mulaw.3

speech signal process tools

.\" Copyright (c) 1989-1990 Entropic Speech, Inc.
.\" Copyright (c) 1997 Entropic Research Laboratory, Inc. All rights reserved.
.\" @(#)mulaw.3	1.6 18 Apr 1997 ESI/ERL
.ds ]W (c) 1997 Entropic Research Laboratory, Inc.
.TH MULAW 3\-ESPSsp 18 Apr 1997
.SH "NAME"
.nf
linear_to_mu - converts 14-bit integer data to 8-bit \fImu\fP-law compressed data
mu_to_linear - converts 8-bit \fImu\fP-law compressed data to 14-bit data
.fi
.SH "SYNOPSIS"
int
.br
.B "linear_to_mu(inbuf, outbuf, bufsize)"
.br
.B " short *inbuf;"
.br
.B " char  *outbuf;"
.br
.B " long   bufsize;"
.br
.sp
int
.br
.B "mu_to_linear(inbuf, outbuf, bufsize)"
.br
.B " char   *inbuf;"
.br
.B " short  *outbuf;
.br
.B " long    bufsize;"
.br
.sp
.SH "DESCRIPTION"
.PP
These two functions do quasi-logarithmic companding (compression and
expansion) of 2-byte integer data by using the \fImu\fP-law with a value
of \fImu\fP = 255. This is the North American PCM standard [1].
This compression law is linear for small amplitudes
and logarithmic for large amplitudes.
\fIInbuf\fP contains input data to be converted;
\fIoutbuf\fP contains the converted data; and
\fIbufsize\fP is the number of elements in
the \fIinbuf\fP array.
.PP
\fILinear_to_mu\fR converts
integer data with 14 significant bits (including sign) to 8 bits by using
a 15-segment, piecewise linear approximation to the \fImu\fP-law  
compression characteristic [1]. 
The conversion is done by using a binary search through an ordered 
list of input signal magnitudes.
No checking of input data magnitudes is done by \fIlinear_to_mu\fP,
so the calling routine should insure that all input samples have
magnitude <= 8159.
.PP
\fIMu_to_linear\fR converts 
8-bit, logarithmically compressed data to 14-bit linear 
data by using
the piecewise-linear \fImu\fP-law approximation.
A table lookup procedure is used to decode the magnitudes of the compressed
values.
.SH "SEE ALSO"
.PP
.SH "BUGS"
.PP
None Known.
.SH REFERENCES
[1] John C. Bellamy, "Digital Telephony", Appendix B
.SH "AUTHOR"
.PP
Manual page and program by David Burton.