I have thousands of MP3 files mostly ripped at 128 bit rate. I want to reduce the size of them all, but am concerned about losing a ton of audio quality. I’ve seen a mixture of opinions on whether it can be done using Audacity, but the posts are mostly old, so I’d like to see if anyone has had any luck doing it lately. Any luck?
It’s nothing to do with “luck”. If you re-encode an MP3 at any bit rate, even the “Insane” preset of 320 kbps Constant Bit Rate, you will lose more quality. Re-encoding medium quality 128 kbps files at a lower bit rate will likely degrade them significantly.
If you must re-encode the files at a low bit rate, I suggest using Variable Bit Rate at Quality 8 or 9, and not Constant Bit Rate. You may even be able to use Variable Quality 7 and get a decent size reduction if the content of the files is not too demanding to encode. That is the benefit of using Variable Bit Rate, using less bits for easy-to-encode material (and more bits for more demanding material).
You’ll just have to experiment… Whatever is “too much quality loss” is up to your ears & your taste. (Many people would consider 128kbps not good enough, or just-barely good enough.)
Whenever you encode-or re-encode, you loose quality. In theory, you’ll loose quality if you re-encode to a higher bitrate (bigger files) because you’ve gone through the lossy compression process twice.
If you have the CDs, re-ripping from the lossless original to something like 96kbps will give you better results than transcoding from 128 to 96kbps.
For best results use Joint Stereo, and use ABR (average bitrate) or VBR (variable bitrate). ABR uses a higher bitrate for parts of your file that need it, and a lower bitrate for easier to compress parts. VBR targets a quality-level rather than a specific bitrate, so the file-size is not as predictable.
I’ve seen a mixture of opinions on whether it can be done using Audacity,
With the optional LAME MP3 encoder you can use Audacity to re-encode to whatever bitrate/quality you want, but re-encoding is generally not recommended (if you can avoid it). The quality you get depends on the MP3 encoder (LAME) and has nothing to do with Audacity.
If you want to edit your files, there are some special-purpose MP3 editors that can do limited editing without de-compressing/re-compressing. All “normal” audio editors requre the audio to be de-compressed before editing, which means a 2nd lossy compression step if you re-save (export) in a lossy format. This is why you sometimes read, “Don’t use Audacity to edit MP3s.”
If you are getting acceptable quality and you decide to go-ahead re-encode a bunch of files, it would be easier to use something [u]TAudioConverter[/u] instead of an audio editor. Once TAudioConverter is set-up with the output format of your choice, you can just drag-in a bunch of files and “click”.
This is the origin of the phrase “Never do production in MP3.” The first time an MP3 (or most other compressed file type) is made it creates the original show plus some cleverly hidden sound damage. The second time you do it, the software compresses the show plus the damage. Now the damage is much harder to hide. If you’re lucky, the damage only doubles.