The three formats
A WAV file stores every bit of audio your master contains, uncompressed. Nothing is thrown away and nothing is squeezed. It is the largest file of the three, and it is the closest thing to a raw, complete copy of your song.
A FLAC file is also complete. It uses lossless compression, which means it shrinks the file to roughly half the size of a WAV while keeping every sample intact. Unzip a FLAC and you get the exact audio back, bit for bit. Smaller file, identical sound.
An MP3 is different. It uses lossy compression, which throws away parts of the audio the format decides you are least likely to notice, then stores what remains in a much smaller file. A three minute song that is 30 MB as a WAV might be 3 MB as an MP3. Convenient for sharing, but some of the original is gone and you cannot get it back.
Lossless vs lossy, and why the order matters
This is the part that trips people up. Lossy compression is not reversible. Once an MP3 has discarded data, that data is gone, and every later step works from the smaller, incomplete version.
So the sequence matters. If you hand your distributor an MP3, the streaming platforms then re-encode that MP3 into their own formats. You end up compressing audio that was already compressed, stacking loss on top of loss. The high end gets brittle, busy sections smear, and quiet details vanish. Give them a lossless file instead and the platform encodes from a complete master, which is always cleaner.
What distributors actually want, and why they re-encode anyway
Most distributors (DistroKid, TuneCore, CD Baby, Amuse and the rest) ask for a 16-bit or 24-bit WAV at 44.1kHz. Many accept FLAC too. They want lossless because they are not the final destination. They are the middle step that delivers your song to dozens of platforms, and each platform encodes its own way.
Spotify uses Ogg Vorbis at a few bitrates. Apple Music uses AAC. YouTube has its own pipeline. They all start from whatever master your distributor passes along, so you want that starting point to be as complete as possible. Send lossless, and every platform gets a clean source to work from. That is also why loudness is worth getting right before you upload, since each platform normalizes differently.
The decision
WAV or FLAC goes to your distributor. Always. Pick WAV if you want the safest, most universally accepted file and do not mind the size. Pick FLAC if you want the same lossless quality in a smaller upload, and you have confirmed your distributor accepts it. Both are correct. WAV is simply the default nobody questions.
MP3 is for everything that is not a distributor. Sending a rough mix to your bandmates, posting a clip to Instagram, emailing a demo to a venue, dropping a track in a group chat. MP3 is small, plays everywhere, and is perfect when convenience beats fidelity. Just never let an MP3 be the file your release is built from.
Which Bandmixr export to grab for each destination
Bandmixr exports all three, so you do not have to convert anything yourself or guess at settings. Once your mix and master are done, you choose the format that fits where the file is going.
Grab the 44.1kHz / 24-bit WAV for your distributor. That is the upload that goes to DistroKid, TuneCore or whoever you use. If your distributor prefers FLAC or you want a smaller lossless file, the FLAC export is the same quality in less space.
Grab the MP3 for socials, demos and quick shares. It is the file you send when someone needs to hear the song now and does not care about the last few percent of fidelity.
Common mistakes worth avoiding
Uploading an MP3 master is the big one. It looks fine on your laptop, but the platform re-encodes it and the result gets noticeably worse. If lossless is an option, and on Bandmixr it always is, use it.
Watch the sample rate too. Distributors expect 44.1kHz, which is the standard for streaming and CD. Bandmixr exports at 44.1kHz, so this is handled for you, but if you are converting files from elsewhere, do not upload something at a mismatched rate and hope the platform sorts it out.
One more thing that lives next to format: loudness. The right format protects your audio, but the right master loudness decides how your song sits against everything else in a playlist.