[opus] OPUS vs MP3

[Jean-Marc Valin]

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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