AFsetInputPar

Routine:

int AFsetInputPar(const char String[])

Purpose:

Set defaults for input audio files from a string specification

Description:

This routine sets the default audio file data parameters. These parameters are used when opening input audio files with unrecognized (non-standard) headers or files with no headers (raw audio files). Note that the parameters do not override values specified in the file headers of standard input files.

This routine must be called before opening the file with AFopnRead. The parameters for AFsetInputPar are determined from an input string which consists of a list of parameters separated by commas. The form of the list is

  "Format, Start, Sfreq, Swapb, Nchan, FullScale"

Format: File data format

 "undefined" - Headerless files will be rejected
 "A-law8"    - 8-bit A-law data
 "mu-law8"   - 8-bit mu-law data
 "mu-lawR8"  - 8-bit bit-reversed mu-law data
 "unsigned8" - offset-binary 8-bit integer data
 "integer8"  - two's-complement 8-bit integer data
 "integer16" - two's-complement 16-bit integer data
 "integer24" - two's-complement 24-bit integer data
 "integer32" - two's-complement 32-bit integer data
 "float32"   - 32-bit floating-point data
 "float64"   - 64-bit floating-point data
 "text16"    - text data scaled as 16-bit integers
 "text"      - text data

Start: byte offset to the start of data (integer value)

Sfreq: sampling frequency in Hz (floating-point value)

Swapb: data byte swap parameter

 "native" - no byte swapping
 "little-endian" - file data is in little-endian byte order and will be
   swapped if the current host uses big-endian byte order
 "big-endian" - data is in big-endian byte order and will be swapped if
   the current host uses little-endian byte order
 "swap" - swap the data bytes

Nchan: number of channels

The data consists of interleaved samples from Nchan channels

FullScale: full scale value for the data in the file.

This value is used to scale data from the file to fall in the range -1 to +1. If the FullScale value is set to "default", the FullScale value is determined based on the type of data in the file as shown below.

   data type            FullScale
 8-bit A-law:               32768
 8-bit mu-law:              32768
 8-bit bit-reversed mu-law: 32768
 8-bit integer:             256
 16-bit integer:            32768
 24-bit integer:            256*32768
 32-bit integer:            65536*32768
 float data:                1
 text16 data:               32768
 text data:                 1

The value of FullScale can be specified as a value or ratio of values.

The default values for the audio file parameters correspond to the following string.

  "undefined, 0, 8000., native, 1, default"

Leading and trailing white-space is removed from each item. Any of the parameters may be omitted, in which case whatever value has been previously set remains in effect for that parameter. The string ",512, 10000." would set the Start and Sfreq parameters and leave the other parameters unchanged.

If the input string contains has a leading '$', the string is assumed to specify the name of an environment variable after the '$'. This routine uses the value of this environment variable to determine the parameters. If this routine is called as AFsetInputPar("$AF_SETINPUTPAR"), this routine would look for the parameter string in environment variable AF_SETINPUTPAR.

Parameters:

<- int AFsetInputPar: Error flag, zero for no error
-> const char String[]: String containing the list of parameters for headerless files or the name of an environment variable (with a leading $)

Author / revision: