ADVANCED RECORDING PRIMER

CHAPTER 3 - PART 10,  BY ROBERT DENNIS

REVERB TIME PARAMETERS

Reverb Time/Decay Time:

Reverb Time is the amount of time that it takes for the reverb to die out. Reverb time depends on how many reflective surfaces there are, how reflective the surfaces are and the size of the room. Increasing only reverb time makes it sound like harder surfaces more than sounding like a larger room.  Typical reverb time settings are from 1.5 seconds to 3.0 seconds. Shorter reverb times adds a clarity and moves the sound more up-front to the listener.  Longer reverb times adds lushness and bigness to the sound.   The reverb time parameter ("rt") is sometimes called reverb time-midrange ("rtm") and on some older units was called "decay time."

Reverb Time Contour:
In rooms and halls, the frequencies don't die out evenly. Generally the lows last longer and the extreme highs of the reverb die out quicker. In a typical concert hall, the very long wavelengths (low frequencies) are not well absorbed by the bodies or the air; the high frequencies, however, are attenuated by the air and absorbed by the bodies in the room. As a result the low frequencies may last 1 1/2 time as long as the mid-range frequencies and the high frequencies may die out 2 to 4 times as fast as the mid-range frequency energy.
The Reverb Time ("RT") parameter sets the mid-range reverb time. The low frequency reverb time parameter is usually called Bass Multiply. The high frequency RT (RT HF) is often expressed as a percentage ranging from 100% to 25% but is called RT High Freq Cut on some Lexicon Units. Lexicon also allows the user to change the Crossover frequency where the reverb time changes from the low-frequency setting to the mid-range setting; a usual setting would be 500 Hz but Lexicon suggests increasing it to as high as 1200 Hz when reducing low-frequency reverb time to a value lower than the mid-range reverb time (see next paragraph).
A good-quality large concert hall would have a bass multiply of 1.25 and a high frequency reverb time of .5 to .25, depending on how full the room was.  Many smaller and low-quality "conference" halls have thinner (and some times moveable) walls that don't reflect bass waves as well; to simulate this, set the bass multiply to between 1 and .5 use a slightly lower mid-range reverb time.
Plates have the same reverb time for all frequencies, one of the factors in making them less real. Small acoustic echo chambers can have a shorter reverb time in bass frequencies.

PROGRAM

RTM

BASS MULTIPLY

RTHF

HALL

2.0 - 2.5

1.50

0.25

ROOM

1.5 - 2.0

1.25

0.50

PLATE

1.5 - 2.0

1.0

1.00

CHAMBER

1.5 - 2.5

0.75

0.50

SMALL HALL

1.8 - 2.2

1.25

0.50

CONFERENCE ROOM

1.8 - 2.2

0.75 - 1.0

0,50

Copyright 1993, 2000, 2001, Robert Dennis, ALL RIGHTS RESERVED