The Impact of Sound Control Room Acoustics on the Perceived Acoustics of a Diffuse Field Recording

Live recordings of music and speech in concert halls have acoustical properties, such as reverberation, definition, clarity and spaciousness. Sound engineers play back these recordings through loudspeakers in sound control rooms for audio CD or film. The acoustical properties of these rooms influence the perceived acoustics of the live recording. To find the practical impact of ‘room in room’ acoustics in general, combinations of random room acoustic impulse responses using convolution techniques have been investigated. To find the practical impact of a sound control room on the acoustical parameter values of a concert hall when played back in that control room, combinations of concert hall impulse responses and sound control room impulse responses have been investigated. It is found that to accurately reproduce a steady sound energy decay rate (related to the reverberation time), the playback room should have at least twice this decay rate, under diffuse sound field conditions. For energy modulations (related to speech intelligibility) this decay rate should be more than four times higher. Finally, initial energy ratios (related to definition and clarity) require auditive judgement in the direct sound field. ITU-recommendations used for sound control room design are sufficient for reverberation and speech intelligibility judgement of concert hall recordings. Clarity judgement needs a very high decay rate, while judgement of spaciousness can only be done by headphone.