Convert MP3 to FLAC

What FLAC can and can't do for an MP3

FLAC is lossless: it stores exactly the sound it is given. Given an MP3, it stores the sound as the MP3 plays it, missing detail and all. The FLAC sounds exactly like the MP3, no better and no worse.

It can't hide where it came from, either. MP3 encoders cut off the highest frequencies, and a spectrum view of the FLAC shows that missing top end plainly. Services and collectors that check for “fake lossless” files will spot it, so don't present a converted MP3 as a lossless original.

Think of the FLAC as the MP3 in a different box: useful when the box is what's required, and nothing more. The one real gain is that from here on, nothing else is lost: every copy and edit made from the FLAC stays exactly as good as it is now.

When it still makes sense

• A program or device demands FLAC, such as a player set up for a FLAC-only library, or a tool that won't import MP3.
• An upload form only takes lossless files and the MP3 is all you have. Say so if you're asked about the source.
• Editing in several rounds. Decode once to FLAC (or WAV), then edit and save as often as you like: each save stays lossless, where saving as MP3 every time would lose a little more each round.
• Keeping a one-off recording safe from further lossy steps, when it only exists as an MP3.

If you do have a better source, a CD or a WAV, make the FLAC from that instead: WAV to FLAC. That FLAC is the real lossless copy, with all the detail the MP3 never had.

Whatever the reason, label converted files clearly, for instance by keeping “from MP3” in the folder name, so nobody mistakes them for true lossless copies later, including you, years from now.

Settings and size

An MP3 decodes to ordinary 16-bit sound at its own sample rate, so Octoolo writes a 16-bit FLAC at the same rate. You can choose 24-bit under More settings, and some tools ask for it, but it adds nothing except size. The sample rate is never raised on its own either: a 44.1 kHz MP3 gives a 44.1 kHz FLAC, and choosing a higher rate would only make a bigger file with the same sound.

The FLAC will be several times bigger than the MP3, because it stores the decoded sound in full. CD-quality FLAC typically needs 5 to 7 MB for each minute, while a 128 kbps MP3 needs 1 MB and a 320 kbps one 2.4 MB. A 4 GB folder of MP3s can become anywhere from about 8 to 28 GB of FLAC, depending on the MP3s' bit rate, so check your spare disk space before converting a whole library.

Tags and covers

Title, artist, album and the embedded cover picture all go into the FLAC, so the files sort and look the same in your player. Each FLAC keeps its MP3's name and sits beside the original, and the MP3 is never touched, so you can delete whichever copy you don't need afterward.

If you'll later need MP3s again, go back to those originals rather than converting the FLACs: an MP3 made from the FLAC would be a second-generation copy of the first, with one more round of loss for no reason. Keeping both side by side for a while costs only disk space. Cover pictures are copied exactly as they are in the MP3, neither shrunk nor re-saved, so artwork looks the same in both. Like any FLAC tags, they can be edited later in your music player or a tag editor.