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Topic: forced stereo (-m s) with -aps/V 2 (Read 33956 times) previous topic - next topic
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forced stereo (-m s) with -aps/V 2

is it a larger bitrate, same quality? or is it both "lower quality" (as the joint stereo advocates like to point out) AND larger birate?

(yes, i still like to "fake" surround sound with the KB 5.1 audio out plugin -- after a couple years of a break from it :)

forced stereo (-m s) with -aps/V 2

Reply #1 –
It's a good question I've wondered about.

Clearly if joint stereo uses 320kbps for a frame and encodes it as M/S, then forcing discrete stereo can/will result in lower quality, possibly audibly so, since a higher bitrate is required to maintain the same quality, but the higher bitrate is not available.

As for the rest of the time, who knows? I was looking at the issue of mono encoding, and found that lame's psy model didn't behave as expected, so it's always possible that you might unearth hidden "features" by forcing discrete stereo, since all testing and tuning for this mode/preset has been carried out using joint stereo.

Cheers,
David.

forced stereo (-m s) with -aps/V 2

Reply #2 –
I just tried this with two test files using LAME 3.97.


File 1 (this has quite average channel separation, the stereo effect is clearly audible):

-V 2 --vbr-new resulted a 209 kbps mp3 file with 63.9% ss and 36.1 % ms frames (according to EncSpot Pro).
-V 2 --vbr-new -m s resulted a 212 kbps mp3 file.

File 2 (this is near mono):

-V 2 --vbr-new resulted a 179 kbps mp3 file with 8.3% ss and 91.7 % ms frames (according to EncSpot Pro).
-V 2 --vbr-new -m s resulted a 190 kbps mp3 file.


I may be wrong, but I would like think to that fully preserving the same quality would need a bigger bitrate increase. I didn't try to ABX the difference.

Edit: fixed a typo

forced stereo (-m s) with -aps/V 2

Reply #3 –
With a bit identical dual mono file, I get...

114.8kbps for joint stereo (100% M/S)
197.7kbps for discrete stereo (100% L/R)
100.4kbps for mono (100% mono!).

To get an idea of the coding noise (which I don't claim to hear, never mind ABX!) I inverse mix pasted the original over each version and get an average / maximum / total RMS error of...

joint stereo -40.91 dB -39.27 dB
discrete stereo -39.18 dB -27.58 dB -37.46 dB
mono -39.19 dB -27.58 dB -37.48 dB

So nearly 2dB lower coding noise for joint stereo than discrete stereo.

(And, interestingly, nearly the same noise for forced discrete stereo as for mono, implying that discrete stereo really does treat the audio as two independent mono signals. I inverse mix pasted the mono and discrete stereo version, and found them to be bit identical apart from maybe ~100 52ms frames out of 8340 frames. In the -m m version, 52 frames were over 160kbps, so that accounts for much of the difference, since this would imply more than 320kbps would be needed to maintain these frames in discrete stereo).


In short, for -V 2 --vbr-new in lame 3.97, discrete stereo encoding of a dual mono file is apparently bit-identical to mono encoding of the same file, except where the maximum bitrate limit is reached, and maybe in some other rare unknown circumstance (unless I miscounted - more likely!).

Joint stereo is objectively more accurate.

No ABX or listening test results supplied or offered, no relevance to audible problems claimed (though, to me, it suggests discrete stereo or mono is either more efficient (if you can't hear the difference), or audibly worse (if you can), than joint stereo).

Cheers,
David.

forced stereo (-m s) with -aps/V 2

Reply #4 –
Quote from: plonk420 on
is it a larger bitrate, same quality? or is it both "lower quality" (as the joint stereo advocates like to point out) AND larger birate?

(yes, i still like to "fake" surround sound with the KB 5.1 audio out plugin -- after a couple years of a break from it

I use KB5.1 myself  (matrix with L/R duplicated to the rears, vorbis q0  ).  If you are actually using the 'rear' channels in that plugins settings.. then I would avoid joint stereo if I were you.  Plain stereo will give you better seperation in the rear channels, and you can avoid the headache of ringing/flanging/distortion nastyness 

When I tested this (by the way 'centercut' can be used for the test as well) I only used low bitrate mp3 (~112kbps).  The only thing I was concerned about in my test was the channel separation, which was much better with plain stereo.

