Toshiba CF35E50, Technical Training Manual

Page: 113 / 139

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As shown in Fig.1 5-4, a sound emitted in a sound field can
be classified as a direct sound which directly reaches ears of
a listener, and reflected sound which comes after collision
with a wall as shown by dotted line or comes after several
times of collision as shown by double dotted lines. The
listeners are determining that they are listing in what type of
location by perceiving time difference and volume level
difference between the direct sound and the reflected sound.
For more detail, this situation can be expressed with the
direct sound, initial reflection sound coming after one time
of reflection, and trains of reverberation sound in later period
as shown in Fig. 15-5.
The DSP circuit develops these initial reflection sound and
the reverberation sound artificially and add them to the
original sounds, thereby creating rhe effect that allows the
listeners in the home listening room to feel as if they are
listening in an original location.
The DSP IC YM7128B has eight separate output taps and
their delay time and the output levels can be specified
separately, so, various sound fields can be selected by
varying the initial reflection sound. Moreover, the IC has an
internal feedback loop which controls the delay time and the
output level in considering the later time reverberation
sound.
Fig. 5-4 Fig. 5-5
Direct Sound
Initial Reflection
Sound
Reverberation
Sound
Sound Level
Direct Sound
Initial Reflection Sound
Reverberation Sound
Time