Lexicon 960L owner manual Msec

Using The Reverb Program Lexicon, Inc.

Reverberation and Reality, Continued

length that is perceived, and the behavior of the reflections can be quite different when the sound event is short compared to when the sound event is long. Notes which are shorter than the time constant of the reverberation, ~RT/7, will excite the reverberation less strongly than longer notes.

There is another peculiarity of background envelopment. It depends on the absolute level of the reverberation, and not the direct/reverberant ratio. If we play the music louder the reverberation will be louder, and the sound will be more enveloping. Thus when we mix for envelopment we must be very careful about our monitor levels, and aware of how loud the critical customer will play our mix.

The perception of background envelopment depends on the same fluctuations in interaural time delay that cause the sense of distance. But the background is only detected when the direct sound has ceased, and only reflections are hitting the ears. Thus if the reflections come from all around us the fluctuations, and the sense of envelopment will be maximum. If reflections come only from the front we will not get much envelopment at all.

The perception of envelopment requires that the interaural time delay and level differences should be fluctuating. In a small relatively dead room the only way these differences can fluctuate is if you have at least two sound sources, and the relative phase between these sources is fluctuating. (Ideally these sound sources should be reproducing decorrelated reverberation.) The optimum direction for these two sound sources (loudspeakers) depends on frequency. Once again below 700Hz the optimum direction is from the side, and as the frequency goes up the optimum angle moves toward the medial plane – closer to the front, or closer to the rear.

Although envelopment can be perceived at all frequencies, psychologically the low frequencies are particularly important. For example, even in a dead room a standard two channel loudspeaker system (+/-30 degrees from the front) can produce envelopment if the sound source is decorrelated and contains primarily frequencies above 1000Hz – such as strings or applause. But low frequency envelopment, the life blood of lower strings and basses, is missing. Add low frequency uncorrelated reverberation to loudspeakers at the sides, and the life magically returns. (For a more thorough overview of this subject, see David Griesinger's web page at www.lexicon.com/links.)

Initial Phone

Perceived

as Part of

Phone

Risk of Reduced

Intellgibility

Reverberance

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