I work with audacity 2.1.1 to edit my mp3 file. my file are very small (0.2 - 0.4 sec). After I save the file to mp3 format audacity add automatically silence at the beginning of the file, something like 0.05 sec of silence.
How can I remove completely the silence at the beginning of the file?
That’s a characteristic of the MP3 format ([u]LAME Technical FAQ[/u]).
You can use a different format or there are a few workarounds for “gapless MP3 playback” (which you can research).
FYI- Audacity (and all “normal” audio editors) has to decompress the MP3 when you open it. MP3 is lossy compression so if you re-export to MP3 (or other lossy format) you are going through a 2nd lossy compression step. Ideally, you should work with lossless formats and compress ONCE as the LAST step. If you don’t have a lossless original, try to minimize the number of times you compress. Or, there are special purpose MP3 editors programs such as [u]MP3directCut[/u] that can edit MP3s without decompressing. (That doesn’t solve the added-silence issue.)