Global Music Resource

RIFF (Resource Interchange File Format) was developed by Microsoft and is a file that will hold digital audio. The file is divided into “chunks” (data blocks) and sub-chunks. The WAV (Waveform Audio) audio file format is a subset of RIFF, and is the most widely used digital format used today due to its development by Microsoft and IBM for the Windows 3.1 and higher operating system. This file format is usually an uncompressed, PCM, raw bit stream data file, which also includes additional information in a format chunk (header) and footer block that describes the sample to the device that will be used process the data. The digitized audio is in separate a Data Chunk. The sampling rate is at 44.1KHz, the resolution is at 16-bits, and in stereo but can also be sampled at lower rates, resolution and in mono. Secondly, this uncompressed, PCM format has good sound quality but takes up more memory space than other formats (encoded at 1,411kbps).

The PCM Data Chunk can be compressed while the Header will still identify the file as a WAV. The WAV format will support various bit resolution, u-law, a-law, IMA ADPCM, MS ADPCM, and MPEG. Most software applications will continue to read and display the file as a WAV. The PCM .wav can be adjusted by an algorithm utilized by various hard disk recording / editing software applications for pitch shift but it is still essentially a WAV file. The format is versatile enough that one can even rename a .wav file on MS Windows and save it as an .aif file which will be compatible with a Mac OS computer.

There is a subset of WAV, specified by the European Broadcasting Union, known as BWF (Broadcast Wave Format). The BWF is restricted to linear PCM encoding, 16-bits and 48 KHz and requires an additional Information Chunk. The file may also be sampled at 44.1 KHz but may not be transmitted to another party without prior consent. Note that the audio dated within a BWF may also be MPEG encoded. The BWF is primarily utilized in television and radio production and transmission. The average system should be able to play the digital audio data but may not be able to read and display the information in the extra Data Chunk. There is no actual .bwf file extension. Rather, the .wav or .mpg file extension is used.

Another common format is the AIFF (Audio Interface/Interchange File Format), which is a proprietary format developed by Apple Computers, Inc., for the Macintosh computer operating system. This format is also PCM uncompressed, supports sampling at various rates up to 44.1 KHz, up to 32-bit resolution and in stereo with very good sound quality. The file consists of a common “chunk” that holds information about sampling rate. A data chunk contains the actual audio data. One will sometimes see a AIFF-C or AIFC File. This is a compressed AIFF File. The compression is done by the proprietary MACE 3 (3 to 1) and MACE 6 algorithms. Both formats will also support the Quicktime codec.

Both of these formats contain space for extra digitized information (header and footer bit blocks) that indicates the number of channels, number of sample frames, sample size and rate, block alignment, synchronization points, and text (not just in English only) that identifies the author, name and copyright details.

On Sun MicroSystem NeXT hardware this digital audio format is known as SND. SND can also contain FM and Wave table synthesis data. The SND format also appeared on early Apple computers. The Type 2 SND is the format for actual digitized data. Sun Audio (AU), utilized by Sun Microsystems unix operating system hardware is similar to a SND file. The AU file is also supported by Java programs. Both AU and SND files will support various sample rates, U-Law and A-Law and linear and logarithmic encoding, 32-bit resolution, 64-bit floating rate resolution, and ADPCM.