I have an mp3 which I increased the volume with Amplify but now the voice is talking as if he did it with the loudspeaker of the phone (more or less to be understood) and wanted to know if it is possible to improve it with Audacity.
Excuse my poor english 
Thanks
It’s possible you have MP3 compression damage. All MP3 causes some sound damage and if you edit an MP3 in Audacity, the damage always gets worse.
Is this the kind of sound you have?
http://www.kozco.com/tech/WAV-MP3.wav
Koz
Perfect! The voice of my file is exactly like what I’ve shown you, the second part.
How can I fix?
The BIG problem with MP3 compression damage is that it can’t be fixed.
The MP3 format compresses audio to a smaller size by throwing away the “less important” audio data. The more data that is thrown away, the smaller the file size. This damage cannot be fixed because the missing data has gone forever. We always recommend that people use uncompressed audio formats (such as WAV) whenever possible so as to avoid this problem.
Ok, so it might work if I encode an mp3 to wav, modifies it and then re-encoding to MP3?
thanks.
No it absolutely isn’t the case.
You will be companding the MP3 compression damage. When you convert the MP3 to WAV, sure it becomes a “lossless” audio - but it still contains all the compression damage done in the initial MP3 compression - so the stuff that was thrown away in the compression is lost forever.
It’s a bit like taking a packet of chicken soup, adding the water and then reducing it to powder - and then making the “sup” again. Neither of 'em tastes like real chicken soup - but the latter one will definitely be the worst
WC
ok then how can I increase the volume of an mp3? Should I raise it because it is very very low.