With news this week that Apple wants to make "24-bit" files available through iTunes, we thought it would be a good time to revisit the music formats that are out there and look at what they mean for digital DJs.
As a digital DJ, it pays to know your audio formats: Not only should you be aware of the different audio formats that exist, so you recognise them when you come across them, but also you should know when the use of each of the formats is appropriate and when it is to be avoided. Let's look a little closer...
Lossless vs lossy audio
This is the first distinction to make. Lossy audio is easily the most common of the types, basically because the ubiquitous MP3 is "lossy". This means that the audio you play has got bits missing from it, due to having been altered to make the file smaller. The algorithms that lossy formats use try and remove parts of the music where it doesn't matter so much - but the smaller the file is compressed to with these formats, the more trashed it becomes.
Lossless, meanwhile, is audio recorded without any musical data removed. These files come in two types - compressed and uncompressed. Compressed lossless audio has had inaudible changes made to reduce file size - they're typically not as small as lossy files, but the changes are enough to make a big difference to size nonetheless. Uncompressed lossless files are simply straight recordings of the original, with nothing done to them. The trade-off with these is that they take up much more room and are also harder to move around because of their size.
(By the way, there's a distinction to be drawn between "containers" and "formats", as anyone who's ever dabble with .avi video files and codecs can tell you! With audio, you don't really need to know about this but if you're interested, there a lot of dry depth on this Wikipedia page).
Let's take each in turn...
1. Lossy formats
The MP3 is easily the most widespread of the lossy formats. Some DJs refuse to use MP3s at all, saying even the best of them sound bad compared to lossless audio. Others are happy to, enjoying the convenience of their size, the fact that they have great metadata (album art, file information etc), and the fact that they're easily the most popular format.
MP3s at 320kbps are generally accepted as pretty indistinguishable from CD sound quality, 256kbps isn't far off. Personally, depending on the source material, I occasionally play at 192kbps, but never any lower. When you're ripping CDs you can specify the bitrate (more below), and you can buy 320kbps MP3s from web stores too.
AAC, or Advanced Audio Coding, is a relative of MP3 - only newer, and supposedly better. It is the native lossy format of Apple's iTunes, iPod, iPad etc. It usually has the file extension .m4a, and you'll see it if you buy from the iTunes store, for instance.
Because AAC does better at lower bitrates than MP3, to my ears 256kbps AAC files sound as good as 320kbps MP3s, so that's a good rule of thumb if you want to use AAC files. DJ software supports them, but there's no good reason to use them if you can avoid it; they're never going to win the battle with MP3 and it's just one extra format to have in your collection.
Basically WMA and OGG. Microsoft's proprietary Windows Media Player format (WMA) often has compatibility issues with players. If for some reason you're using Windows Media Player to organise your music, you can tell it to use MP3 instead, which is what I recommend you do. You may also come across OGG (or OGG Vorbis), but this is very uncommon for audio files.
2. Lossless formats
Taking the .wav extension, this is the most widely accepted - indeed, pretty universal - lossless, uncompressed format. Results are excellent and some DJs swear by only using .wav files. These files don't usually have any room for metadata though, and although a version of WAVE exists called Broadcast Wave (BWF) that allows metadata to be added, to my knowledge this isn't picked up by any DJ software. Thus if you decide you can't live with 320kbps MP3s and want to use WAVE files exclusively, you're going to have to be very organised with your music to survive without metadata.
Basically Apple's WAVE (.wav is actually a Microsoft format). Same losslessness, same professional-quality sound and the same limitations. Be aware that they're not as universally playable as WAVE files once you get away from Macs.
Unlike the two formats above, FLAC files are compressed, usually to about half the size of the equivalent WAV. With no loss at all in quality from the original and the ability to add cover art and metadata, plus support from most DJ software, FLAC files are popular with a minority of DJs, but they aren't compatible with iTunes without some hacking.
This works natively with all Apple hardware and software, but support is patchy in DJ software. (It has the .m4a extension like AAC).
DJ best practice
If you're a modern DJ, getting music from your own rips, the internet, downloads, friends who dabble in production, your own re-edits etc, you'll probably end up with any number of audio formats. It's worth your while to try and simplify things. We recommend sticking to MP3s at 320kbps for performance, and WAVs for when you're working on music - creating music, re-editing etc. (This is especially important when working with Ableton Live, for instance, as it can't use MP3s at all.)
That way, you have the same type of metadata going on with your performance files, you can throw sets together and put them on your iPod or MP3 player to learn your tunes, you can easily shuffle, order and make playlists with them in iTunes, and so on. Also, programs like Platinum Notes, Mixed in Key and MP3Gain, all of which you may choose to use at some point, will all give you the most predictable results if you give them all your music in the same file format to work with - otherwise you may find songs being skipped, metadata not being written correctly and so on.
If you use iTunes to organise your music library (and we strongly suggest that you do), you can set it up to prefer 320kbps MP3s (go to Preferences > General > Import Settings, then select "Import Using" and set it to "MP3 Encoder", and under "Setting", choose "Custom" and select "320kbps"), then it will do all your rips to 320kbps MP.
You can right-click on any file or files in iTunes and choose "Create MP3 version" to make a 320kbps MP3 of the song/s, but be aware that this works best with WAVEs or other high-quality audio - no point re-encoding MP3s at 128, 160, 192 or 256 kbps as 320kbps and expecting them to sound great, as you can't return musical information that's already been removed from them. Best just to leave them as they are.
However, there is an argument for converting (or "transcoding") 256kbps AACs as 320kbps MP3s if you're having issues with your DJ software / Mixed in Key etc and metadata, and just to keep things tidy. My advice is, as ever, to use your ears and compare versions - listening carefully on very good headphones will give you some impression of what your transcoded MP3s will sound like when you roll up at a club.
So what about 24-bit then?
We still haven't answered the question you might have asked on readingour opening sentence, on the word from Apple at wanting to offer "24-bit" files via iTunes. 24-bit refers to the resolution of the digital file. Digital music is basically a load of 1s and 0s, and 24-bit means every time a slice of the tune is sampled, it is represented with 24 1s and 0s, as against 16-bit, which is... well, you guessed. More 1s and 0s = better sound quality.
It only comes into play with uncompressed, lossless audio (WAVE and AIFF), which when ripping or recording, you can choose to do so at 16 or 24-bit resolution. Most studios work in 24-bit, and then when the music is released to the world, it is reduced to 16-bit (which is CD quality). Apple is saying it would be good to release 24-bit to the world - which being on an Apple platform, would probably be 24-bit AIFF files.
(You may also hear "sampling frequency" mentioned - it's out of the scope of this article to explain these, but 44.1kHz is standard, 96kHz the next-most mentioned. CDs are 16-bit, 44.1kHz, for example).
Who knows if it would catch on? It's a long way in the future, that's for sure, but with cheaper hard drives and faster networks, why not? For now though, 320kbps MP3 is going to remain the dominant format for day-to-day high quality DJ performance use, with WAVE files preferred by producers/Ableton DJs - and I can't see that changing any time soon.
What format or formats do you prefer? What experiences do you have with using less common formats with DJ software? Can you hear the difference between good MP3s and WAVEs? Let us know in the comments.