dmFS1016Encode(3dm)					   dmFS1016Encode(3dm)

NAME    [Toc]    [Back]

     dmFS1016Encode - implements the US	Federal	Standard 1016 4800/7200/9600
     bits/s CELP (Code Excited Linear Predictive) Voice	Coder.

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/dmedia.h>
     #include <dmedia/dm_params.h>
     #include <dmedia/dm_audioutil.h>

     DMstatus dmFS1016Encode(DMFS1016encoder handle,
		       short *ibuf, unsigned char *obuf, int nsamples)

PARAMETER    [Toc]    [Back]

     handle    DMFS1016encoder structure, created by
	       dmFS1016EncoderCreate(3dm), specifies the signal	processing
	       parameters.


     ibuf      pointer to input	sample data buffer. The	data format is short
	       (16-bit).  The samples are assumed to be	two's complement.  The
	       sampling	rate must be 8 kHz.


     obuf      pointer to output data buffer.  The data	format is unsigned
	       char (8-bit).  This bitstream buffer must consist of a multiple
	       of 18 bytes.


     nsamples  number of samples in the	input buffer to	be processed.  The
	       value of	nsamples passed	to FS1016 decode/decode	routines must
	       always be a multiple of 240, 160, or 120	for operations of
	       4800, 7200, or 9600 bits/s respectively.

RETURNED VALUE    [Toc]    [Back]

     Returns DM_FAILURE	or DM_SUCCESS.

DESCRIPTION    [Toc]    [Back]

     dmFS1016Encode(3dm) implements the	Federal	Standard 1016 decompression.
     The uncompressed data sampling rate is 8000 Hz.  The compression bitrate
     can be

     DM_FS1016_4800_BITS    [Toc]    [Back]
     DM_FS1016_7200_BITS
     DM_FS1016_9600_BITS






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dmFS1016Encode(3dm)					   dmFS1016Encode(3dm)



     and is set	by a call to dmFS1016EncoderSetParams(3dm). Without calling
     dmFS1016EncoderSetParams(3dm), encoder sets default to 4800 bits/s.


     dmFS1016Encode(3dm) algorithm uses	linear prediction analysis operations
     that simply delays	the output by half of the analysis frame size.
     Therefore the delays are 120, 80, or 60 samples for operations of 4800,
     7200, or 9600 bit/s respectively.	In file	conversion expecting N samples
     in	and out, the output signal is offset by	120, 80, or 60 samples from
     the first sample.	The application	may want to discard the	first 120, 80,
     or	60 samples returned in output date buffer from dmFS1016Decode.


     FS1016 compression	uses a linear prediction scheme.  This means that the
     compressed	bits, which carrying compressed	information, are interrelated
     or	interdependent.	 If a application calls	afSeekFrame() to an offset
     into the compressed bit stream file and then starts reading bits in the
     middle of the bit stream and decompress them with dmFS1016Decode(3dm),
     the interdependency of the	bits at	the cutting point is lost.  The
     application will initially	get back data with a lower amplitude than if
     he	had read the same data back during a complete pass over	the file from
     the beginning.


     There is no way to	exactly	recreate the decoded data in the middle	of the
     bit stream	file without going all the way back to the beginning.
     However, with a "preroll" value to	read ahead a portion of	the compressed
     file, application can compensate for the amplitude	problem.  We recommend
     2 second "preroll".

NOTE    [Toc]    [Back]

     FS1016 algorithm was developed for	sampling rate of 8 kHz.

SEE ALSO    [Toc]    [Back]

     dmFS1016EncoderCreate(3dm), dmFS1016EncoderDestroy(3dm),
     dmFS1016Decode(3dm), dmFS1016EncoderSetParams(3dm), Federal Standard
     1016.


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