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<H4><A name=_dx_sound_cones_dxaudio></A>Sound Cones</H4>
<P>A sound with no orientation has the same amplitude at a given distance in all
directions. A sound with an orientation is loudest in the direction of
orientation. The model that describes the loudness of the oriented sound is
called a sound cone. Sound cones are made up of an inside (or inner) cone and an
outside (or outer) cone. </P>
<P>At any angle within the inner cone, the volume of the sound is just what it
would be if there were no cone, after taking into account the basic volume of
the buffer, the distance from the listener, the listener's orientation, and so
on. </P>
<P>At any angle outside the outer cone, the normal volume is attenuated by a
factor set by the application. The outside cone volume is expressed in
hundredths of decibels and is a negative value, because it represents
attenuation from the default volume of 0.</P>
<P>Between the inner and outer cones is a zone of transition from the inside
volume to the outside volume. The volume decreases as the angle increases.</P>
<P>The following illustration shows the concept of sound cones.</P>
<P><IMG alt="" border=0
src="http://www.msdn.microsoft.com/library/psdk/directx/dx8_c/hh/directx8_c/images/soundcon.gif"></P>
<P>Every 3-D sound buffer has a sound cone, but by default a buffer behaves like
an omnidirectional sound source, because the outside volume is not attenuated,
and the inside and outside cone angles are 360 degrees. Unless the application
changes these values, the sound does not have any apparent orientation.</P>
<P>Designing sound cones properly can add dramatic effects to your application.
For example, you could position a sound source in the center of a room, setting
its orientation toward an open door in a hallway. Then set the angle of the
inside cone so that it extends to the width of the doorway, make the outside
cone a bit wider, and set the outside cone volume to inaudible. A listener
moving along the hallway will begin to hear the sound only when near the
doorway, and the sound will be loudest as the listener passes in front of the
open door.</P></FONT></DIV></BODY></HTML>