Audio formats

Almost all audio files contain both the audio and the tags.
Tags are small pieces of information like album title, track number, track title, artist, cover art, etc. Most of the time the tags are in the header.
Tags makes the file self-documenting.
If you move an audio file to e.g. a portable, the media player reads the tags and displays them in the interface.

More about tagging.

Types

Audio files come in three flavors.

• lossless uncompressed
• lossless compression
• lossy compression

Lossless and uncompressed

Well-known examples are WAV (Waveform audio format, developed by Microsoft and IBM) and AIFF (Audio Interchange File Format, a format developed by Apple Computer in 1988).
Most of the time they contain audio in uncompressed PCM (Pulse Code Modulation) format.
If you rip a CD straight to WAV, you rip 16 bit/44.1 kHz PCM Red book audio format to 16 bit/44.1 kHz PCM in WAV format, this is as close as you can get to the original source.

 

Pro:
No loss of quality
If you have your audio in a lossless format you can convert to any other lossless format without generation loss.

 

Cons:
Uses a lot of disk space.
In case of Redbook audio: bits * sample rate * channels = 16 * 41000 * 2=1411200 Bits/sec ≈ 172 Kb per second.

Today a 1 Tb HD sells at € 50,-
You can store approximately 1600 CD’s on it.

 

Tagging WAV is a problem. Due to a lack of standardization portability of the tags is poor.
Best practice is probably to act as if tags in WAV are not supported at all.

Lossless compression

The data is compressed without any loss of information. This is similar to how WinZip works, except you get a better compression because the software is designed specifically for audio. Examples are: FLAC  (Free lossless Audio Codec), Monkey's Audio (APE), WavPack (WV), Tom's lossless Audio Kompressor (TAK), Apple Lossless (ALAC) and Windows Media Audio Lossless (WMAL).

Over the years FLAC has gained momentum.
It is probably the most popular non-proprietary format in this category.

 

Pro:

• No loss of quality.
• Reduces file size 40 to 60% depending on the kind of music.
• Tagging support

Cons:

• Limited support. Apple and Microsoft support their own proprietary lossless formats only.
• Not as frugal on disk space as MP3.

Lossy compression

MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding, lossy compression format, an algorithm designed to greatly reduce the amount of data required to represent audio.

It was invented by a team of European engineers of Philips, CCETT (Centre commun d'études de télévision et télécommunications), IRT and Fraunhofer Society, who worked in the framework of the EUREKA 147 DAB digital radio research program, and it became an ISO/IEC standard in 1991.

 

Several bit rates are specified in the MPEG-1 Layer 3 standard: 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 192, 224, 256 and 320 Kbit/s, and the available sampling frequencies are 32, 44.1 and 48 kHz.

Higher rates then 320 don't make sense; the file size will equal those of lossless compression.

 

Pro:

• high compression so frugal on disk space.
• Strong support, few players has the nerve not to support this format.
• Tagging standard (ID3)

Cons:

• the stronger the compression the higher the loss of quality.
• you can't convert back to a lossless format.
• Generation loss. If you convert to an other lossy format you accumalete the artefacts of MP3 plus the artefacts of the other lossy format.