Re: A Session In The Abyss: xHE-AAC vs OPUS at 12, 24 and 32 kbps (voice & music)
Reply #41 – 2021-05-26 14:36:23
At 12 kbps Opus is totally lost on music; it performs significantly better on voice but quality is not truly convincing. The overall result is very poor: sound is muffled , mono-ish, and there is often a bad amount of noise/grain. That's why I tend to use a bare minimum of 13kbps for Opus (v1.3) when it comes to speech since, at least off the top of my head from my previous playing around with Opus on speech (on my Klipsch Pro-Media speakers, which are above average PC speakers), that any lower than 13kbps, the sound quality starts to decline much more rapidly (i.e. the minimal storage space gains are no longer worth any further decline in sound quality). it seems to clean up the muffled aspect a bit going from 12kbps to 13kbps as I think that's ultimately why I settled on 13kbps as a bare minimum on speech. NOTE: although if one wants to play it a bit safer they could try 16kbps or 24kbps or 32kbps as, off the top of my head, I can't see using any more than 32kbps with Opus for speech as I am of the mindset that I don't need near perfection on speech and would rather go for storage space efficiency. so, at least in my opinion, don't use Opus any lower than 13kbps for speech as a general rule as I would say it's a good starting point for someone trying to find a really low bit rate to use on their speech encoding. I realize that it's possible, depending on the type of voice, that 13kbps might vary a bit. but still, it's probably not going to be bad enough for me to avoid if I want to store plenty of speech (especially if one is not too fussy on speech quality) and keep the file size minimal. one last thing... at least based on 13kbps, I can't see Opus for speech only having a slightly higher score than music (i.e. call it roughly 1.4 vs 1.8 which is in the 'annoying' and 'very annoying' section of the 1-5 rating system used around here (although I get the OP used 12kbps and not 13kbps like I am generally referring to)) because of this obvious thing for me... speech is usable, unlike music @ 13kbps (NOTE: although considering the VERY low bit rate, the music could be worse ) ; NOTE: I am not dissing the OP (as I thank the OP for the effort), just making a point is all. and.... ...I would say Opus @ 13kbps is no worse than the 'slightly annoying' range on the 1-5 scale (i.e. (5)"Imperceptible", "Perceptible, but not annoying", "Slightly annoying", "Annoying", (1)"Very annoying"). because while you can notice the quality decline vs a higher quality source file, it's not a significant enough of a decline for me to flat out not use it and it's great for keeping passable sound quality speech at a very low file size, especially if you got a lot of speech (say many hours) to store as this greatly increases storage space efficiency. or another way to put it... I would consider 13kbps to be more Thumbs Up than Thumbs Down for whatever that's worth, although 12kbps and lower I start to shift more to Thumbs Down than Thumbs Up for speech as a general guideline for those seeking to use the lowest possible speech bitrate. p.s. so I think music, unlike speech, most people would tend to be more picky on obtaining a higher quality for that where as speech as long as it's clear enough and easy enough to understand what's being said, then it's 'good enough'. like I can easily tolerate speech quality that's noticeably lower than 'transparent' than I could with music where a little decline here and there can be okay but if it becomes more obvious I just tend to play it safer with a higher bitrate. for the record... I can easily use Opus @ 64kbps for music as while I can go lower to say 48kbps etc, it's no longer worth the minimal storage space savings for the sound quality hit (I think 64kbps Opus is a safe minimum for music for the common person in my estimations). so I am more of the mindset to use Opus @ 13kbps for speech (minimum) and 64kbps for music (minimum). like I have mentioned before with Opus on music, I think if someone is happy with MP3 @ V5 (130kbps), it's plausible Opus @ 64kbps will be good enough to (even though I was told a while ago that Opus @ 80kbps is more of a equivalent to MP3 @ V5, but I think the average person probably won't notice it even though those around here might etc).