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View Full Version : Stereo vs. Joint Stereo **again**


MaTTeR
10th December 2001, 21:44
I'm sure this has been raised before on this board or other audio boards but I was wanting to hear what you movie/audio phreaks thought.

So is there ever a wrong time to use Joint Stereo? Maybe it's my ears but to me, when I encode with Joint stereo the voices seem more dominant out of my left speaker. I've noticed if I use --r3mix in LAME that it almost always encodes with J-Stereo. Then again on some other boards, I've seen people say they always use stereo. Any thoughts?

b0b0b0b
10th December 2001, 23:13
Was there ever a consensus on whether joint-stereo preserved the dolby pro logic info? Maybe it munges it enough that some receivers get confused.

MaTTeR
10th December 2001, 23:23
Originally posted by b0b0b0b
Was there ever a consensus on whether joint-stereo preserved the dolby pro logic info? Maybe it munges it enough that some receivers get confused.

I hadn't heard about this but that could certainly be why I hear the dialog mostly coming out of my left speaker. I'm in fact using the Sony DD/DTS receiver with an optical cable coming out of my Nightingale 6 channel sound card. Maybe the joint stereo screws with it. Not sure.

b0b0b0b
10th December 2001, 23:27
Can you can disable "processing" on your receiver? I can tell mine to play it as plain stereo, as opposed to trying process it as dolby pro logic/dd/dts.

If the balance changes then that might be a sign that the pro logic info is wrong.

Do you use --r3mix all by itself? I have actually gotten good results with it.

MaTTeR
10th December 2001, 23:45
Originally posted by b0b0b0b
Can you can disable "processing" on your receiver? I can tell mine to play it as plain stereo, as opposed to trying process it as dolby pro logic/dd/dts.

If the balance changes then that might be a sign that the pro logic info is wrong.

Do you use --r3mix all by itself? I have actually gotten good results with it.

Yeh, I can disable the processing feature and just send the reciever a multi-channel signal which is what I have been doing. This reciever detects if the audio is DD/DTS or Pro Logic, if it isn't it will default to normal stereo mode or 1 of the many simulated surround fields. If I play a true AC3 stream which is DD, then the processing will kick in and provide proper 5.1 balancing. It's only recently I noticed the sound balance issue after playing MP3 files which I encoded using --r3mix. It's the only option I use for all my movie sndtrx and I really like the quality except for the balance issue.

pacohaas
11th December 2001, 00:13
LAME does Joint stereo perfectly (unlike some encoders, audiocatalyst to name one) and if you want to make absolutely sure use the ns safejoint flag when you encode. JS will save bits and in CBR files it will actually have better quality than a stereo encoded file because of the wasted bits in stereo files.

Nic
11th December 2001, 11:16
Joint Stereo can sometimes cause a very slight "slurring" (not the right word - but you can probably guess what I mean) - But this is only everso slight, so Stereo should only be used when the bitrate is very high...else Stereo will lower the quality significantly.

-Nic

MaTTeR
11th December 2001, 22:41
Originally posted by Nic
Joint Stereo can sometimes cause a very slight "slurring" (not the right word - but you can probably guess what I mean) - But this is only everso slight, so Stereo should only be used when the bitrate is very high...else Stereo will lower the quality significantly.

-Nic

Ok. I'll keep all this in mind. I consider ABR 160-192 very high but I'm curious what you think when you say very high.

kxy
12th December 2001, 08:30
Check your bitrate, if you are using --r3mix default with joint, and the bitrate is dipping too low(my own meaning of low bitrate), around 130ish, it might cause the error you described. Most people can't hear that tho. Anyhow, basically, joint stereo is just a combination of stereo and mid/side stereo, chosen on a frame-by-frame basis by the encoder.

So enable r3mix with --nssafejoint, now the encoder should be MORE conservative in picking M/S vs Stereo.

I would suggest you do 3 test.
Encode
1) r3mix
2) r3mix --nssafejoint
3) do a stereo encoding
4) optional, pick your own switches to fit the sound material of the movie.

Then pick one from there.

MaTTeR
12th December 2001, 09:07
Great feedback guys. Many thx! I'm going to do some testing now and I'll report back.

