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Databases may be accessed directly but this is usually too inefficient for any purpose except debugging. It is expected that group files will be built which contain a binary representation of the database. A group file is a compact efficient representation of the diphone database. Group files are byte order independent, so may be shared between machines of different byte orders and word sizes. Certain information in a group file may be changed at load time so a database name, access strategy etc. may be changed from what was set originally in the group file.
A group file contains the basic parameters, the diphone index, the signal (original waveform or LPC residual), LPC coefficients, and the pitch marks. It is all you need for a run-time synthesizer. Various compression mechanisms are supported to allow smaller databases if desired. A full English LPC plus residual database at 8k ulaw is about 3 megabytes, while a full 16 bit version at 16k is about 8 megabytes.
Group files are created with the Diphone.group command which
takes a database name and an output filename as an argument. Making
group files can take some time especially if they are large. The
group_type parameter specifies raw or ulaw
for encoding signal files. This can significantly reduce the size
of databases.
Group files may be partially loaded (see access strategies) at run time for quicker start up and to minimise run-time memory requirements.