Considing how you will be using these files, I would go with plain stereo regardless of the 'potential quality loss if you "need" more than 320kbps for a frame'.
Vorbis-q0-lowpass99
lame3.93.1-q5-V9-k-nspsytune

forced stereo (-m s) with -aps/V 2

Reply #5 –
112kbps mp3 with forced discrete stereo. I think I'm going to be sick...!

(I assume it was just for testing).

Cheers,
David.

forced stereo (-m s) with -aps/V 2

Reply #6 –
Without M/S stereo, a track with vocal in the center can't be well encoded. Here (TomsDiner) is a example. I think you can abx these two of mp3.

I'm not sure V2 has same scenario. -m s can fix rare stereo issue but mostly decrease efficiency.

forced stereo (-m s) with -aps/V 2

Reply #7 –
Contrary to the current trends these days (which I've found is followed more religiously on popular audio forums such as this one, compared to the mp3s I actually find for download...maybe it's the type of music I'm interested in) at high bitrates I'm still a big supporter of forced plain stereo, or even dual-channel, as opposed to joint-stereo (forced or switching).

A lot of my encoding preferences have to do with encoding philosophy, rather than a direct demand for the highest quality possible. At 320 kbits/s, practically everything will be encoded transparently whether in Stereo or Joint Stereo, and the few samples that might have noticeable artifacts could still have artifacts even with Joint Stereo (in other words, a true 'problem sample' at 320 kbits/s is unlikely to be fixed by increasing bitrate further via Joint Stereo, it's more likely to be a 'problem sample' that exists regardless of bitrate). Furthermore, the most difficult-to-encode frames are highly likely to have a high stereo separation and LAME would encode those frames in L/R mode anyway, so Stereo vs Joint Stereo would be the exact same quality for that frame. Finally, from a philosophical standpoint, at high bitrate sometimes 'worse quality' is actually better. At 320 kbits/s one might aim for 'consistency' of audio quality rather than the 'best possible audio quality at all times.' For example, you might have a song where a complex sound is coming out of the center, then moves around to the left and/or right sides. If you encoded with Joint Stereo, it is possible that the complex sound would be encoded transparently when in the center, but sound slightly artifacted when it moves to the side(s). If you encoded with Stereo, that complex sound would always be slightly artifacted but at least it would always be artifacted the same...this could be preferrable and less bothersome, especially if you didn't have the source WAV and don't know that your sound is slightly artifacted to begin with.

Quote from: haregoo on
Without M/S stereo, a track with vocal in the center can't be well encoded.
I disagree, especially at higher bitrates. If you use LAME, many of your audio frames will be encoded in L/R mode anyway, so your 'vocals in the center' will be just as bad (during the most difficult-to-encode parts that have other instruments with stereo separation, in addition to your center vocals) during those times whether you encode in Stereo or Joint Stereo. In the best-case times though, the vocals in the center will be better encoded, but that would mostly only be a concern for low to medium-bitrate encodings (128 and 160 kbps, possibly 192 and 224 kbps as well).

forced stereo (-m s) with -aps/V 2

Reply #8 –
Quote from: 2Bdecided on
Clearly if joint stereo uses 320kbps for a frame and encodes it as M/S, then forcing discrete stereo can/will result in lower quality, possibly audibly so, since a higher bitrate is required to maintain the same quality, but the higher bitrate is not available.
I've wondered about this also, but I have several ideas on this issue that make me think that Stereo VBRs should not be lower quality than Joint Stereo VBRs, just bigger.

1) On the LAME Joint-Stereo VBR histograms, I noticed that the 320 kbps frames are in general mostly L/R frames anyway, very few M/S frames...compared to the lower bitrate frames. And for songs with extreme stereo separation at all times, practically the whole song, or exactly the whole song, can be L/R frames for the 320 kbps frames.

