Electrical audio signal processing systems and devices – Sound effects – Reverberators
Patent
1996-04-15
1998-03-17
Kuntz, Curtis
Electrical audio signal processing systems and devices
Sound effects
Reverberators
84630, H03G 300
Patent
active
057296138
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to assisted reverberation systems and PA or speech reinforcement systems that utilise reverberation devices.
BACKGROUND ART
Public address and speech reinforcement systems are used to amplify and broadcast voice signals. In these systems, microphones are placed close to the performers and the microphone signals are amplified, processed and fed to amplifiers and loudspeakers for broadcasting. In such systems, the loudspeaker signals couple back to the microphones, and if the gain is too high, the system can become unstable. This feedback between the loudspeakers and microphones is minimised by using directional microphones and having the microphones close to the performers to maximise the signal level.
An assisted reverberation system is used to improve and control the acoustics of a concert hall (auditorium). There are two fundamental types. The first is the in-line system, in which the direct sound produced on stage by the performer(s) is picked up by microphone(s), processed by feeding it through delays, filters and reverberators, and broadcast into the auditorium from several loudspeakers which may be at the front of the hall or distributed around the walls and ceiling. In an in-line system acoustic feedback (via the auditorium) between the loudspeakers and microphones is not required for the system to work (hence the term in-line). The PA and speech reinforcement systems described above are simple examples of in line systems.
The second type of assisted reverberation system is the non-in-line system in which a number of microphones pick up the reverberant sound in the auditorium and broadcast it back into the auditorium via filters, amplifiers and loudspeakers (and in some variants of the system, via delays and reverberators--see below). The rebroadcast sound is added to the original sound in the auditorium, and the resulting sound is again picked up by the microphones and rebroadcast, and so on. The non-in-line system thus relies on the acoustic feedback between the loudspeakers and microphones for its operation (hence the term non-in-line).
In turn, there are two basic types of non-in-line assisted reverberation system. The first is a narrowband system, where the filter between the microphone and loudspeaker has a narrow bandwidth. This means that the channel is only assisting the reverberation in the auditorium over the narrow frequency range within the filter bandwidth. An example of a narrowband system is the Assisted Resonance system, developed by Parkin advantage of such a system is that the loop gain may be relatively high without causing difficulties due to instability. A disadvantage is that a separate channel is required for each frequency range where assistance is required.
The second form of non-in-line assisted reverberation system is the wideband system, where each channel has an operating frequency range which covers all or most of the audio range. In such a system the loop gains must be low, because the stability of a wideband system with high loop gains is difficult to maintain. An example of such a system is the Philips which is installed in several concert halls around the world, such as the gain due to the MCR system is given by ##EQU1## where .alpha..sub.MCR is the loop gain and N is the number of microphone, loudspeaker channels. The reverberation time is increased by the same factor.
An improved wideband non-in-line assisted reverberation system has been 1) N microphones pick up the sound in the primary room and the microphone signals are fed into a secondary room and are reverberated and scaled by the loop gain before being fed back into the primary room. In practice the secondary room is replaced with a reverberation matrix. This improved system allows the apparent volume in the primary room to be altered independently of the apparent absorption. The improved system shall be denoted VRA (Variable Room Acoustics). The power gain introduced by the system is given by ##EQU2## where .alpha..sub.VRA is the loop gain. The expression contains
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Industrial Research Limited
Kuntz Curtis
Mei Xu
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