User Guide

Other examples include the ability to play 16-bit sounds on an 8-bit-only
sound card, or playing stereo sounds on a mono-only sound card.You can also
record stereo files on a mono-only sound card. However, this last example is
essentially useless because the Sound Mapper will duplicate the mono input of
your sound card in both channels. So keep in mind that the Sound Mapper cannot
create something that is better than what the sound card can supply.
The usefulness of the Sound Mapper for non-compressed sound files can be
summarized as convenience. You don’t have to convert the sound to a
supported format before you listen to it. Some of the tasks that the Sound Mapper
can perform (like format conversions while recording) are available not
because they are useful in real world situations, but because the developers of
the ACM knew it could be done. Much like climbing a mountain for no better
reason than it’s there.
So what about compressed sound files? The Sound Mapper allows you to play (and
sometimes record) compressed sound files. Even on sound cards that do not
support compression directly. So you can play a sound file that is compressed
with Microsoft ADPCM or The DSP Group’s TrueSpeech on any sound card
without decompressing the sound file first. Many multimedia and
entertainment software titles use compressed sound files to save disk space.The
software then plays the files through the Sound Mapper.
Above we mentioned that Sound Mapper can sometimes record compressed
sound files.The reason for this (even when the compressed file can be played)
is simple. Compressing sound data can be very computationally expensive (it
takes a long time); the amount of time required is completely dependent on
the compression algorithm and how it is implemented. Decompressing sound
data is almost always faster than compressing the same sound data, which
makes it possible to play it back in real time.
It should be noted that Sound Forge XP does not play and record compressed
sound files directly. Rather, all compression and decompression is performed
while opening and saving the sound files. This limitation is actually
insignificant; Sound Forge XP is the perfect tool for authoring compressed
sound files for the ACM and many software authors are using Sound Forge XP
for exactly this. Sound Forge XP saves compressed sound files using the best
quality possible – something that cannot always be done in real time. So saving
compressed sound files with Sound Forge XP will usually sound better than
those recorded with audio compression.
APPENDIX E
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