2) For the rare 320 kbps M/S frames we see, we don't know that LAME really thinks it needed the full 320 kbps. Maybe it thinks it only needed 270 kbps, but since there is no such thing as a 270 kbps frame it chose 320 kbps in M/S mode. And that same '270 kbps frame' in M/S mode might be encoded just as good in 320 kbps in L/R mode.

3) There are also potential bit reservoir issues, as LAME's VBR modes supposedly don't make very intelligent use of the bit reservoir. But supposedly it is still in use. The big reservoir could easily 'rescue' the very very rare potential 320 kbps M/S frame that you forced into L/R by encoding in Stereo.

To add to this, there are the 'philosophical' issues I discussed in my previous post, although admittedly that 'philosophy' is less consistent with the philosophy of VBR encodings (though it is still reasonably compatible IMO) and is more consistent with the philosophy of CBR encodings. But anyways, bottom line is that in my opinion Stereo VBRs are just bigger than Joint-Stereo VBRs, but not of any worse quality. That being said, when I personally encode VBRs (even high quality -V 0 ones) I generally use Joint-Stereo since I think the point of VBR is to save space and Joint-Stereo does save space. When I encode 320 kbps CBRs I generally use Stereo, due to my philosophical reasons I mentioned before. Also, in general I encode almost everything in CBR, not VBR, because I think VBRs aren't really worth it most of the time. But I encode certain things in VBR such as quasi-mono signals, or tracks (especially non-music ones) with large periods of silence inside, etc.

Anyway those are just my personal thoughts and reasonings, I don't have strong feelings on this matter (both Joint-Stereo and Stereo, VBR or CBR, can be great as long as the bitrate is high enough and a good encoder without broken switches is used -- although what I think is broken is not always in agreement with the general audio community) and don't mind if people disagree with me.

forced stereo (-m s) with -aps/V 2

Reply #9 –
Quote from: Porcupine on
Quote from: 2Bdecided on
Clearly if joint stereo uses 320kbps for a frame and encodes it as M/S, then forcing discrete stereo can/will result in lower quality, possibly audibly so, since a higher bitrate is required to maintain the same quality, but the higher bitrate is not available.
I've wondered about this also, but I have several ideas on this issue that make me think that Stereo VBRs should not be lower quality than Joint Stereo VBRs, just bigger.

1) On the LAME Joint-Stereo VBR histograms, I noticed that the 320 kbps frames are in general mostly L/R frames anyway, very few M/S frames...compared to the lower bitrate frames. And for songs with extreme stereo separation at all times, practically the whole song, or exactly the whole song, can be L/R frames for the 320 kbps frames.

2) For the rare 320 kbps M/S frames we see, we don't know that LAME really thinks it needed the full 320 kbps. Maybe it thinks it only needed 270 kbps, but since there is no such thing as a 270 kbps frame it chose 320 kbps in M/S mode. And that same '270 kbps frame' in M/S mode might be encoded just as good in 320 kbps in L/R mode.

3) There are also potential bit reservoir issues, as LAME's VBR modes supposedly don't make very intelligent use of the bit reservoir. But supposedly it is still in use. The big reservoir could easily 'rescue' the very very rare potential 320 kbps M/S frame that you forced into L/R by encoding in Stereo.


None of those explain why quality should be the same.  Only why it might not be substantially worse.

Quote from: Porcupine on
To add to this, there are the 'philosophical' issues I discussed in my previous post, although admittedly that 'philosophy' is less consistent with the philosophy of VBR encodings (though it is still reasonably compatible IMO) and is more consistent with the philosophy of CBR encodings. But anyways, bottom line is that in my opinion Stereo VBRs are just bigger than Joint-Stereo VBRs, but not of any worse quality. That being said, when I personally encode VBRs (even high quality -V 0 ones) I generally use Joint-Stereo since I think the point of VBR is to save space and Joint-Stereo does save space. When I encode 320 kbps CBRs I generally use Stereo, due to my philosophical reasons I mentioned before. Also, in general I encode almost everything in CBR, not VBR, because I think VBRs aren't really worth it most of the time. But I encode certain things in VBR such as quasi-mono signals, or tracks (especially non-music ones) with large periods of silence inside, etc.


