Audio File Format Specifications

File Description: IRCAM soundfile / bicsf (Berkeley/IRCAM/Carl Sound Format) file
File Extension: Commonly .sf
File Byte Order: Big-endian or little-endian

Prof. Peter Kabal, MMSP Lab, ECE, McGill University: Last update: 2017-01-20

IRCAM File Specifications

The IRCAM Soundfile format originated from the Institut de Recherche et Coordination Acoustique / Musique in Paris. This format has been subsequently used in a number of programs.

Header Structure

The header structure is simple but the codes used have not always been consistent. The header size is 1024 bytes. The first part is fixed, the last part can be used for comments and other information.

Offset Length Type Contents
0 4 character Identifier
4 4 float Sampling frequency
8 4 integer Number of interleaved channels
12 4 integer Data type
16 - - Additional information

File Identifier

The identifier for VAX machines was 107364 or \144\243\001\0 in little-endian byte order. The second last byte was then appropriated to indicate the type of machine.

Note that the two MIPS machines have different byte-orders.

The present situation is that 7 codes seem to be accepted. In the following table the identifier is given in the order in which it is stored in the file.

Identifier File Byte Order Machine code
\144\243\001\0 Little-endian VAX (native)
\0\001\243\144 Big-endian VAX
\144\243\002\0 Big-endian Sun (native)
\0\002\243\144 Little-endian Sun
\144\243\003\0 Little-endian MIPS (DECstation)
\0\003\243\144 Big-endian MIPS (SGI)
\144\243\004\0 Big-endian NeXT

Sampling Frequency

The float sampling frequency can be problematic. For VAX computers, the float format is different from the IEEE format used in modern machines. However, the case where a VAX machine code was used, but the file byte order is big-endian, the file was probably written on a Sun computer which does use IEEE floats. See the description of INRS-Telecom Speech Files for a table look-up approach for standard sampling frequencies (VAX floating point format) frequencies. Alternately, a web search will find routines for converting VAX float values to IEEE float values.

A reasonable strategy for modern files is to assume that floats are in IEEE float format.

Data Types

The sample format code is one of the following.

Code PreProcessor Symbol Data
0x00001 SF_CHAR 8-bit integer
0x10001 SF_ALAW 8-bit A-law
0x20001 SF_ULAW 8-bit -law
0x00002 SF_SHORT 16-bit integer
0x00003 SF_24INT 24-bit integer
0x40004 SF_LONG 32-bit integer
0x00004 SF_FLOAT 32-bit float
0x00008 SF_DOUBLE 64-bit float

Note that the code has the data length in the least significant part. These codes are not consistently applied, for instance the MIT Media Lab Csound package defines SF_ULAW as 0x00001.

There is also an ambiguity as to the normalization that should be applied to float data. In some cases, full-scale data is normalized to a maximum absolute value of one. In other cases, the data is written with no normalization, and so will often have a maximum amplitude of 32768.

Additional Header Information

The additional header information is stored as chunks. There common types of information chunks in use are SF_COMMENT for comments, SF_MAXAMP for maximum amplitude information, and SF_END to mark the end of the informatinon chunks.

Comment chunk

Offset Length Type Content
0 2 integer Code, SF_COMMENT (2)
2 2 integer Length of comment in bytes
4 - character Comment

Maximum Amplitude Chunk

The maximum amplitude chunk has a peak value and location for each channel. It also includes a time tag which indicates when this chunk was updated.

Offset Length Type Contents
0 2 integer Code, SF_MAXAMP (1))
2 2 integer Length of information (12n)
4 4n float Peak amplitude, n values
4+4n 4n integer Location of peak amplitude sample
4+8n 4n integer Time tag (seconds since Jan. 1, 1970)

End Chunk

Offset Length Type Contents
0 2 character Code, SF_END (0)
2 2 integer Chunk length. 0

Symbols for other informational chunks (SF_PVDATA, SF_AUDIOENCOD and SF_CODMAX are defined in the source code for Sox (see SoX - Sound eXchange). These are not used, nor is there any indication of their purpose.

Sample Files

addf8-sun-be.sf (48 kB)
IRCAM file, Sun code, big-endian data, 8 kHz, 16-bit integer data
addf8-vax-be.sf (48 kB)
IRCAM file, VAX code, big-endian data, 8 kHz, 16-bit integer data
addf8-mips-be.sf (48 kB)
IRCAM file, MIPS code, big-endian data, 8 kHz, 16-bit integer data
manna-mips-le-f.sf (93 kB)
IRCAM file, MIPS code, little-endian data, 44.1 kHz, 32-bit float data (from the Audio File Library) - the data is normalized to a maximum value of 1.