The major audio codecs
Some general information on the most common audio codecs currently in use.
About Audio Codecs
I'm going to start by defining what a codec actually is before I move on to the audio codecs. The word codec is an abbreviation of the term compressor/decompressor. The function of a software codec is to compress data so that it takes up less storage space or bandwidth, then to decompress the data so it can be used normally again.
In relation to digital audio this means taking linear plus code modulation data (aka LPCM, the basic form of most uncompressed digital audio) and using an algorithm to decrease the number of bytes needed to contain the data. When the file is to be played back the codec expands the data again so it can be heard as normal audio.
There are two main characteristics that determine how useful an audio codec is:
• The quality of the decompressed audio (lossless codecs decompress to full quality).
• The compression ratio (the percentage the file size can be reduced by).
Most lossy codecs offer options which allow audio to be compressed at different bit rates; the higher the bit rate, the higher the audio quality and the larger the file size.
Different codecs use different amounts of computing power to compress and decompress audio. However, nowadays most devices can very easily handle the processing requirements of the common audio codecs.
So, just what are the major audio codecs at this point in time?
MP3 is by far the most common and well-known audio codec. It is a means of lossy audio data compression, where audio beyond the range of human hearing is discarded. Even though the format was first introduced in 1993 and significantly better codecs have been developed, MP3 is still the most popular codec for consumer music.
AAC was designed to be the successor to MP3. The codec generally delivers better results in terms of audio quality than MP3s encoded at similar bit rates. While AAC is a popular codec, it has never managed to achieve the universal adoption among audio devices that MP3 has. The biggest boost to the AAC format was its adoption as the default audio codec for iPods.
The SILK codec was developed by Skype for use in VoIP (Voice over Internet Protocol) calling. It was created not as a means of storing audio, but as a means of transmitting it over the internet. The SILK codec was designed with the ability to dynamically adjust the bit rate of the compressed audio so that it could automatically optimise the quality of the audio depending on how much bandwidth was available.
FLAC is a free open source audio codec which can reduce LPCM data by around 50-60% with no loss in the audio quality. While it is very high quality, the larger file sizes have limited the level of adoption.
Apple lossless is another audio codec in which there is no loss of audio quality. It also performs very similarly to FLAC in terms of the compression ratio with around a 40-60% reduction. Due to the popularity of Apple devices, the Apple lossless codec has had fairly high levels of uptake.