Theres no delicate way to put this, so I'll be blunt:

Your philosophical approach to audio compression is stupid, and no one cares about it.  Maybe you could stop posting about it.  It makes wading through your posts annoying.

forced stereo (-m s) with -aps/V 2

Reply #10 –
My philosophy is to reject all philosophical musings on a subject backed up with objective scientific and mathematical theories.

Why don't you just, you know, move on to a forum better suited to your philosophy since you apparently regard Hydrogenaudio as 'religious', when I have seen this forum take flak for being too scientific.

As an aside, I am disappointed whenever I see a non-joint-stereo mp3 file encoded with Fraunhofer.

forced stereo (-m s) with -aps/V 2

Reply #11 –
My dear Porcupine,
448 words, 2063 characters in one post, but where is the sense?

forced stereo (-m s) with -aps/V 2

Reply #12 –
You thought that was bad...
http://www.hydrogenaudio.org/forums/index....=54109&st=0

Honestly though, he does like to pontificate verbosely with little (if any) supporting evidence.

forced stereo (-m s) with -aps/V 2

Reply #13 –
I was under the impression that statements made here at HA were to backed by objective evidence, not unsupported philosophical musings with no basis in empirical reality. As people in this thread have already pointed out, that reality suggests that forcing stereo frames usually leads to lower quality because:

a) Problem samples exist at 320kbps even when using M/S coding (i.e., fatboy, trumpets, etc). Forcing stereo frames starves the already insufficient bitstream of bandwidth, which can only harm quality.

b) Especially when using --nssafejoint (which is enabled by default on the higher presets), joint stereo is lossless.

c) As demonstrated earlier in the thread, forcing stereo frames also leads to higher quantization/coding noise (though it's arguable as to whether anybody could hear it).

Unless you have data to support the contrary assertion that forced stereo is better than joint stereo, please stop  pontificating about it. Hypothesizing is one thing, but making statements that are directly contradicted by established fact is quite another.

forced stereo (-m s) with -aps/V 2

Reply #14 –
damnit guys... can't you see that plonk420 is just trolling?  Mods, this issue has been discussed to DEATH... let's just end it now...

forced stereo (-m s) with -aps/V 2

Reply #15 –
Seemed like an honest enough question to me.

I think haregoo addressed it rather nicely giving us an example of where a forced stereo track was both larger and had more artifacts.

forced stereo (-m s) with -aps/V 2

Reply #16 –
It seems to me that with most of you guys here, any opinions/thoughts/arguments that do not agree with the popular principle on this board (which is not necessarily agreed upon in other venues, as I noted before) get attacked by many (not all) hydrogenaudio members in a completely unreasonable and illogical manner. Oh well.

> As people in this thread have already pointed out, that reality suggests that forcing stereo frames usually leads to lower quality

I may not have provided any ABX logs or samples for download, but I made no claims that what I said I have tested empirically. What I said were merely philosophical arguments, that are extremely difficult or impossible to test empirically. Even though I have provided no "empirical evidence", no acceptable empirical counter-evidence has been given either. What I am discussing is not really something that lends itself to empirical testing, for some reason this board seems totally against such ideas.

I should also remark that this thread was started by someone who does not necessarily conform to this board's views either, so he should be the one to say whether or not my thoughts are welcome, not the 'hecklers' on this forum.

> Problem samples exist at 320kbps even when using M/S coding (i.e., fatboy, trumpets, etc). Forcing stereo frames starves the already insufficient bitstream of bandwidth

Many (not all) problem samples at 320 kbps are the result not of insufficient bitrate, but of more fundamental flaws in the mp3 codec and or encoder itself. Do these problem samples (fatboy, etc) play flawlessly at a higher bitrate than 320 kbps? If they do, then your argument has merit. If they have never been demonstrated to play flawlessly as a mp3 before, then you can't assume the problem is due to a lack of bits.

> Especially when using --nssafejoint (which is enabled by default on the higher presets), joint stereo is lossless.

