FLAC File Size Grows!?!?

Using Audacity 2.1 installer on Windows 7

Hi guys, I’ve just started using Audacity to edit some FLAC files (2.0 and 5.1) and noticed something really strange: my file size grew (by 3MB for 2.0MB and by 26MB for 5.1) after saving at max compression compared to the original which is also done at max compression (level 8). To produce this, I would import my FLAC file and INSTANTLY export it as a FLAC file (level 8 compression). My file size is now larger than my original file created using eac3to. Even stranger is that when I decided to save the file as a .wav in Audacity (uncompressed) and have eac3to compress it to FLAC it ALSO was the same size as when Audacity does it, this confirmed that the compression method was not a factor. This leads me to believe that Audacity is somehow adding stuff to my file which it shouldn’t.

TL;DR Audacity is somehow adding data to my imports and thereby producing a larger file on export. This should be impossible for a lossless file and shouldn’t happen in general.

It’s lossless, but it’s still compressed. The compression efficiency can still go up and down.

Any help on what might be causing this and how to import/export a file while maintaining the import’s file size would be much appreciated!

Also remember, Audacity adds dither to every export, so the before and after are not identical.


Here’s the exception to the rule: If you have recorded in 16-bit and are only doing simple editing (cut, delete, paste, trim…) and not doing any processing (amplify, equalize, frequency filter…) then for highest accuracy dither can be set to “none”. In this case, because there are no 32-bit operations prior to export there is no benefit to using dither. Exporting a 16-bit track to 16-bit with dither set to “none” will be lossless. The same applies if exporting from a 24-bit track to an uncompressed 24-bit file format with dither disabled.

Thank you for the keyword I needed! I’ll have to redo all my work but I feel a lot better knowing this. My only remark would be is it better to edit in 24-bit and down convert after? Or will it not make any difference?


by 3MB for 2.0MB and by 26MB for 5.1)

That doesn’t tell us much since we don’t know how big the files were to start with…

If you convert from 16-bits to 24-bits, the file could increase by about 50% (although a FLAC file shouldn’t increase in size unless you also edit it in way that fills the extra 8-bits with information.)

If dithering is enabled it will add “information” (noise, actually) and that will usually increase the size of a FLAC. (You can disable dither.)

Dither being enabled was the issue. My only remaining question is is it better to do my edits in 24bit then convert down to 16bit or am i going to get the same results editing an already down converted file?

Audacity always works internally at 32-floating. So you always get two conversion no matter what. If you started out life with a 16-bit recording, you should probably just leave it there.

This is not like MP3 which can get very seriously worse with repeated exports.


Okay, it’s actually a 24bit just I’m converting down to 16bit before edit. I think I’ll let keep the 24bit then convert down after edit just to be safe…