many things you can
> do to an audio signal that are completely inaudible and yet will cause
> quite large differences (e.g. flip the sign or delay by X samples, but
> there's many more).
> 
> Cheers,
> 
> 	Jean-Marc
> 
> On 10/30/2017 08:16 PM, Orestes Zoupanos wrote:
> > Jean-Mark sarkasm.
> > 
> > Jean-Markasm.
> > 
> > (Bonus points for providing an actual noisy WAV! ^_^)
> > 
> > On 30/10/2017 20:28, Jean-Marc Valin wrote:  
> >> Hi,
> >>
> >> Before I comment on the graphics you posted to visualize the
> >> difference between two audio signals, I'd like to ask for your
> >> help in evaluating my JPEG encoder. I've encoded an image with
> >> JPEG and then computed the difference with the original. I then
> >> converted the difference to sound. You can listen to the image
> >> difference on this clip: https://jmvalin.ca/misc_stuff/diff.wav
> >>
> >> Can you hear how good the visual quality is? Do you think it could
> >> be improved to make JPEG sound better? Personally, I think JPEG
> >> could do better on my subwoofer.
> >>
> >> Cheers,
> >>
> >> 	Jean-Marc
> >>
> >> On 10/18/2017 07:08 PM, encrupted anonymous wrote:  
> >>> Good morning.
> >>>
> >>> I've ran a test against MP3 format.
> >>>
> >>> Code: (first convert tested audio file to 16 bit 48khz with
> >>> sox.exe if needed)
> >>> lame.exe -b 320 48khzfilein.wav -o fileout.mp3
> >>> lame --decode fileout.mp3 -o fileout.mp3.wav
> >>> opusenc.exe --bitrate 320 48khzfilein.wav fileout.opus
> >>> opusdec.exe fileout.opus fileout.opus.wav
> >>> wavdiff.exe 48khzfilein.wav fileout.mp3.wav -diff
> >>> fileout.mp3.delta.wav wavdiff.exe 48khzfilein.wav
> >>> fileout.opus.wav -diff fileout.opus.delta.wav
> >>>
> >>> Results: (compare two deltas with spek.exe - i've attached
> >>> graphic file from my test)
> >>> MP3 much better at 0-4 kHz, Opus little better at 12-20 kHz.
> >>> Plus I think 0-4 kHz is more important than 12-20.
> >>>
> >>> Current Opus 1.2.1 is the best at 32 kbit/s for music.
> >>> But if you input 44100 Hz audio and give 96-512 kbit/s, Opus
> >>> pretty badly spends that much bitrate because of frame rate
> >>> conversion.
> >>>
> >>> That's all I wanted to say for now, good evening.
> >>>
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> >>>
> >>>
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