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a response to a growing rumor...
Dibrom
post Feb 12 2002, 00:36
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Normally I wouldn't attempt to address an issue in this manner, but since it is getting a bit out of hand, and usually on boards I'm not participating in (or have little desire to participate in), I'll try and address it officially, once, in the place where it should be the most relevant.

The matter I'm discussing is related to the --alt-presets and their handling of the "stereo image".

There have been some completely unsubstantiated reports and rampant speculation going on in a few threads which I will list below:

1. http://66.96.216.160/cgi-bin/YaBB.pl?board...&num=1013124809
2. http://www.digital-inn.de/showthread.php?threadid=8212
3. http://www.hydrogenaudio.org/forums/showth...s=&threadid=759 (I simply hadn't gotten around to responding to this thread though its on this board).

At any rate, I'll try to make a few points as clearly as I can.

1. All of the --alt-preset VBR modes are tuned for "stereo image".

2. All of the vbr presets provide better sound quality via joint stereo than LAME on it's own with joint stereo, and in some cases should even sound better than with --nssafejoint, while at the same time providing a lower bitrate.

3. The --alt-presets do not, by design, make any sacrifice in regards to stereo image to keep bitrate down. Anyone who tells you this has no idea what they are talking about. I should know since I actually wrote the code and designed the presets.

4. An extremely high degree of stereo frames is not always needed to achieve good sound quality. I challenge anyone who believes that --alt-preset standard has poor stereo seperation, on a common basis (as a few unsubstantiated claims imply), to provide me with direct evidence of this.

5. Joint stereo is needed even at bitrates of 320kbps to achieve the best sound quality in some critical cases. Forcing stereo on everything up to 320kbps and then forcing joint stereo does not fix the problem (as user implies in one of those threads). I've tried this before.

6. There seems to be a misconception that all that the --alt-presets improve on are pre-echo. This is sorely mistaken. Indeed they do improve on pre-echo and impulse handling to a fairly large degree, but they also improve upon:

- joint stereo handling (serioustrouble is a prime example)
- dropout prevention (2nd_vent_clip is a prime example)
- fluttering (gekkou is a prime example)
- knocking (velvet is a prime example)
- ringing (bloodline is a prime example)
- noise pumping (piano, rach_original, etc, are examples)
- rasping (present with noise shaping 2 on some clips like fatboy, or on clean vocals sometimes. Mostly eliminated, even on the most critical samples, with --alt-presets)

And that's just the stuff I can think of off the top of my head.

Now, that's not to say the --alt-presets are perfect. I certainly know they aren't. But they also don't have some massive flaw in regards to stereo image which is present to the degree some people imply. In fact, the only case I've seen which I put any credence in is the few isolated cases which Wombat has found (and provided samples for I might add). I will eventually attempt to address these few samples, but note that these are exceptional cases, not common cases, and as far as I can tell, they are completely unrelated to the other complaints being made. This is especially so since Wombat doesn't describe the artifact as being a collapse of the stereo field (which isn't your typical joint stereo artifact in LAME anyway...).

At any rate, I'm always looking to improve things if I can, but claims must be substantiated which includes providing abx results (which are then verified by other parties) and providing test samples, preferrably multiple ones if you are implying a problem with general behavior.

Not to come across arrogant, but for the most part, I'm the only one who truly understands the workings behind the --alt-preset specific tunings. Not even the other developers have followed my work (though that's by their choice, not mine). The code is available for all to see, but so far I have not seen anyone attempt to reimplement my modifications or to discuss them with me on a technical level. So unless you see someone who is closely related to the work I've done (ie, they have participated in testing, JohnV for example) stating something, or you see me stating something directly about the presets, then chances are whoever is discussing the presets doesn't have the full picture. This is especially true when people begin discussing how the --alt-presets work internally or technically, and especially in relation to joint stereo.

