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lame mp3's not completely gapless on 5G ipod
pabouk:
Thank you for the information! In fact I did not test the problem with pops thoroughly and it could be probably caused by the CD ripper because I used foobar2000 for CD ripping for the first time. I will do some tests (with and without compression) and post the results.
saratoga:
--- Quote from: preglow on September 11, 2006, 11:10:07 AM ---
Of course I have, I did these tests back when coding and validating Rockbox' gapless MP3 support.
--- End quote ---
Haha sorry, was distracted and didn't realize who I was quoting.
--- Quote from: preglow on September 11, 2006, 11:10:07 AM ---The problem stems from the fact that the encoder has to MDCT transform an incomplete frame of data, which has been padded with arbitrary values that should contain samples from the next track, but which don't, since the encoder encodes each track seperately when not in --nogap mode. When the two tracks are spliced together, this might cause phase discontinuities at the track change point, and this might be audible in rare cases. This will/should never happen with --nogap since complete frames are always coded, thanks to the encoder's knowledge about all tracks belonging to a gapless sequence.
--- End quote ---
Ugh. Heres where the limitations of my DSP knowledge come into play. It was my understanding that zero padding an MDCT results in no phase or magnitude distortion, but rather simply different points along the same (interpolated) curve. It seems to me that since I believe phase is not altered, and since the decoder can then trim off the excess samples, you should get essentially the same result.
However, I am not very familar with MP3 encoding.
Jag86:
Hi! I'm new in this forum, but I use RockBox since it was ported for my iPod model, a 2nd generation iPod mini. It's really a great OS for me, because it has a lot of functions that original OS doesn't have. One of the most important feature is the gapless playback, because I hate to hear those gaps between those songs which was made to play smoothly (such as lives or Pink Floyd creations).
However, the last bleeding edge releases of RockBox have a strange problem: if I play, for example, The Dark Side Of The Moon, the first four or five tracks play in a gapless way, but the remaining tracks don't play smoothly, there are noticeable gaps between them. One thing I noticed is that, if I start to play the same album from those last tracks, they play perfectly gapless.
I'm sure all of my mp3s have the extra-header (delay+padding) of Lame, because I verified with foobar2000 that they play gapless.
It seems a problem of a certain buffer, but I'm not into programming of RockBox.
I've got version 060828-1343 installed. I'm sorry if the post is so long :-[ , but I hope you can help me.
PS to the devs: continue in this way, you rock! ;)
lalittle:
--- Quote from: Jag86 on September 12, 2006, 06:58:20 AM ---if I play, for example, The Dark Side Of The Moon, the first four or five tracks play in a gapless way, but the remaining tracks don't play smoothly, there are noticeable gaps between them. One thing I noticed is that, if I start to play the same album from those last tracks, they play perfectly gapless.
--- End quote ---
Are you playing the album all the way through -- i.e. you're not just jumping to the next song to see if it's gapless, are you? The Rockbox software seems to need time to load songs into memory, so if you try to play the "next" song too soon, it won't be gapless.
Assuming you ARE letting the album play, I'm not sure why it would stop being gapless after a few tracks. It's NOT a problem with the encoding since they do play gapless in certain situations, so there's definitely something else going on. It looks like your build is from the end of August, however, so the first thing I'd try would be to update to the latest daily build and see if you still get this behavior. They're constantly changing/fixing things in Rockbox, so it's possible that whatever the problem was, it has since been taken care of.
Please post back to tell us what happened,
Larry
Jag86:
Hi Larry! First of all, thank you very much for your answer! ;)
Yes, I let play the album all the way through, because I wondered that Rockbox needs a little time to pre-load the next song. Honestly, I found this situation very strange! A funny thing is that when I try to play the "bad" tracks directly from them, without the previous ones, and I press+hold the skip button in order to do a fast-forward to the next song, everything plays fine! So, Rockbox is better than I thought!
I will try to install the latest daily build and tomorrow I'll post again to say if everything it's ok or not. ;)
PS: I forgot to say that I don't use any kind of equalizer or heavy WPS, just to be sure that iPod's CPU is not extra-loaded.
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