Artificial Reverberation

Why use it?

There are three basic reasons: (1) to simulate a particular acoustic environment e.g. in a drama scene set in a church a relatively long reverberation time must be added to the recordings made in a studio; (2) in music, to enhance or ‘sweeten’ the sound, e.g. to simulate the acoustics of a concert hall; (3) for special musical or dramatic effects where there is no attempt at realism.

Artificial reverberation devices

In the past there have been several devices designed to simulate artificial reverberation. These have included ‘echo’ rooms, reverberation plates and special springs. Within the last decade digital reverberation units have become available at costs ranging from the equivalent of a pair of medium-priced microphones to ten or more times as much. However, even the low-priced models are capable of a very realistic simulation of reverberation.

Features of digital units

● The reverberation time can be varied from, typically, less than 1 second to 10 or more seconds. On the less expensive devices there may be a limited range of perhaps four settings.

● ‘Predelay’. Aural assessment of an environment includes not only the reverberation time but also the time gap between the direct sound and the first reflections, often referred to as ‘predelay’. This is variable on most digital reverberation units. In the simpler ones it may appear as a range of ‘room sizes’.

● Early (and other) reflections. The acoustic quality of a room is affected by the more-or-less discrete reflections in the early stages of the reverberation. These can be simulated in many digital units and may be incorporated into programs which can be called up with specific names. Included among them is often a ‘plate’ program, for those who, as mentioned above, prefer the quality of plate reverberation.

● Filters. These alter the reverberation time/frequency characteristic.

● Storage of programs. The more expensive units contain memories so that particular settings of reverberation time, program, predelay and filters can be stored for rapid recall. This is particularly useful when the character of the artificial reverberation needs to be changed quickly. These memories are usually non-volatile so that switching off the unit does not wipe the contents of the memory.

‘t’ is the time for the first reflected sound to reach the listener after the arrival of the direct sound. If it is more than about 40 ms then the listener is aware of a time gap. If less than 30–40 ms the time interval is not conciously perceived but is nevertheless used by the listener to assess the apparent size of the room. Thus for correct simulation, say for drama purposes, of a particular-sized environment the choice of an appropriate ‘pre-delay’ is important.

Digital reverberation unit

A typical unit with adjustable predelay and a choice of several reverberation simulations.