If you see a discussion on another board about these issues, please point people to this thread. If you have a question, please ask me here, you'll likely get a much more correct answer in addition to helping to keep questions about this issue centralized and concise (which will help when the FAQs are created). Speculation is not only wasteful, but it also helps to propogate misinformation such as the old "joint stereo is bad" line of thinking.
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Dibrom
post Feb 14 2002, 00:03
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Pio2001,

It's a shame you didn't post your response to my graphs on this board here, but since I'm not registered at r3mix.net I'll just respond to it here.

Originally written by Pio2001
QUOTE
The pictures shown by Dibrom are interesting, but their interpretation is not easy.


Really? It seems as if they're not so easy to interpret in the context I discussed them in, only if you wish to interpret them that way (being difficult). The evidence is clear enough I think... how can you attempt to spin that?

QUOTE
[b]I'm not sure that APS shows more HF content than r3mix, because it rather shows a large band and large time of very low HF level, while r3mix shows short burst of high level HF (especially on the them sample).


Umm... so? Low level HF or not, it's irrelevant. The fact of the matter is that it is HF, and it is audible in some of these cases. Saying that you "aren't sure" is a bit rediculous. In all but the "them" sample, it's a very clear cut case. In "them" the sum of the high frequencies across the file are encoded more often in --aps than in --r3mix. There's more stability and accuracy in terms of quality in the --aps file.

QUOTE
To know wether R3mix or APS shows more HF content, a global spectrum analysis of the sample should be made, instead of a sonogram.


--r3mix may at times show higher peaks in the one sample, but remember that this is by .5khz at 19khz, which is, again, not going to be significant in any case compared to the artifacting shown in the --r3mix sample.

QUOTE
But I don't think that the RMS level of HF content means anything. Remember that those are nearly unaudible frequencies, therefore only yellow plots should be taken into account. Grey parts are surely completely inaudible. From this point of view, r3mix shows more HF content than APS in the "them" sample, and the other sample show no (audible) HF content at all.


Sorry, but I beg to differ. Having spent a large amount of time tuning LAME and at times using sonograms to determine the point of error, I can say with confidence that these frequencies you deem to be inaudible, are actually quite audible in some cases.

Have you ever heard of the artifact termed noise pumping? This is caused by a failure to encode enough (high frequency) background noise, usually in a quiet file. This is the type artifact you will get if you do not encode this to a high enough frequency, and from personal experience and that of many people on this board, --r3mix does not. This is at least partially due to the ATH in --r3mix being too high (which also leads to other artifacts such as ringing which is actually very rapid and short bursts of the "noise pumping" or "dropout" type problem).

Other than that, I find it a bit ludicrous that you would say that the --r3mix sample shows more high frequency content and that the problems would be inaudible. Fatboy, spahm, and many others show the exact same problems and as with them, they are certainly audible. Yes, this is on impulse samples, but the same effect induces different artifacts in other cases.

The point then remains, that --alt-preset standard encodes more high frequency content, and with higher accuracy, than --r3mix, especially on difficult samples.

QUOTE
But remember, graphs mean almost nothing. EG the HF part could in fact be some impulse content. In that case, the lack of HF content doesn't "muffle" the sound at all, but creates pre-echo instead.