I never said there were problems with using joint stereo in LAME. I only said that stereo mode can be just as good as joint stereo mode in certain ways, especially when you consider that LAME performs joint stereo switching between L/R and M/S mode. The majority of frames in high bitrate mp3s are encoded in L/R mode anyway, and for those frames Joint Stereo and Stereo should have the same output.

> Unless you have data to support the contrary assertion that forced stereo is better than joint stereo, please stop  pontificating about it.

I never said that 'forced stereo is better than joint stereo'. And in regards to me speaking only on subjects that meet your approval, I refuse to obey you. However, if a mod asserts that your desire is also the desire of this forum, I'll probably be banned from this forum (and IMO this forum will not look very scientific to an outsider, if people are banned for arguing mathematical/philosophical points). An emphasis on empirical data is good, but this forum goes far overboard in my opinion. Empirical data with no mathematical analysis is arguably just as unscientific as mathematical analysis without empirical data.

> Hypothesizing is one thing, but making statements that are directly contradicted by established fact is quite another.

Well, you haven't provided the counter-evidence, at least not here.

forced stereo (-m s) with -aps/V 2

Reply #17 –
> None of those explain why quality should be the same.  Only why it might not be substantially worse.

Yes, that is a very good point. And I knew that from before, and I agree with you here. What I said proves nothing, it only argues that Stereo VBRs *might* not have substantially worse sound quality than Joint Stereo VBRs.

To actually choose to encode Stereo VBRs, one would really have to dislike Joint Stereo for other reasons. One such reason could be the 'philosophical' reason I mentioned earlier, but for me that's not a good enough reason so I encode my own VBRs in Joint Stereo. But to me, my 'philosophical' reason is a good enough reason to encode *320 kbits CBRs* in Stereo. That's just my own opinion.

> Your philosophical approach to audio compression is stupid, and no one cares about it.  Maybe you could stop posting about it.  It makes wading through your posts annoying.

I do not mind if you think my philosophical argument was stupid. I am not trying to convince everyone. I am merely trying to point out a different point of view, and everyone can decide for himself or herself whether or not my arguments have merit. To say that 'no one cares about it' is obviously wrong. A lot of people (not on this board) still prefer Stereo over Joint-Stereo for high-bitrate encodings. Most of these people probably care about my arguments.

If you find my posts annoying, you don't always have to respond to them. I appreciate the fact that you are a much more serious poster than some of the others here, but I can tell that even you don't have 100% good intentions when speaking to me. You are probably 90% genuine, 10% heckler (in my opinion). But I do greatly appreciate that your posts do add to the discussion, in general.
 

forced stereo (-m s) with -aps/V 2

Reply #18 –
Quote from: greynol on
I think haregoo addressed it rather nicely giving us an example of where a forced stereo track was both larger and had more artifacts.
He gave us ONE example of a V 5 sample. For one thing, he himself said that he wasn't sure if the same thing applied to V 2, which is the topic of this thread. I am not saying his sample is completely invalid, but it doesn't prove anything definitively (just as my own philosophical arguments don't prove anything definitively, as well).

But I'm still curious, in haregoo's V 5 sample, are the distorted frames on the Forced Stereo version all 320 kbps frames? Because if they were, then that would mean that the 320 kbps L/R frames indeed introduced audible artifacts that were gone in the higher "effective" bitrate afforded by M/S mode, and Joint Stereo should be necessary to encode that sample well (at any V value). But if they weren't 320 kbps frames, then that would suggest that the the problem lies more with the way LAME behaves at V 5 (and with medium-to-high V values in general) rather than a true problem with Stereo mode. Because in theory, it could be argued that LAME should be trying to make a V 5 Joint Stereo file sound the same as a V 5 Stereo file, so the encoder could/should have simply shrunk the size of the Joint Stereo version more, until it sounded 'just as bad' as the Stereo version. I guess these would be interesting things to test if anyone cares.

forced stereo (-m s) with -aps/V 2

Reply #19 –
Quote from: Porcupine on
To say that 'no one cares about it' is obviously wrong. A lot of people (not on this board) still prefer Stereo over Joint-Stereo for high-bitrate encodings. Most of these people probably care about my arguments.


