Creating Your Own Sound Fields - Yamaha DSP-A2 Mode D'emploi

ADVANCED FEATURES

Creating your own sound fields

What is a sound field?
In order to explain the impressive functions of the DSP, we
need to first understand what a sound field really is.
What really creates the rich, full tones of a live instrument are
the multiple reflections from the walls of the room. In addition
to making the sound "live", these reflections enable us to tell
where the player is situated, and the size and shape of the
room in which we are sitting. We can even tell whether it is
highly reflective with steel and glass surfaces, or more
absorbent with wood panels, carpeting and curtains.
The elements of a sound field
In any environment, in addition to the direct sound coming
straight to our ears from the player's instrument, there are two
distinct types of sound reflections that combine to make up the
sound field:
(1) Early Reflections.
Reflected sounds reach our ears extremely rapidly
(50 ms — 100 ms after the direct sound), after reflecting
from one surface only—for example, from the ceiling or a
wall. These reflections fall into specific patterns as shown
in the diagram on page 56 for any particular environment,
and provide vital information to our ears. Early reflections
actually add clarity to the direct sound.
(2) Reverberations.
These are caused by reflections from more than one
surface—walls, ceiling, the back of the room—so
numerous that they merge together to form a continuous
sonic "afterglow". They are non-directional, and lessen the
clarity of the direct sound.
Direct sound, early reflections and subsequent reverberation
taken together help us to determine the subjective size and
shape of the room, and it is this information that the DSP
reproduces in order to create sound fields.
If you could create the appropriate early reflections and
subsequent reverberations in your listening room, you would
be able to create your own listening environment. The
acoustics in your room could be changed to those of a concert
hall, a dance floor, or virtually any size room at all. This ability
to create sound fields at will is exactly what Yamaha has done
with the DSP.
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DSP programs consist of some parameters to determine
apparent room size, reverberation time, distance from you to
the performer, etc. In each program, these parameters are
preset with values precisely calculated by Yamaha to create
the sound field unique for the program. It is recommended to
use DSP programs without changing values of parameters,
however, this unit also allows you to create your own sound
fields. Starting with one of the built-in programs, you can adjust
those parameters. Even if the power cord of this unit is
disconnected from the AC outlet, your custom sound fields will
remain in the DSP's memory for about two weeks. The
following page details how to make your own sound fields.
In addition to the "TYPE" parameter which selects the
subprograms within each DSP program (for example, "Europe
Hall A", and "Europe Hall B" for the program 1, "CONCERT
HALL 1"), each program also has a set of parameters that
allow you to change the characteristics of the acoustic
environment to precisely create the effect you want. These
parameters correspond to the many natural acoustic factors
that create the sound field you experience in an actual concert
hall or other listening environment. The size of the room, for
example, affects the length of time between the "early
reflections"—that is, the first few widely spaced reflections you
hear after the direct sound. The "ROOM SIZE" parameter
provided in many of the DSP programs alters the timing
between these reflections, thus changing the shape of the
"room" you hear. In addition to room size, the shape of the
room and the characteristics of its surfaces have a significant
effect on the final sound. Surfaces that absorb sound, for
example, cause the reflections and reverberations to die out
quicker, while highly reflective surfaces allow the reflections to
carry on for a longer period of time. The DSP parameters allow
you to control these and many other factors that contribute to
your personal sound field, allowing you to essentially
"redesign" the concert halls, theaters, etc. provided to create
custom-tailored listening environments that ideally match your
mood and music.
Refer to "Descriptions of the digital sound field parameters" on
pages 56 to 58 for a description of what each parameter does,
how it effects the sound, and its control range.