I know that importing an mp3 file into audacity then exporting it again (with or without changes) alters audio quality. I was just wondering to what extent this was the case and how audible the change actually is. Thanks
It pretty much doubles. If you try to import and export an MP3 at the same bitrate and the original was already cutting it close, the output will be unusable.
There are two ways around this in Audacity. Export the new MP3 at a nosebleed high bitrate (360 or higher) or Export an uncompressed format, WAV, AIFF, etc.
That’s it.
If you have MP3 editing to do and it doesn’t involve intensive special effects – just cutting, then you can use one of the fine MP3 editors out there that don’t uncompress the original
https://forum.audacityteam.org/t/turning-an-mp3-into-multiple-files/17820/2
Most people want to use downloaded MP3 files as if they were master audio files ripe for editing, effects, and filters.
MP3s aren’t ripe.
Koz
Thanks much Koz,
So if I were to do everything I normally do (including using the mp3s in an audacity project) but export as WAV instead of mp3, the quality will not be affected?
That’s correct. WAV files can have problems, too, but those problems are mere piffles compared to MP3 damage. You can go back to MP3 if you need to, but you’ll need to do it at a very high bitrate, almost making it not worth it.
Broadcast Television Production, Music CD and PCM tracks on Movie DVDs are all WAV variations. Very good, very stable.
Koz
I believe Koz here meant to say 320 (kbps) and you can’t go higher than that…
The extent of mp3 compression damage depends mostly on the bitrates involved… If the original mp3 is at 320kbps it should have very little damage on it and you might not be able to tell the difference if you reencode it again at 320kbps (of course this will also depend on the sensitivity of one’s ears).
If the original mp3 is at 64kbps and you reencode it again at that same bitrate expect severe damage…
The kind of show and its intended target also might have some influence… If we’re talking about a recording of just some guy talking (with a narrower frequency spectrum), intended to be added to a low quality youtube video, well… a bit more damage probably won’t hurt much… If it’s a more complex music track intended to be played on a high-end hifi system, then the double mp3 compression will probably kill your show… (even just the first compression might do it by itself).
Thanks much for the help guys…
Also, when I import audio clips into my projects, they come in as 32 bit float. I am planning on just switching to WAV for exporting, but Im curious about this anyway. If I reencoded (exported) the project at a higher bit, would it fix the problem with mp3 damage?
AFAIK you can’t export mp3 in 32 bits.
I think you can export WAVs in 32 bits.
Audio CDs are 16 bits (stereo and 44.1 kHz).
Normal ears won’t be able to tell the difference between 16 bits and 32 bits.
mp3 is a lossy codec, that means it does damage in sake of compression and you can’t change that… mp3 compression will always do some damage no matter what… If you don’t want damage use FLAC or WAV (or any other lossless codec).
Damage on 320kbps mp3’s is very hard to detect… Lower bitrates will make more damage… the lower the bitrate the bigger the damage is.