They say anything less than 192kb/s kills surround in 2 channels, but my question is what is lowest possible bitrate one can use in a 5.1 track and get away with?
I have done some avi's with 5.1 tracks at 224kb/s and they are perfectly acceptable, all channels playing correctly, and " any absence of punch in sound" is not that noticeable in speakers. Tried 192kb/s and it was okay too, but maybe 160kb/s is the absolute working limit without damaging surround effects!
Is 128kb/s theoretically possible or just a waste of time?
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Stereo = 2
5.1 = 6
128k = minimum for 2
128kx3 = 384k for 6
Anything less sounds like ass. Easy to hear loss. Closer to telephone or FM/AM radio quality.Want my help? Ask here! (not via PM!)
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So it is probably better to have a 2 channel mix as prologically/stereo if bitrate if lower with speaker set up. I agree with what you are basically saying if the environment is "perfectly set up" for surround replication eg Home cinema, but any ac-3 source(especially a mix 5.1)always sounds much subjectively better on 2 channel/speaker set up via HD TV despite the bitrate in my "amateur" tone deaf hearing tests.
Off topically, I'm no expert but FM sound is okay qualitywise. SoopaFresh's AVI gain using soopaloud option produces similar to FM stereo and it sounds great! I suppose it is all to do with how purist you are or how trained your ears are to dynamic ranges! By the 224kbs ac-3 sounded okay through a correct 5.1 set up to me. Isn't all this a bit subjective really regarding ac-3 bitrate? -
How much joint stereo-ing does 5.1 surround make use of? Or are all the channels separate?
I'll say this much, either you've got very unchallenging material, an incredible encoder, or cloth ears. Some of the rates you're posting are my lower limit for stereo, much of the time. I'd happily shave a little off the video rate to up it to 384 or higher with full surround. Say, going from 4100 to 3900kbit average won't make a hell of a lot of difference to the image quality vs the 3x improvement in audio bitrate.
Using MP2 with a good encoder: can tolerate 128k or even 112k for some stuff, when doing e.g. an exceptionally long play single-disc VCD, if it's prefiltered. Most of the time 160k is on the borderline for it starting to suck, and 192k is preferred (224-256 if there's space going begging).
MP3s in AVIs... you can do 64-96k joint stereo if getting hi-fi quality isn't too critical (like, recording a debate or something), but really you want at LEAST 128k, preferably 160-192 CBR. Best of all is VBR (set such as to give you 120-200k, average) if the player can support it, as just like VBR video it makes the best use of very variable material.
AC3 is presumably a smidgen more advanced than MP3, but maybe not as much as AAC. So if you pushed it, you may get away with 96-112k per pair of channels, IF there's sufficient interchannel masking going on (so, ~256-320kbit for 5.1). You may still have moments of iffiness even so, and if they're actually all separate, it'll exacerbate the problem. 48k per mono stream is NOT much, particularly with the breadth of material typically present in a DVD soundtrack. Now, for your idea of 128... /6 = 21k/speaker. We're talking internet radio kinds of bitrates, here.
There's a reason it allows you to crank it up to something crazy like 640kbit, after all...
(Too bad they didn't allow for VBR coding though.... it'd take a huge chunk out of the required bandwidth in scenes where everything's happening "up front")
EDIT:
Prologic could be a good alternative, if you have some way of producing it (I think BeSweet does?). Note however that you don't get full 6-way output - there's no separate bass track, the rear speakers are mono, "surround" and "centre" are subject to a 7khz lowpass filter (might not notice this?) - and if it's the older standard (or a poor decoder) you don't even get "centre" anyway. Plus you'll STILL need a higher bitrate in order to preserve the differential information required, as it was originally defined as a standard for analogue broadcast. Be nice if there was a purely digital version
I did some testing with it with MP2 on a VCD, after finding a source AVI with 5.1 AC3 audio (by accident - pain in the ass getting it to work!) and it seemed to come across well, when the bitrate was high enough (224k I think preserved most of it, though if I was to only listen to the surround speakers it would probably have sounded like crap given that the MP3 was HIGHER rate; you might be able to use, say, 160-192k for AC3 before the illusion breaks down). Luckily I had a DVD player with a built in prologic decoder that generated its own subwoofer track and a recently bought set of cheap surround speakers to test withLast edited by EddyH; 27th Apr 2010 at 13:46.
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Back after a long time away, mainly because I now need to start making up vidcapped DVDRs for work and I haven't a clue where to start any more! -
Eddyh charmingly writes: I'll say this much, either you've got very unchallenging material, an incredible encoder, or cloth ears.
Your reply is very informative to my "cloth ears" in what I thought was a straightforward interesting basic query. Don't forget to remind me to use the same sort of polite aproach in my replying to others here? I have mixed loads of "challenging action avi's"to 224kb/s("tested" at 192/bs a few times but did not like result) and the effects are excellent using Soopafresh 2.0 to 5.1 tool.
Sometime in the future there will be 5.1 channels compressed to 128kb/s as the norm and still quality based. Matter of time!
640k is good in blu-ray but you could argue 448 is lossy again as is 384. 256/224 and so on, point here what is acceptable to you? Still compressed/lossy whichever way you look at it. Others prefer merit of DTS Yes it is an incredible tool by Soopafresh. You got that right. Thanks again.
Last edited by azmoth; 27th Apr 2010 at 14:24.
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I guess the "quality" of my English makes me tired, often.
@azmoth:
the "quality" of your ears is what it counts after all...
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