MP3 encoding removes silence?

[cornutt]

Not really a Metro question, but I figured people here might know...

Why is it that if I insert an area of silence at the beginning of an audio track, and then export that track to MP3 format (or export to AIFF and then convert it with iTunes; it does the same thing), it deletes the silence? I'm trying to put together some tracks for a ballroom dance exhibition, which are going to be played with iTunes. We want to be able to hit "start" at the beginning of the show and then not touch it until the end of the show. This means that I have to insert some amount of silence at the beginning of each track, so that the dancers get on and off the floor, and the time is different for each track according to the staging.

To make it work, what I've been doing is recording a period of "analog silence" (i.e., the output from the mixer with the master fader turned down to zero), and then trimming that to the needed length. That works, but it's a pain to remember to do it every time I have to put together a track. I have also noticed, in another song that I did in two "movements", that when I inserted a silence period in between the movements and then converted it to MP3, that my MP3 player reproduces it as a period of random pops and noises with a random length. Anyone know what it is about MP3 that causes this behavior?

[Jerm]

The short answer is I do not know for sure.

I believe that if iTunes or any other application is inserting pops where silence was when converting AIF to MP3 then that should be considered a bug.

Can your MP3 player play Ogg-Vorbis format or MP4?

[cornutt]

I believe that if iTunes or any other application is inserting pops where silence was when converting AIF to MP3 then that should be considered a bug.

I'm pretty sure that iTunes isn't inserting the noise. When I convert the track to MP3 directly from Metro by using Export with Quicktime, the same thing happens. (Of course, it's entirely possible that it's actually using the same code.) And if I load the MP3 into a friend's iPod, it doesn't have a problem with the mid-song inserted silence. However, the silence inserted at the start of the track is still gone. And if I re-import the MP3 back into Metro, I observe the same thing: the mid-song silence is OK, and the start-of-song silence is totally gone. It's almost like there is some non-standard way of encoding periods of total digital silence (all zero words) that different MP3 encoders and decoders treat differently.

My MP3 player unfortunately doesn't do any other formats (other than Red Book).

[Jerm]

Wow... I did not know that it was possible to use Quicktime to export MP3. How do I get Metro to do that? Lame?

[Scoot]

I cannot reproduce this problem.

Firstly I inserted time at the start of a song and exported it out as an AIFF.
Dropped it onto itunes and the song started 8 seconds late.

Then I added the same amount of silence (a few bars), saved it off again and the song started 16 seconds late in itunes.


So I know the AIFF's are behaving cause I checked them in QT player.

I then converted them to MP3 within itunes and they are still the same.
Even in QT player.

I'm in OSX 10.2.6 and QT 6.4
My version of itunes is older - 4.0.

Could it be quicktime?


scoot.

[Jerm]

Please see my recent post regarding direct support for MP3 in Metro. Perhaps cornutt is referring to this. If that is the case then it is very likely that there is a problem in the encoder whereby it deletes silence at the beginning of the audio file because as I mention in the other post, there is a problem when outputting mono files to the encoder.

[cornutt]

Please see my recent post regarding direct support for MP3 in Metro. Perhaps cornutt is referring to this. If that is the case then it is very likely that there is a problem in the encoder whereby it deletes silence at the beginning of the audio file because as I mention in the other post, there is a problem when outputting mono files to the encoder.

Could be, although the tracks I'm exporting are stereo. I'm still running 10.2.3, although I have the Panther update disk in my hot little hands right now. As soon as I find time, I'll run the upgrade and download the latest Metro version and try it again.