gsm_create,   gsm_destroy,   gsm_encode,   gsm_decode   --
       GSM 06.10 lossy sound compression


SYNOPSIS

       #include "gsm.h"

       gsm gsm_create();

       void gsm_encode(handle, src, dst)
       gsm handle;
       gsm_signal src[160];
       gsm_frame dst;

       int gsm_decode(handle, src, dst)
       gsm handle;
       gsm_frame src;
       gsm_signal dst[160];

       void gsm_destroy(handle)
       gsm handle;


DESCRIPTION

       Gsm is an implementation of  the  final  draft  GSM  06.10
       standard for full-rate speech transcoding.

       gsm_create()  initializes  a  gsm pass and returns a 'gsm'
       object which can be used as a handle in  subsequent  calls
       to gsm_decode(), gsm_encode() or gsm_destroy().

       gsm_encode() encodes an array of 160 13-bit samples (given
       as gsm_signal's, signed integral values  of  at  least  16
       bits)  into a gsm_frame of 33 bytes.  (gsm_frame is a type
       defined as an array of 33 gsm_bytes in gsm.h.)

       gsm_decode() decodes a gsm_frame  into  an  array  of  160
       13-bit  samples (given as gsm_signals), which sound rather
       like what you handed to gsm_encode() on the other side  of
       the wire.

       gsm_destroy()  finishes  a  gsm pass and frees all storage
       associated with it.

   Sample format
       The following scaling is assumed for input  to  the  algo­
       rithm:
          0  1                             11 12
          S..v..v..v..v..v..v..v..v..v..v..v..v..*..*..*
       Only the top 13 bits are used as a signed input value.
       The output of gsm_decode() has the three lower bits set to zero.


RETURN VALUE

       gsm_create()  returns an opaque handle object of type gsm,
       or 0 on error.  gsm_decode()  returns  -1  if  the  passed



EXAMPLE

       #include "gsm.h"

       gsm handle;
       gsm_frame buf;
       gsm_signal sample[160];
       int cc, soundfd;

       play() {  /* read compressed data from standard input, write to soundfd */

            if (!(handle = gsm_create())) error...
            while (cc = read(0, (char *)buf, sizeof buf)) {
                 if (cc != sizeof buf) error...
                 if (gsm_decode(handle, buf, sample) < 0) error...
                 if (write(soundfd, sample, sizeof sample) != sizeof sample)
                      error...
            }
            gsm_destroy(handle);
       }

       record() {     /* read from soundfd, write compressed to standard output */

            if (!(handle = gsm_create())) error...
            while (cc = read(soundfd, sample, sizeof sample)) {
                 if (cc != sizeof sample) error...
                 gsm_encode(handle, sample, buf);
                 if (write(1, (char *)buf, sizeof buf) != sizeof sample)
                      error...
            }
            gsm_destroy(handle);
       }


BUGS

       Please  direct  bug  reports  to jutta@cs.tu-berlin.de and
       cabo@cs.tu-berlin.de.


SEE ALSO

       toast(1), gsm_print(3), gsm_explode(3), gsm_option(3)


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