3Com CP-1 owner manual Speaker Set-Ups for Pro Logic

Theory

and

Design

CP-1 Digital Audio Environment Processor

sounds appear in the front left and right speakers (and the side left and right speakers, if present).

The Rear Noise Chip parameter is preset to OFF, meaning that the high- frequency sound in the rear channels is set solely by the Rear Rolloff parameter. (The Rear Noise Chip should be ON for Dolby Surround programs.) Rear Rolloff is preset to 14.1 kHz, its highest constant value. An Automatic mode expands to accommodate signals steered to the rear, then shuts down to 7 kHz for lower percussion leakage when there are no signals there. This is a useful feature for films.

The Stereo Logic Program can provide an unusual and revealing way to listen to music. With a multi-speaker surround system the program puts you in the middle of the music, so that interior elements formerly buried in the mix become audible. Try setting Front Effect and Rear Effect all the way up; then mute the center channel by pushing System Mute to turn main and effects signals off, then Effects Mute to turn everything but the center back on. This allows you to hear all of the mix (except for strongly centered

Speaker Set-Ups for Pro Logic

material such as vocals) separated and spread throughout the room. This method also provides an interesting look into the details of film sound mixes.

The requirements for film sound are quite different from those for the playback of music. The most important track in any film is the dialog. When the two stereo channels are played back through two speakers with no decoder, dialog will appear to come more or less from the center, but only for those listeners on the center line of the main stereo pair.

The most important job for a Pro Logic decoder is canceling the dialog from left and right loudspeakers. To be able to hear this you have to set up a center speaker. We strongly recommend that a center channel speaker be used with any surround decoder; the difference it can make to the subjective quality of a film is enormous.

Assuming some form of center speaker has been provided, the next most important point is providing enough spatial impression. Once again, the best way to do this is with loudspeakers at the sides of the listeners. When we tried this with the CP-1 we made an interesting discovery. When the Left and Right loudspeakers are spread wide enough to fall within 20 degrees of the listeners' sides, there is a tremendous change in the impact of the film. The sound stage becomes much wider than the screen - so wide in fact that the listener is literally drawn into the action. This effect should not be surprising - lateral sound is known to grab our attention in a way that front

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