I doubt it.

forced stereo (-m s) with -aps/V 2

Reply #20 –
Quote
As an aside, I am disappointed whenever I see a non-joint-stereo mp3 file encoded with Fraunhofer.


I can argue that joint-stereo implementation in most (if not all) Fraunhofer encoders is not good enough to replace plain stereo at relatively high bitrates (>128 kbps). Lame is the only MP3 encoder having good non-agressive M/S implementation suitable for high bitrates.

forced stereo (-m s) with -aps/V 2

Reply #21 –
It has been pointed out in other threads that while sound sources that are mostly in the left or mostly in the right channel are best encoded with L/R frames, the same is not true for sound sources that are near the center.

This is quite logical since the separate processing of left and right channels can result in slightly different rendition of the center, differences that taken by themselves are insignificant perhaps, but since our ears process them together to create a sound image of the center, the two sources are now slightly inconsistent, making for a distortion.

If instead the frame is encoded as M/S then the center can be accurately encoded, since the center is processed by itself and is not affected by what is going on to either side. Also, I think that sound imaging of sounds near the center is more importand than sounds to the far left and right.

The advantage of M/S over L/R in this situation becomes smaller as you increase the bit rate, but I guess philosophically I just don't want to take the chance that the difference might be audible, even at 320 kbps.

forced stereo (-m s) with -aps/V 2

Reply #22 –
At higher bitrates you can think offensive instead of defensive. Go for joint stereo and psychacoustic enhancements rather than the typical brute force approach [CBR/ABR/ LR Stereo]. That way you are maximizing quality in most cases rather minimizing it in most cases because of the rare problem sample.

At 320k if you can't hear the difference - leave it on !

forced stereo (-m s) with -aps/V 2

Reply #23 –
Though theoretically I am also a tiny bit concerned about joint-stereo (theoretical possibility of switching problems L/R <-> M/S representation, adequate psy model for the side signal which is a difference signal) I don't care a bit about it as I don't know a single sample where this bothers me, and I am well aware of joint-stereo's part in efficient and/or increased quality encodings.

That's why I use joint-stereo with my Fraunhofer encodings though it seems that the Fraunhofer people don't have very much cnofidence in their joint-stereo implementation as they use plain stereo above CBR 192 kbps. (The alternative would have been to use 256 kbps or 320 kbps plain stereo to make up for a compensation of the inferior data representation of plain stereo, but I'm very happy with my 192 kbps joint-stereo encodings).
lame3995o -Q1.7 --lowpass 17

forced stereo (-m s) with -aps/V 2

Reply #24 –
Pocurpine,

As a daily member of this forum for so many years, I would like you to *not* assume what this forum is and/or accepts as valid talking.

In this forum you will not find comments like "windows is shit, use linux", "macs foreva" and so on.

Those are oppinions (in this case clearly "fanboy") which might be valid, but only to a very limited situation.

Neither in this forum you'll find talks about "god exists", or any other religius content.

Those are believings, things that might, or might not exist, which empirically can't be demonstrated, and that objectivically, it has to be labeled as a believe, or has to be faced that evidence on the existance is not found, or is difficult to demonstrate.

The discussions in audio related threads many times suit those two groups:
oppinions about this codec/setting to be the best thing ever, and believings in expensive hardware that supposedly does this and that, when there's no evidence about it.


Hydrogenaudio refuses, energically, to accept anything that is both, non demonstrable, and that contradicts the knowledge that this forum has been  accumulating over tests and tests, done in a controlled and repetitive environment.

So if you don't agree with the "modus operandi" of this forum, you are the one to change, not the forum.



Back on topic:

The encodes with -m s in VBR show an increased bitrate. The encoder supposedly is doing so in order to maintain the expected quality (it is, otherwise logical that a L/R representation uses more bits than a M/S one in the general case).

So the discussion obviously needs to go between what happens to L/R stereo if it has not enough bits, versus what artifacts can appear in a M/S representation which wouldn't exist in a L/R representation, *specifically* talking in the context of a (well tuned) MP3 encoder.

[Edit -> corrected some M/S L/R typos]