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<BODY bgColor=#fffbf0>
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<DIV><FONT face=Arial size=2>
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<H4><A name=_dx_sound_cones_dxaudio></A>Sound Cones</H4>
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<P>A sound with no orientation has the same amplitude at a given distance in all
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directions. A sound with an orientation is loudest in the direction of
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orientation. The model that describes the loudness of the oriented sound is
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called a sound cone. Sound cones are made up of an inside (or inner) cone and an
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outside (or outer) cone. </P>
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<P>At any angle within the inner cone, the volume of the sound is just what it
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would be if there were no cone, after taking into account the basic volume of
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the buffer, the distance from the listener, the listener's orientation, and so
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on. </P>
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<P>At any angle outside the outer cone, the normal volume is attenuated by a
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factor set by the application. The outside cone volume is expressed in
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hundredths of decibels and is a negative value, because it represents
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attenuation from the default volume of 0.</P>
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<P>Between the inner and outer cones is a zone of transition from the inside
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volume to the outside volume. The volume decreases as the angle increases.</P>
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<P>The following illustration shows the concept of sound cones.</P>
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<P><IMG alt="" border=0
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src="http://www.msdn.microsoft.com/library/psdk/directx/dx8_c/hh/directx8_c/images/soundcon.gif"></P>
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<P>Every 3-D sound buffer has a sound cone, but by default a buffer behaves like
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an omnidirectional sound source, because the outside volume is not attenuated,
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and the inside and outside cone angles are 360 degrees. Unless the application
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changes these values, the sound does not have any apparent orientation.</P>
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<P>Designing sound cones properly can add dramatic effects to your application.
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For example, you could position a sound source in the center of a room, setting
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its orientation toward an open door in a hallway. Then set the angle of the
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inside cone so that it extends to the width of the doorway, make the outside
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cone a bit wider, and set the outside cone volume to inaudible. A listener
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moving along the hallway will begin to hear the sound only when near the
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doorway, and the sound will be loudest as the listener passes in front of the
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open door.</P></FONT></DIV></BODY></HTML>
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