Rhaegar Targaryen
12th December 2001, 16:14
Joint Stereo preserves Dolby Surround info for me... tested on Apoc Now Redux. ;)

MaTTeR
12th December 2001, 16:24
Originally posted by Rhaegar Targaryen
Joint Stereo preserves Dolby Surround info for me... tested on Apoc Now Redux. ;)

What do you mean it preserves the info? How are you converting the AC3 track? When you say Dolby Surround, are you saying that you can play the MP3 out of multichannels? Sorry for all the questions but I'm trying to nail down the whole audio encode process.

b0b0b0b
12th December 2001, 16:26
My understanding of dolby surround is it "works" with any audio signal. You will always get sound out of your center and surrounds, given any signal, even if no extra work went into encoding the signal.

Please correct me.

Rhaegar Targaryen
12th December 2001, 16:32
1. AC3 -> 16-bit WAV using Azid, no changes made to sampling rate (48KHz)
2. 16-bit WAV -> MP3 using Lame 3.89 --r3mix (which uses joint stereo)
3. Muxed with an .avi
4. Watched .avi in PowerDVD 4.0 XP, with it's Dolby Pro Logic II decoder enabled
5. The correct "rear channel" sound effects were being sent to the rear speakers of my 4.1 sound system (compared with DVD)

For reference, here is my system:

Windows XP
Turtle Beach Santa Cruz in 4-speaker mode
Using 4112 WDM drivers for Santa Cruz
PowerDVD XP 4.0
Altec Lansing ACS-56 4.1 speakers in analog multichannel mode
An AthlonXP CPU on a mobo using the KT266A chipset

tangent
12th December 2001, 16:33
LAME preserves dolby surround information in joint stereo. The reason some people prefer to use full stereo instead of JS is that JS occasionally causes JS artifacts.

Using -ms is not the best solution against the JS artifacts. Using -mj with --nssafejoint is better, because JS stereo frames are still used, but stricter so that they will not be used when using a JS frame will cause bad artifacts. --ns-msfix can be used to alter the JS threshold level.

It's really a trade off thing. If you use -ms, you won't get the JS artifacts but you lose quality overall because there are less bits overall to encode with.

For ABR encoding, I would just go with the lame --dm-presets which have the --nssafejoint and --ns-msfix value tuned to the particular bitrate.

Rhaegar Targaryen
12th December 2001, 16:36
Originally posted by b0b0b0b
My understanding of dolby surround is it "works" with any audio signal. You will always get sound out of your center and surrounds, given any signal, even if no extra work went into encoding the signal.

Please correct me.

not true... read the Dolby specs.

you need to perform a correct Dolby Surround downmix, so that Dolby Pro Logic decoders will correctly extract the channel information from the phase information that is matrixed into a 2-channel stream.

Azid and dvd2avi perform correct DS downmixes.

Maybe if you enable DPL or DPL 2 on a standard Stereo soundtrack you get "surroundish" effects, but those are not right or intended to be there... it just happens.

Those of you so concernced about maintaining Dolby Surround... WHY DONT YOU JUST TEST IT... if you can't test it, then it seems like you probably don't have any surround equipment. in that case, WHY DO YOU CARE? stuff like divx is time-limited, and within the span of 2 years you will (probably) find another codec which puts divx311a and divx4 to shame, so why are you even bothering trying to "futureproof" your rips by making sure the sound is surround even when you are just using a pair of $5 labtecs.

not to mention that "futureproofing" using an ancient technology such as dolby surround is downright ridiculous!

b0b0b0b
12th December 2001, 16:44
Maybe if you enable DPL or DPL 2 on a standard Stereo soundtrack you get "surroundish" effects, but those are not right or intended to be there... it just happens.


This is what I was getting at. I have a nice receiver, and it claims to implement dolby pro logic decoding. When I run a music CD through it that was clearly not dpl processed, I get vocals coming out of my center channel! All I'm saying is how do you even know it works. There's no DPL way of sending a particular signal exactly and only directly to a particular channel, is there?

All I know is I encode using --r3mix and it sounds fine to me (w/o dolby surround downmixing from ac3->wav).

MaTTeR
12th December 2001, 16:48
Originally posted by Rhaegar Targaryen

Those of you so concernced about maintaining Dolby Surround... WHY DONT YOU JUST TEST IT... if you can't test it, then it seems like you probably don't have any surround equipment. in that case, WHY DO YOU CARE? stuff like divx is time-limited, and within the span of 2 years you will (probably) find another codec which puts divx311a and divx4 to shame, so why are you even bothering trying to "futureproof" your rips by making sure the sound is surround even when you are just using a pair of $5 labtecs.

not to mention that "futureproofing" using an ancient technology such as dolby surround is downright ridiculous!

