Using Audacity to amplify a track

[Trebor]

Is there a way to import an mp3 file, let's say it's 320 kbps, amplify it and then export it as a 320 kbps file without adding any more compression?

To avoid more compression damage, need lossless MP3 editor instead of Audacity ...
e.g ... https://en.wikipedia.org/wiki/Mp3DirectCut

[kozikowski]

What he said.

The problem is the work is not MP3 while it's inside Audacity. It's in Audacity's super high quality internal format to avoid sound damage from effects, filters, and corrections. That's pretty harmless going in, but then most people want to make the show back into MP3. That means 320 compressing a show that already has 320 compression damage. There is no filtering out that damage once you have it.

This is the exact reason we tell the audiobook people their Edit Master should be a perfect quaity WAV file and not the MP3 they submit for publication.

What's the show that has 320 MP3 compression? That's pretty unusual.

The pure MP3 editors are usually pretty limited. Cutting and editing is usually OK, but there can be some serious limits to volume changes. Special Effects are usually forbidden. MP3 gets its small files by shuffling audio tones within the show and sometimes deleting some—and then cleverly hiding what it did. If you mess with the tones or their relationships, the "cleverly hiding" part may go away.

Make sure you know what bad MP3 compression sounds like. Also note you're going to get "Human Volume" sound damage, too. Audio shows sound much better louder—even though the quality didn't actually change. This gives you the music store which makes the player they went you to buy louder than the others.

Koz

[DVDdoug]

I ask because I occasionally encounter music files that have room to bring it up.

Without decoding, MP3s can be adjusted in 1.5dB steps. If you normalize with MP3directCut you'll end-up with peaks between 0dB and -1.5dB.

MP3 can actually go over 0dB without clipping but you'll clip your DAC if you play it at "full digital volume". It's not unusual to find MP3s that go slightly over 0dB because if you convert a normalized WAV to MP3 some peaks get higher.

I don't really want to create a file 5 times larger either.

The bitrate is directly related to file size - There are 8 bits in a byte so 320kilobits per second is 40 kilobytes per second (plus any embedded artwork). CDs have a bitrate of 1411kbps (44.1kHz x 2 channels x 16-bits) so that's about 5 times the size.

amplify it and then export it as a 320 kbps file without adding any more compression?

You might be OK with 2 generations of compression but even without more compression damage does accumulate and MP3 is one of the worst formats for accumulated damage. Nine different codecs 100-pass recompression test