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Topic: Opus 96kbit vs 102kbit (Read 1071 times) previous topic - next topic
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Opus 96kbit vs 102kbit

Hi everyone,

i plan to convert tons of audio stuff with the opus codec. I browse on the office dokumentation and stopped
on the "intensity stereo threshold" part. ( https://datatracker.ietf.org/doc/html/rfc6716 / page 152 / table 66 )

So at 96kbit/s, Opus uses fullband (20khz) stereo, and the "intensity stereo threshold" starts around 19khz.
When you look at the table 66, the maximum bitrate in this range is 102kbit/s, higher bitrate ends into the
next threshold for 20khz IS. So 102kbit/s "maxed out" this range.

Opus supports bitrate settings that is not a multiple of 8 or 16, so why is the 96kbit/s so popular while 102kbit/s
would add a little extra safty margin without bloating filesize so much?

Re: Opus 96kbit vs 102kbit

Reply #1
As far as im aware, there is no real advantage of keeping the bitrate a multiple of something.
According to this listening test, i would go even higher to 128 kbit/s:
https://hydrogenaud.io/index.php?topic=120166.0
This bitrate is also mentioned in your source for music.
Your thouroughness makes me worried that you are going to delete your lossless collection?!

Re: Opus 96kbit vs 102kbit

Reply #2
i plan to convert tons of audio stuff with the opus codec.

In short... Opus @ about 64kbps and lower tends to play to Opus strengths because at about 96kbps, while Opus is a strong performer, you are better off sticking with AAC(AAC-LC) for near universal compatibility and once you hit about 128kbps+, MP3 (i.e. V5 (130kbps average) or better) tends to be the safest all-around choice given it's universal compatibility with lossy audio playback devices.

but if your pretty hardline on using Opus over AAC(AAC-LC)/MP3 then I would either choose 64kbps or 96kbps and forget about it. 64kbps if your more concerned with storage space savings, or 96kbps if your a bit more concerned with sound quality. I would not really consider any other bit rates with Opus for music personally because say 128kbps, while Opus is good, it's not a large enough difference over MP3 @ V5 (130kbps) to where it's worth losing wide hardware support over it.

because I tend to see minimums (which is typically what I suggest using for each format) for each encoder for music like this...

-Opus @ 64kbps (while you can go lower to say 48kbps or 32kbps etc, it's not really worth the limited storage space savings for any further risk to overall sound quality in my opinion)
-AAC(AAC-LC) @ 96kbps (Apple AAC... CVBR might be a little safer, but even with TVBR you can't really go wrong)
-MP3(LAME) @ V5 (130kbps)

so with that in mind and given wide hardware support you can see my general reasoning that it's not really worth using Opus unless you reach that range it's advantages start to become a bit more obvious to where it's worth considering sacrificing the universal compatibility of AAC/MP3, which is the 64kbps range and lower where Opus starts to legitimately shine over AAC/MP3.

hell, I suspect many people won't notice any obvious differences with Opus @ 64kbps because the core overall sound is intact vs original lossless source when they just sit back and enjoy their music. but even for those who like to play it on a side of caution with sound quality on Opus, use 96kbps and forget about it since it's pretty safe to say that will please nearly everyone given the listening tests around here.

but speaking of MP3... lately I just been sticking with MP3 @ V5 (130kbps average) since it's pretty much guaranteed to play on any device that supports lossy audio and sound quality is 'good enough' (especially given the public listening test around here) and is efficient. so it's one of those 'use it and forget about it' sort of things. because if someone needs higher sound quality they are probably best off just switching to FLAC if possible since the whole point in using lossy audio is lowest possible file size while still retaining overall sound quality that's close enough to transparency.

if it were speech, in regards to Opus, I think 'as low as' 13kbps is usable and is very efficient on storage space. but if one wants to keep speech quality transparent or thereabouts you will have to raise bit rate some. but in my opinion, at least for the most part, 13kbps offers a large portion of the sound quality at a VERY efficient amount of storage space. because speech, unlike music, does not need to be pretty much transparent. because I think with speech, as long as overall speech audio quality is clear enough, I would tend to opt for the storage space savings, especially if you have a lot of it and want to keep file size really compact.
For music I suggest (using Foobar2000)... MP3 (LAME) @ V5 (130kbps). NOTE: using on AGPTEK-U3 as of Mar 18th 2021. I use 'fatsort' (on Linux) so MP3's are listed in proper order on AGPTEK-U3.

Re: Opus 96kbit vs 102kbit

Reply #3
Thanks for the replay.

As far as im aware, there is no real advantage of keeping the bitrate a multiple of something.
This is the big question because 96kbit was a multiple of 8/16 and maybe the reason why 96kbit is more popular than 102kbit.

Your thouroughness makes me worried that you are going to delete your lossless collection?!
The audio content that i plan to convert around 96/102kbit/s, is indeed stuff that i would delete after conversion.
Mostly audiodrama, audiobooks with and without background music, interviews, short samples etc.
Music on the other hand, I allways keep a lossless copy and using opus@192kbit/s that perfectly fits my needs including most killersamples.
To keep things simple, i would using only two encoding profiles, 192kbit for music, 96/102kbit for all other content,
(the real bitrate is often lower on that content)

you are better off sticking with AAC(AAC-LC) for near universal compatibility and once you hit about 128kbps+
I was using apple aac many years now, and was transparent to me at Q91 (besides typical killer samples),
but there are exaclty 3 things that drives me crazy and pushing me to switch to opus.
1. "applaus / clapping hands" on around 96kbit
2. "breaking class noise" around 96-144kbit, because it's lowpass filtered ~17khz (i can hear upto 19,4khz)
3. "cymbal noise" from my old metal albums that is often easy abx-able upto 225kbit
So i must using a way higher bitrate as i usually would to bypass these problems.


Re: Opus 96kbit vs 102kbit

Reply #4
So at 96kbit/s, Opus uses fullband (20khz) stereo, and the "intensity stereo threshold" starts around 19khz.
When you look at the table 66, the maximum bitrate in this range is 102kbit/s, higher bitrate ends into the
next threshold for 20khz IS. So 102kbit/s "maxed out" this range.

You are misreading the table. The values on the right are "band numbers", not "kHz". See Table 55 on page 104 for the definition of the bands. Also, note that these thresholds are (kinda) optimized for overall quality, which means that 102 kb/s is just as likely to sound better or worse than 101.9 kb/s, since when you disable intensity stereo for a band, you also increase the amount of noise in that band. You could easily make an encoder that never uses intensity stereo -- it would just sound worse.