WAV, AIFF, FLAC or MP3: what to actually play out

Play 320 kbps MP3 or AIFF out, and keep the lossless file at home. On a club system, through a limiter, in a room full of people, nobody is picking a properly encoded 320 out from the WAV it was made from, and the MP3 takes a quarter of the space on the stick and carries all your tags. If you want lossless on the stick, AIFF is the one to use, because it tags like an MP3 and every CDJ plays it. WAV plays everywhere but its tagging is the weakest of the four. FLAC is the best archive format and the worst booth format, because older CDJs will not read it.

That is the answer. The rest of this piece is the reasoning, so you can disagree with it on purpose rather than by accident.

What each format is

WAV is uncompressed audio in a container that Microsoft and IBM defined in 1991. The samples are stored as they came off the converter, so a WAV is the master, byte for byte, and nothing has been thrown away. It is the format most stores deliver lossless in.

AIFF is Apple’s equivalent, from 1988. The audio inside is identical to WAV, uncompressed PCM, and the file is the same size. The difference is the container, and specifically that AIFF has a proper, widely supported place to put ID3 tags, which is the thing WAV lacks.

FLAC is lossless compression. The audio is packed down like a zip file and unpacks to the exact original when played. Nothing is lost, the file is a little over half the size of the WAV, and it has good tagging. It is the format to archive in.

MP3 is lossy. The encoder removes the parts of the audio it decides you cannot hear, and the higher the bitrate, the less it removes. 320 kbps is the ceiling for MP3 and the standard for DJ use. A 128 kbps MP3, the sort that came off a file sharing network in 2004, is a different thing, and yes, you can hear that one.

Lossless against lossy on a club system

The argument for lossless in the booth is that you can hear the difference. On a decent home system in a quiet room, with the original next to the MP3, some people can, sometimes, on some material, and mostly at bitrates below 320. On a club system the comparison is not happening in a quiet room. It is happening through a compressor and a limiter, in a space with a reverb time measured in seconds, over a crowd, at a level where the loudspeakers are the thing adding distortion.

What people actually hear when they think they hear the codec is usually the master. A badly mastered WAV sounds worse than a well mastered MP3 in any room. What they also hear is level, because the louder of two files sounds better on a quick comparison.

So the honest position is this. 320 kbps MP3 from a lossless source is transparent for nearly everyone in nearly every room. Lossless costs you nothing except space and, in the case of WAV, tags. Pick on those terms, not on a fear that the crowd can hear the encoder.

Where quality does matter is upstream. Never encode an MP3 from another MP3. Every generation of lossy encoding throws more away, and a 320 made from a 192 is a 192 with a bigger number on it. Convert from the lossless file, once.

Tags, and why WAV is the problem

DJ software lives on tags. Artist, title, BPM, key, artwork, and the comment field a lot of DJs use for their own notes. MP3, AIFF and FLAC all have a well defined place for that data, and Rekordbox, Serato and Traktor all read and write it.

WAV does not, or not reliably. The original WAV specification has a small info chunk that holds artist and title and not much else. Software vendors have bolted ID3 tags onto WAV since, but not all of them did it the same way and not all of them read what the others wrote. The practical result is that a WAV analysed in one program can turn up in another with no key, no artwork and a title read from the filename. If your library is in one piece of software and stays there, it mostly works. The moment you move between programs, or hand a stick to someone else, WAV tags are the thing that goes missing.

AIFF fixes this. Same audio, same size, and an ID3 chunk that everything reads. If you want lossless on the stick and you are on Pioneer gear, AIFF is the answer, and it is the reason a lot of DJs who buy WAV convert it to AIFF before it goes anywhere near a CDJ.

FLAC tags well, using its own system rather than ID3, and modern software reads it fine. The problem with FLAC is not tags.

FLAC and the CDJs that will not play it

The CDJ-2000NXS2, the CDJ-3000 and the current XDJs play FLAC. The original CDJ-2000, the CDJ-2000 nexus and everything older do not, and there are a great many of those still in booths. Turn up with a stick of FLAC at a venue with a pair of first-generation nexus decks and you are not playing.

Serato only added FLAC relatively recently, so older installs and some older controllers have the same problem. Traktor and Rekordbox have read it for years.

The other compatibility trap is sample rate. CDJs are happy with 44.1 and 48 kHz at 16 or 24 bit. A 96 kHz WAV from a mastering engineer is a file that some decks refuse outright. Keep the stick at 44.1 or 48.

What it costs you in space

Approximate sizes for a six-minute stereo track. These vary with the material and the encoder, so treat them as a guide rather than a measurement.

Format	Approximate size, 6 minutes	Approximate tracks on a 128 GB stick
MP3, 320 kbps	14 MB	9,000
FLAC, 16-bit 44.1 kHz	35 to 40 MB	3,300
WAV or AIFF, 16-bit 44.1 kHz	63 MB	2,000
WAV or AIFF, 24-bit 44.1 kHz	95 MB	1,300

The stick is not the only cost. A CDJ has to read the file before it plays, and a 95 MB file from a slow USB stick takes noticeably longer than a 14 MB one, which is the difference between a track that is ready when you need it and a loading bar while the outgoing track runs out. Rekordbox export takes longer in proportion, and so does the backup you are hopefully running.

The setup that works

Keep two copies. The lossless file, WAV or FLAC, is the master. It lives on a drive at home, backed up, and it is the one you go back to if you ever need to re-encode, re-edit or re-master. The playing copy is either a 320 kbps MP3 or an AIFF, tagged, analysed, and on the stick.

For most people, the MP3 is the right playing copy. It plays on every deck and every version of every piece of software, it holds tags properly, it loads quickly, and it fits a whole crate on one stick with room to spare. If you have the space and prefer lossless in the booth, use AIFF and accept that the stick fills up four times faster.

Whatever you do, do not let the archive and the playing copy drift. Convert once, from the master, and let the converter carry the tags across so that BPM and key do not have to be analysed a second time.

ID Crate’s converter is built for exactly that step. Drop WAV, AIFF or FLAC files in, up to 300 MB each, which covers a ten-minute 24-bit 96 kHz WAV, and it returns 320 kbps MP3 with artist, title, album, BPM, key and artwork written as ID3v2.3 tags, the dialect that Rekordbox, Serato and Traktor all read without argument. The input and output are deleted as soon as the download completes. Free accounts get 3 files a month, and Pro and Pro Plus are unlimited within fair use.

The short version

Lossless at home, 320 or AIFF on the stick, 44.1 or 48 kHz, tags intact. Never encode from an MP3. Do not take FLAC to a venue unless you know the decks. And stop worrying that the crowd can hear the codec, because they cannot, and they would rather you spent the effort on the tracklist.