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Topic: Loud pop at start of MP3 files (Read 4185 times) previous topic - next topic
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Loud pop at start of MP3 files

Hello,

I have some MP3 files that were encoded from WAV with LAME 3.97. Near the start (around 9000 samples in), some of the files have a loud pop when played or decoded to WAV with Foobar. The same is true when played or decoded to WAV with iTunes.

However, the original WAV that the MP3 came from is clean (no pops), and when I play the "bad" MP3 file in WinAmp, MediaMonkey, Windows Media Player, and VLC, the pop is not there. I have even decoded the MP3 to Wav using RazorLame, and the resulting wav file is fine, i.e. no audible (or visible in Wav editor) pops.

I could just write this off as a "bad" MP3 file (corrupt for some reason), and just re-encode from the original wav file, which is fine.

But what bugs me is WHY does this audible glitch show up only in FooBar and iTunes? If the MP3 was bad, wouldn't all players exhibit this effect?

I have samples - the original file is in FLAC, and also I have the MP3 file that has the glitch in it - only when played or decoded with FooBar or iTunes. This is true on multiple computers that I have tried it on.

Is the glitch always there, due to an MP3 encoding error, and some decoders suppress it while others do not? The glitch looks like about 1600 samples of "all digital ones", i.e. each sample has a value of FFFF in hex. That is what it looks like in a wav editor, when looking at the wav from the decoded MP3 that was decoded with foobar or iTunes.

MP3 decoded to WAV with RazorLame and also when the MP3 is played with other players, the glitch is not there!

Thanks!

Loud pop at start of MP3 files

Reply #1 –
Quote from: Straightbourbon on
But what bugs me is WHY does this audible glitch show up only in FooBar and iTunes? If the MP3 was bad, wouldn't all players exhibit this effect?

I have samples - the original file is in FLAC, and also I have the MP3 file that has the glitch in it - only when played or decoded with FooBar or iTunes. This is true on multiple computers that I have tried it on.


You are allowed to post clips up to 30 seconds long in the Uploads Forum. I'd suggest using mp3directCut to extract the first 5 seconds or so without re-encoding - possibly less than 1 second would be fine too. Perhaps someone can diagnose the problem from the file.
Dynamic – the artist formerly known as DickD

Loud pop at start of MP3 files

Reply #2 –
I can try and post a sample soon.

In the meantime, it looks like it has something to do with tagging with Picard in OSX. I am not sure if it is JUST the tagging, or if it is a combination of tagging first, then importing into iTunes.

http://forums.musicbrainz.org/viewtopic.php?id=1786

Loud pop at start of MP3 files

Reply #3 –
This is just something to try....

Do a google for MP3DirectCut and try opening one of the problem MP3s with it. I had a similar problem with some MP3s producing the same loud noise when I played them with my MP3 player, although I think most of them played okay with foobar. When you open the MP3 you may see a section at the beginning which looks like a big spike. I found that by using MP3DirectCut to remove that little bit of the MP3 and then re-saving the file the problem would be fixed.

Do you by any chance use MPGain on your MP3s?

It's not that I know what the cause is, but from what I read I'm guessing it's something to do with the level the encoder tells the MP3 player to play at when there's nothing but silence, and changing that level with a program such as MP3Gain can produce odd results. Maybe even just adding replaygain tags can have the same effect.

From what I understand each frame of an MP3 includes volume data, which is how MP3Gain changes the level of an MP3 without effecting the quality. It simply adjusts the volume information. I suspect that maybe a frame of an MP3 can have corrupt level data, and I'm sure I've had MP3s where it's missing. Maybe that happens due to tagging or something similar, I don't really know, but I guess some players cope with bad volume values in a frame better than others.

As I said, I'm just guessing and most of the above may be completely inaccurate, but I do know that by opening the MP3s with Mp3DirectCut I could see the bit at the start of the MP3 which needed to go. I also had some MP3s which produced a similar loud click at the end which I could remove, and by using MP3DirectCut you're not decoding and then re-encoding the MP3 so there's no quality loss.
I often use it for cleaning the silence at the beginning and end of an MP3 anyway, or for fixing overly long fade outs.... that sort of thing.

Loud pop at start of MP3 files

Reply #4 –
I used Mp3DirectCut to create a 25 second clip of the file. The glitch is at the very beginning - within the 1st second or two.

When I play this in foobar or iTunes, I hear the glitch. When I play in Winamp, Media Monkey, VLC or windows media player, the glitch is inaudible.

Now how do I upload / attach the audio clip?

Loud pop at start of MP3 files

Reply #7 –
LAME --decode says:
Code: [Select]
Frame#     7/1003   224 kbps  L  R   mpg123: Can't rewind stream by 106 bits!

It looks like the file is corrupted somehow.
 

Loud pop at start of MP3 files

Reply #8 –
Could you upload a clip of the WAV file that triggers the bug?