Vocal reduction and isolation

Dear friends :
When applying the Vocal Reduction and Isolation is better to have the original recorded file or it can be used mp3 files , to get the same final result ?

Vocal reduction and isolation can be used on MP3s, but generally it is better to use a high quality WAV for best results.

MP3s have cleverly hidden compression distortion which can affect tools, filters, effects and corrections in unpredictable ways.

Even if you do get all the corrections to work perfectly, if you make a new MP3 in Audacity, the compression damage could as much as double. There is no opening a 128 quality MP3 and export a 128 quality MP3. You can minimize the damage increase by exporting a very high quality MP3 (320) or freeze the damage in place by exporting one of the uncompressed formats such as WAV, AIFF or FLAC.

It’s never a good idea to do production in MP3.