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292 discussions

end of files
by ff123 14 Feb '01

14 Feb '01

I don't know if it's a general problem or not, but I notice that MAD produces glitches in the output at the end of files. For instance, take a short .wav file and cut off the end with a sound editor so that there's still music playing at the end (not silence). Encode to mp3 and play with MAD. Then try the same thing with the decoder in Winamp 2.7x. I tried this test with MAD versions .12.3, .12.4, and .12.5. Maybe there's something about my PC or soundcard, I don't know. Also, I haven't checked recently, but at the time I was doing a MAD listening test on Usenet, I noticed that the MAD decoder (version .12.2) cut off about 30 milliseconds at the end compared with the Fraunhofer decoder in Winamp 2.666. Maybe the two problems are related. ff123

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Clipping - Some naive (?) questions
by D D 14 Feb '01

14 Feb '01

Greetings to all, I'm a new user to MAD and it's immediately become my standard for mp3 listening and decoding. The first thing that shook me when using Mad, was something that I never had encountered before, the mp3 clipping indicator. Low-bit distortion is one thing, but high-bit problems is surely a worse one, if not the worst! And when I witnessed Mad reports clipping even with files produced by the best encoders like Lame, this rang a red alert for me: are we constantly exposed to clipping distortion when using winamp's decoder or other decoding apps? Research in the web showed that there are people who claim that clipping is a well-known artifact of lossy mp3 compression. For me this is still a mystery, since I had the misconception (or is it true ?) that a well-established or even commercial encoder cannot possibly produce an mp3 that exceeds the 100% level. I am not familiar with the binary pcm structure of wav files, but I know it uses 16-bit numbers, so clipping is by the definition either the presence of a 17th bit (impossible) or the miscoding of a music level of 99% as 100% (which means that everything above 99% is clipped cause it's represented as a constant 100%). On the other hand, I understand that an encoded mp3 level of 99% is possible to be interpreted by a decoder as a level of 100%, which would mean that clipping is indeed possible to occur, but *only* when the file is badly decoded. For me two possibilities exist: a) The offending mp3 does not contain clipped samples but Mad misreports them (rather improbable, I do trust Mad's author programming skills) b) The offending mp3 does contain clipped samples which were produced by bad encoding (therefore Mad is correct) c) The offending mp3 does not contain clipped samples, but a decoder (either because of bad programming or because of the nature of mp3 lossy compression) *could* misinterpret them, so a decoder should take corrective action (i.e. attenuation like Mad does). I cannot easily find a way to produce convincing evidence as to which of the above is the case. At first sight one could propose: "just take an mp3 and decode it with a standard decoder and see if it contains clipped samples". However this is not good enough for me, for the following reason: If i use 10 standard decoders I'll get 10 wavs which will almost certainly differ. The next step would be to *visually* inspect the wavs for clipping, cause I do not think that any wav editor is capable of detecting and reporting (and possibly take action like Mad's attenuation) levels above 100% when opening a wav or importing an mp3 (am I wrong here?). In conclusion, to rephrase my (naive ?) questions: how is it in principle possible that Mad detects clipping, how does Mad do it and where exaclty is Mad detecting it: a) is clipping stored inside the mp3 file content? b) is it an artifact of decoding programs ? In addition, can you suggest another reliable means of verifying that an mp3 contain or not clipped content ? Excuse me for the lenghty post, but I think the issue I bring forward is an important one. For one, I would hate the idea of being forced to first normalise all my wav's to a safe e.g. 95% before encoding it, to just prevent the eventual clipping upon decoding.... Moreover if my worries are justified, we should definitely propose "response to mp3 clipping" as a very important criterium for the evaluation of mp3 decoders (and encoders ?) in that famous www page that does "objective" mp3 software comparisons. Best regards, Mits

4 3

MAD 0.12.5b available
by Rob Leslie 13 Feb '01

13 Feb '01

Hot on the heels of 0.12.4b, MAD 0.12.5b is now available with even more performance improvements. This version incorporates the long-awaited Huffman decoding optimization that performs requantization in the same step. Many thanks to Andre McCurdy for his help that led to this release. There are still a few more improvements to be made, but this probably represents the bulk of what can be optimized for significant gains. The source code release: ftp://ftp.mars.org/pub/mpeg/ The MAD plug-in for Winamp: http://www.mars.org/home/rob/proj/mpeg/mad-plugin/ The MAD home page: http://www.mars.org/home/rob/proj/mpeg/ Cheers, -- Rob Leslie rob(a)mars.org

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ID3v2 support?
by Vlad Indiukov 12 Feb '01

12 Feb '01

What about this stuff for winamp plugin?

2 1

resample problem..
by J.Saravanan 12 Feb '01

12 Feb '01

Hi All, I've compiled madplay for my arm target ( Its a CLPS7500 evaluation board). When I try to run the application I get the following error message... output: sample frequency 44100 Hz not availlable;closest 41666 Hz output: cannot resample 44100 Hz to 41666 Hz And the program quits. Can sombody tell me how to fix this problem. Thanks, _Saran_

2 1

MAD 0.12.4b available
by Rob Leslie 12 Feb '01

12 Feb '01

MAD 0.12.4b is now available. This version incorporates a number of performance improvements for all platforms. It also includes (untested) native fixed-point math support for the PowerPC platform, contributed by David Blythe. Since I've made some significant changes to the way the fixed-point math routines are maintained, I'd appreciate feedback from anyone using MAD on a PPC to make sure I haven't broken anything. Finally, this version changes the way mixed short blocks are handled in Layer III with respect to alias reduction, correcting another apparent ambiguity in ISO/IEC 11172-3. Since mixed blocks are rare (many encoders don't support them) this has until now gone unnoticed. Thanks to H.O. for reporting this. The source code release is here: ftp://ftp.mars.org/pub/mpeg/ Winamp users should notice improved performance in the MAD plug-in: http://www.mars.org/home/rob/proj/mpeg/mad-plugin/ The MAD home page is, of course: http://www.mars.org/home/rob/proj/mpeg/ Cheers, -- Rob Leslie rob(a)mars.org

3 3

New mailing list software
by Rob Leslie 01 Feb '01

01 Feb '01

This message serves both as a test and as an announcement of new mailing list software that is managing the mad-dev and mad-user mailing lists. If all went well, the transition should be pretty seamless. You can now manage your subscription from one of these pages: (mad-dev) http://www.mars.org/bin/mailman/listinfo/mad-dev (mad-user) http://www.mars.org/bin/mailman/listinfo/mad-user To make changes, first click the button to have your password mailed to you. As a bonus, both lists now have an online archive of past messages: (mad-dev) http://www.mars.org/mailman/public/mad-dev/ (mad-user) http://www.mars.org/mailman/public/mad-user/ Please let me know if you experience any problems. Cheers, -- Rob Leslie rob(a)mars.org

1 0

Comparing with old decoders
by Vlad Indiukov 30 Jan '01

30 Jan '01

Does anyone compare MAD quality with NAD and Appolo decoders? I mean objective comparing with frequency analysis etc, not sayings like "smooth and deep sound of decoder"

4 4

Why the strange drop-off in discussion?
by David Shin 30 Jan '01

30 Jan '01

At least 4 or 5 a day and then, boom, nothing. Am I still on the right mailing list?

1 0

l3dec 24-bit convert to wav
by ff123 28 Jan '01

28 Jan '01

I have written a short program to convert the 24-bit ASCII output of l3dec to .wav format, which can be read in by Cool Edit Pro. For fun only -- I don't see a useful purpose for it. http://fastforward.iwarp.com/convert.html ff123

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