[opus] Antw: Re: OPUS vs MP3
Ulrich.Windl at rz.uni-regensburg.de
Thu Nov 2 08:41:35 UTC 2017
>>> Jean-Marc Valin <jmvalin at jmvalin.ca> schrieb am 01.11.2017 um 06:08 in
Nachricht <b73e61f9-e689-72bc-ddc0-b74031ce8183 at jmvalin.ca>:
> On 10/31/2017 07:08 PM, Ulrich Windl wrote:
>> as MP3 and Opus have very similar objectives, I think the original poster's
>> question was a valid one: Why does Opus have more artefacts in the lower
>> frequency ranges than MP3 has?
> I'm not sure, but my best guess would be "because MP3's window is very
> leaky and MP3 has to waste a lot of bits in the LF because of that". It
> could also be just the MP3 encoder being silly, or other things. Most
> logical explanations would be related to MP3 being bad than anything else.
>> The spontaneous suspect that lower frequency
>> artefacts may be more noticeably than higher frequency artefacts seems
>> plausible, also. Is it a matter of energy (which is higher for higher
> Most signals have more LF energy than HF, so it's normal for the noise
> to look like that as well. If the noise is flat, then you have too much
> HF noise and you're wasting bits in the LF. In fact, that's exactly what
> I'm noticing in the spectrograms that are posted.
>> When your own ears are no longer in their best possible condition, you may
>> a spectrogram, just to make sure you don't miss anything.
> Actually, that's the wrong way. Especially when the spectrogram is
> computed on a signal difference. For example, some codecs can alter the
> phase (or add a small delay) in a way that's imperceptible, and yet
> causes a large difference signal. At the same time, artefacts such as
> pre-echo will not be noticeable on the spectrogram of the difference
> signal -- even when it's audible and annoying.
> The least bad way of estimating how good a codec is at very high bitrate
> is to just measure the point where you can't ABX and assume that all
> codecs improve by about as much per kb/s once that point is reached. And
> that's mostly true.
Unfortunately (as I pointed out) young children (those with the good ears) are rare among the developers (and rare as a resource for developers, I'm afraid).
Is there any analytic tool that can substitute good ears? Or don't we know how audible perception works, still? ;-)
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