I'm not trying to future proof anything. I'm just looking for advice on to get the possible sound out of my entertainment system. All the advice and info above just saves me time in all my testing. My entertainment system is as follows-

Celeron 733
256MB RAM
80GB 7200RPM Drive
52x Creative CDROM
Nightingale 5.1 Pro6 with Optical
Sony 675 DD/DTS Reciever
Sony 140 Watt FL & FR Speakers
Klipsh 70 Watt Center
Kenwood 50 Watt RL & RR Surr Speakers

So...I'm definitely not working with $5 speakers here. Currently all my encodes sound great on the system but I've downmixed them to stereo. What I'm really looking to do is what you suggested with DPII using PowerDVD4. Thanks again for all the info guys!

Rhaegar Targaryen
12th December 2001, 16:49
how do you know what works?

err... try this. get a dvd that has a DS 2.0 192kbps AC3 audio stream *and* a DD 5.1 384-448kbps AC3 stream. Go to a scene with surroundish effects. compare how the 2.0 channel sounds, to how the 5.1 channel sounds. assuming your recieveer is only Pro Logic, and your dvd player "knows that" (i.e. since you only plugged in the rca left and right jacks) your dvd player should downmix the 5.1 stream to dolby surround. they should sound somewhat similar. and the DPL light on your reciever should be on (or maybe you'd have to turn it on manually...)

Rhaegar Targaryen
12th December 2001, 16:52
Originally posted by matter

So...I'm definitely not working with $5 speakers here. Currently all my encodes sound great on the system but I've downmixed them to stereo. What I'm really looking to do is what you suggested with DPII using PowerDVD4. Thanks again for all the info guys!

maybe you should try keeping the AC3 stream (are you working with Divx?) and outputting it via SPDIF to your fancy reciever there. that is definitely the best option for maximum audio quality.

i tend to only resort to MP3 tracks for 1cd rips and 2cd rips "taken to the limit" (i.e. 160minute fast action movie lots of daylight scenes 1.85:1 A.R. blahblahblah). obviously FP ratio is helpful in indicating whether to go for MP3 or keep AC3 in those situations. ;)

MaTTeR
12th December 2001, 17:14
Originally posted by Rhaegar Targaryen


maybe you should try keeping the AC3 stream (are you working with Divx?) and outputting it via SPDIF to your fancy reciever there. that is definitely the best option for maximum audio quality.


Depending on the movie I do keep the AC3 stream and of course it sounds great using the SPDIF. However, some movies I'd rather just have a really nice MP3 track when I'm shooting for 1 CD. So when you play your MP3 track on your reciever does your Doly light turn? Mine light only comes on if I'm playing the true AC3 track.

b0b0b0b
12th December 2001, 17:15
Rhaegar is right-- somebody should do a (blind?) A/B test to figure out exactly what effects are coming out of the rear and center channels when your receiver is doing dpl decoding. The cases are: (A) encode an mp3 from a DD 2/0 and (B) encode an mp3 from a DD 3/2 downmixed to dolby surround.

0. encode mp3's with -mj.
1. if A & B sound the same then use safejoint.
2. and if A & B still sound the same, try -ms.
3. and if they still sound the same, compare the original AC3 streams.
4. and if they still sound the same, start over with a different soundtrack.

Probably should start with step 3.

Or did somebody already do this? Rhaegar, were you saying you had done something like this with apoc now redux?

Do people really hear artifacts with -mj? Their ears are so much better than mine. I guess the key to good compression is to first ruin your ears.

b0b0b0b
12th December 2001, 17:16
Originally posted by matter


So when you play your MP3 track on your reciever does your Doly light turn? Mine light only comes on if I'm playing the true AC3 track.

I think he means dolby pro logic and not dolby digital.

Rhaegar Targaryen
12th December 2001, 19:12
Originally posted by b0b0b0b
Or did somebody already do this? Rhaegar, were you saying you had done something like this with apoc now redux?

yes

also, i have most of the dolby digital VOB trailers as well as AC3TEST.VOB which is perfect for testing these things. ;)

note that i did not need to use safejoint, just --r3mix made it work.

cheers...