ABOUT SPEECH FILE COMPRESSION AND UNCOMPRESSION
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All speech data files in this release of the TIDIGITS corpus (*.wav)
are stored on the CD-ROMs in compressed form.  The particular form of
compression used is version 2.0 of ``shorten'', developed by Tony
Robinson at Cambridge University.  This algorithm is intended to give
optimal compression results for speech sample data.

Two software implementations of shorten are available.  Both will
provide the same output when uncompressing the TIDIGITS speech data,
and complete source code packages are included here for both.

One is a stand-alone program developed by Tony Robinson (in the
``shorten'' directory).  This package includes a pre-compiled
executable program file for MS-DOS users (shorten.exe), so that MS-DOS
users do not need a C compiler system to get started.  (Users of other
operating systems will need a C compiler and related utilities to make
an executable program from the source files; but assuming these are
available, the actual compilation is very simple.)

The other is as embedded functions within the NIST SPHERE software
package (in the ``sphere'' directory).  This package must be installed
via a process involving creation of some object library files and
several executable utility programs; this installation process is
designed for use with the UNIX operating system, and is unlikely to be
easily adaptable to other systems.

In terms of choosing which implementation to use, people who are not
using UNIX platforms should simply use the stand-alone shorten
program; this will be sufficient to provide uncompressed sample data.

People who are using a UNIX system will have a choice of using shorten
or sphere.  These differ in the following regards.  Stand-alone
shorten is compact, and is easy and quick to install and use, but it
does only one thing: compression or uncompression of speech files.
The sphere package is much larger, takes longer to install, and may
require custom installation steps on some UNIX systems; execution
speed may be slightly slower (but perhaps not significantly so);
program usage is only slightly more complicated, by virtue of having
options to support a wider range of activities.  The ``w_decode''
utility can produce uncompressed output with selectable byte order.
It also makes sure that the file header of the resulting file is
updated to reflect all changes to the file contents; this allows for
use of other sphere utilities (w_edit, h_edit, h_read, etc) on the
output data, which can be very convenient.

UNIX users should NOT use both packages (e.g. shorten to uncompress
and other sphere utilities to do other things); shorten will not
modify the file headers, and this will cause the sphere utilities to
perform incorrectly on the resulting files.  If you intend to use
other sphere utilities (or other processes that recognize and use
sphere file headers), be sure to use ``w_decode'' for uncompression.

The following explains how to use each package to uncompress the
waveform data; it will be assumed that the programs can be found in
the user's current execution path, and that the names ``infile.sph''
and ``outfile.sph'' represent suitable file names, with directory
paths included if necessary, to locate and identify the input and
output files.

SHORTEN:

	shorten -x -a 1024 infile.wav outfile.wav

(The "-a 1024" option specifies that the 1024-byte sphere header
should be passed through unmodified to the output file; without this
option, the command will fail.)

SPHERE:

	w_decode -o pcm infile.wav outfile.wav

(The "pcm" argument can be replaced with "pcm_10" or "pcm_01", to
force the output samples to be high-byte-first or low-byte-first,
respectively; the command as shown above will produce output samples
with the native byte order of the system on which the sphere package
was installed.)

In both cases shown above, it is possible to replace "outfile.wav"
with a dash "-", representing stdout, in order to have the
uncompressed data piped directly to some other process (e.g. a d/a
playback program).

Note that the compression has been done in a way that leaves the
sphere headers uncompressed; it is therefore possible to read the
headers without having to uncompress the files first.