dmGSMDecode(3dm)

NAME
     dmGSMDecode - implements the European GSM 06.10 provisional standard for
     full-rate speech transcoding, prI-ETS 300 036, which uses RPE/LTP
     (regular pulse excitation/long term prediction) coding at 13 kbit/s.


SYNOPSIS
     #include <dmedia/dm_audioutil.h>

     DMstatus dmGSMDecode(DMGSMdecoder handle,
                          unsigned char *ibuf, short *obuf, int numSamples)


PARAMETER
     handle    DMGSMdecoder structure, created by dmGSMDecoderCreate(3dm),
               specifies the signal processing parameters.


     ibuf      pointer to input compressed data buffer, an array of a multiple
               of 33 bytes. The data format is unsigned char (8-bit).


     obuf      pointer to output sample data buffer, an array of size of a
               multiple of 160.  The data format is short (16-bit).  The
               samples are assumed to be two's complement.  The sampling rate
               must be 8 kHz.


     numSamples
               number of sample in the output buffer to be generated.  the
               value of numSamples passed to the GSM decode/decode routines
               must always be a multiple of 160.  The compressed bitstrem
               buffer consists of a multiple of 33 bytes.


RETURNED VALUE
     Returns DM_FAILURE or DM_SUCCESS.


DESCRIPTION
     dmGSMDecode(3dm) implements the GSM 06.10 decompression.



NOTE
     The compressed bitrate now is 13200 bits/s.  This is not the same as
     standard specification of 13000 bits/s because the first 4 bits of each
     33 byte are not useful information bits.  This bits arrangement was
     adopted using the original scheme by Jutta Degener (jutta@cs.tu-
     berlin.de) and Carsten Bormann (cabo@cs.tu-berlin.de), Communications and
     Operating Systems Research Group, TU Berlin for compatibility with
     typical UNIX applications.  And may be modify later.
     GSM algorithm was developed for sampling rate of 8 kHz.


SEE ALSO
     dmGSMDecoderCreate(3dm), dmGSMDecoderDestroy(3dm), dmGSMEncode(3dm), ETSI
     GSM 06.10 standard.