True, but I never said anything about "muffling" at all, I only ever discussed high frequency content by itself. So then, just change the statement. "--r3mix shows high frequency pre/post-echo in addition to many other artifacts due to its failure to properly encode high frequency content in many cases".
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Posts in this topic
- Dibrom   a response to a growing rumor...   Feb 12 2002, 00:36
- - rc55   Dibrom, I'd say it'd be a good idea to keep this ...   Feb 12 2002, 00:52
- - Dibrom   QUOTE Originally posted by rc55 I'd say it'd be a...   Feb 12 2002, 01:03
- - ff123   It's a many-headed hydra. Just as soon as one can...   Feb 12 2002, 02:53
- - Dibrom   QUOTE Originally posted by ff123 It's a many-head...   Feb 12 2002, 06:03
- - mithrandir   The --alt-presets are some of the best improvement...   Feb 12 2002, 06:54
- - PatchWorKs   Well, sincerly i can't understand why LAME have so...   Feb 12 2002, 10:48
- - cadabra3   As a Psychologist (forgive me ahead of time); I se...   Feb 12 2002, 11:13
- - JohnV   QUOTE Originally posted by cadabra3 As a Psycholo...   Feb 12 2002, 13:47
- - brosselle   QUOTE Originally posted by ff123 I think the bes...   Feb 12 2002, 15:17
- - JohnV   Well, just read Roel's (r3mix's) comment about alt...   Feb 13 2002, 06:32
- - Dibrom   QUOTE Originally posted by JohnV Well, just read ...   Feb 13 2002, 08:22
- - Delirium   QUOTE [b]I've never really seen this verified, tha...   Feb 13 2002, 08:59
- - Gabriel   I think that an improvement for someone could be a...   Feb 13 2002, 09:23
- - Dibrom   Yes, nitpicking aside... it perhaps is possible (a...   Feb 13 2002, 09:40
- - cadabra3   JohnV- no disrespect intended- if you read a littl...   Feb 13 2002, 10:59
- - Pio2001   Roel didn't say he would never use APS, he was jus...   Feb 13 2002, 12:31
- - tangent   QUOTE Originally posted by Pio2001 Roel didn't sa...   Feb 13 2002, 14:08
- - JohnV   Also one thing to consider when comparing this sma...   Feb 13 2002, 16:02
- - Dibrom   QUOTE Originally posted by JohnV Also one thing t...   Feb 13 2002, 20:05
- - JohnV   Hey Dib, a bit OT. Could you make those pics a bit...   Feb 13 2002, 22:01
- - Dibrom   QUOTE Originally posted by JohnV Hey Dib, a bit O...   Feb 13 2002, 22:33
- - Gecko   That is some hard evidence, Dibrom! It may not exa...   Feb 13 2002, 23:00
- - Pio2001   QUOTE Originally posted by Gecko wonder how he ke...   Feb 13 2002, 23:16
- - Gecko   QUOTE Originally posted by Pio2001 It much easier...   Feb 13 2002, 23:47
- - Dibrom   Pio2001, It's a shame you didn't post your respon...   Feb 14 2002, 00:03
- - user   Hi, in r3mix and here people are referring to som...   Feb 14 2002, 00:45
- - JohnV   Uhm, user. About 7 messages above your post. Here...   Feb 14 2002, 01:05
- - JohnV   I'd say you really can't tell absolutely which one...   Feb 14 2002, 02:38
- - Pio2001   QUOTE Originally posted by Dibrom Pio2001, It's a...   Feb 14 2002, 13:09
- - JohnV   QUOTE Originally posted by Pio2001 To make it sho...   Feb 14 2002, 18:00
- - tangent   QUOTE Originally posted by Pio2001 To make it sh...   Feb 14 2002, 18:34
- - Gecko   Apart from discussing the point of the high cutoff...   Feb 14 2002, 19:52
- - Dibrom   QUOTE Originally posted by Pio2001 To make it sho...   Feb 14 2002, 21:01
- - fewtch   QUOTE Originally posted by tangent Really? Most o...   Feb 15 2002, 08:43
- - cd-rw.org   Just by showing up again Roel has already done mor...   Feb 15 2002, 10:28
- - Dibrom   QUOTE Originally posted by cd-rw.org Just by show...   Feb 15 2002, 11:29
- - johnicon   My $.02: I found the r3mix website in May of ...   Feb 15 2002, 13:25
- - brosselle   You know, I kind of liken this to the old vinyl LP...   Feb 15 2002, 14:46
- - fewtch   For some reason, I suspect Roel will "come around"...   Feb 15 2002, 15:28
- - user   Hi, during playing around with mp3gain, I found f...   Feb 15 2002, 23:08
- - Dibrom   QUOTE Originally posted by user 1.  maximize...   Feb 15 2002, 23:30
- - user   Thank you, now it is clear. yeah, as I spoke in s...   Feb 16 2002, 00:07


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