Audio Encoding 101

 

The way that digital files are encoded plays a big part in the quality of the audio, and the ability to get the crisp details of the track across, to get peoples heads bumping. In order to get the best sound from your set, we've put together a guide on the basics, and tips on how to tweak the process.

 

WHAT IS ENCODING?

Encoding is the process of changing digital audio from one format to another. There are two broad types of formats - uncompressed and compressed.

  • Uncompressed audio is mainly found in the PCM format of audio CDs. Generally, audio encoding means going from uncompressed PCM, to some kind of compressed audio format. These files take up a lot more digital space.
  • Compressed audio is split into two groups, lossless and lossy.
    • Lossless audio can be decoded back into the exact uncompressed audio you started with. This is useful for archiving audio at the highest quality possible, and for people for whom storage space is not an issue.
    • Lossy compression involves some loss of information hence the term "lossy". Computer algorithms look at the source audio, and remove up to 90% of the information.

Some common audio formats:

Uncompressed            Compressed - Lossless     Compressed - Lossy
Audio CD Apple Lossless Audio Mp3
Audio DVD TTA AAC
PCM WAV and AIFF FLAC WMA
Vinyl Record Monkey's Audio Mini Disc
Cassette Shorten
DAT WavPack

 

RE-ENCODING

When Encoding, it's best to use an Uncompressed or Lossless file, rather than another Lossy format.

Re-encoding from one Lossy format to another is called transcoding, and is generally a bad idea. Any artifacts from the initial lossy encoding will still be present, along with new (possibly far worse) ones. Also, you're unable to gain any quality by re-encoding to the same format with higher settings.

For example:

Audio CD ➞ AAC ➞ MP3 - This second step is Transcoding. The quality of encoding will be greatly reduced in the final result. The preferred alternative would be to go back to the original CD.

Audio CD ➞ MP3

 

FILE FORMATS AND CODECS

UNCOMPRESSED

WAV and AIFF

WAV and AIFF are the standard file formats for uncompressed PCM audio. Generally they will be the source material for your lossy encoded files, unless you skip the step of making uncompressed files and go straight from CD to lossy compressed encodings. 

COMPRESSED

MP3

MP3 is the compressed format most common. It uses lossy compression to greatly reduce the amount of data needed to store the audio. For DJing applications, care should be taken not to reduce the amount of data too far, to maintain the audio quality of your files.

AAC

AAC is a more recent technology, intended as the successor to MP3. It is the default encoder in Apple iTunes and is part of the MPEG-4 specification.

ALAC (Apple Lossless)

ALAC files store lossless audio data within an .mp4 container using the .m4a filename extension.

 

ENCODING TOOLS

WHAT IS AN ENCODING TOOL?

Encoding tools are programs which create audio files in a particular format, generally with options for adjusting various aspects of the file encoding process. 

Here are a couple of basic options for getting started with making your own files;

  • iTunes - comes pre-installed on all Mac computers, and is available free from Apple for Windows. iTunes can encode files of various formats and settings For more information on iTunes, check out the introduction to iTunes article.
  • LAME Frontends- LAME is a free MP3 encoder which is generally considered to give the highest quality results for Variable Bit Rate encodings at a given bit-rate.
  • RazorLame is a LAME frontend for Windows, however it doesn't rip CDs.
  • Max is a Mac LAME frontend which includes CD ripping functionality.

WHAT ARE THE BEST SETTINGS?

Bitrate

The bitrate determines the size of a file. A file's bitrate is how many bits per second are used to represent the audio. So, a 128 kbps file uses 128,000 bits per second to encode an audio signal.

  • Variable Bitrate - (VBR) is a way of saving disk space. The bitrate setting that you set becomes the maximum nitrate that can be used, and when the encoding algorithm decides it can get away with using less bits to accurately represent a part of the audio, it does so. This is why they are called Variable BitRate files.
  • Constant Bitrate - (CBR) The meaning of this file types name is obvious. The same number of bits are used to encode every second of audio.

Wikipedia article on bitrate

Joint Stereo

Joint stereo is a technique where instead of encoding the left and right channels separately, the sum and difference of both are encoded instead. Since both sides will tend to be very similar, the difference will not require a lot of data, and thus the size of the file is smaller than 'normal' stereo. This means more of the bits can be used for the 'important' information, and the quality will tend to be improved.


SOME RECOMMENDED STARTING POINTS

If you want the best quality audio from a Lossy format, the standard is 320 kbps CBR Joint Stereo. If you find that you don't have enough room to store all your music at that quality, a good compromise would be 224 kbps VBR joint stereo, although it is worth 'future proofing' your music collection by keeping the file quality as high as possible, so VBR is recommended only as a last resort. It's a good idea to keep the backup of your library in as high a format as possible. (A wise person once told me that data does not exist unless it is in more than one place.)

Beyond those starting points, it's up to you to listen to your encodings, and see what you like or not!