IMPULSE REVERB CONVOLUTIONS

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Convolutions in Large Spaces

Two singers, mezzo-soprano Sue McGowan and bass Derrick Christian, are heard convolved with the impulse response (IR) of various churches. They now appear to be located at the same distance from the microphone as the original source, a balloon being burst. When they are convolved twice with the impulse response of the space, that distance doubles. No brightening of the output was used in these examples.

Shakespearean actor Christoper Gaze is also heard convolved with an IR of the Royal Drama Theatre in Stockholm. Although the reverb time is shorter, it is not what would be considered optimal for speech comprehension (i.e. less than one second). This is because the IR was made in an empty hall, without the absorption that would be created by an audience. This problem will be addressed in the main module.

Convolution with Impulse Response	Convolved Twice with Impulse Response
McGowan * Busseto	McGowan*Bus*Bus
McGowan * Santa Chiara
McGowan * San Francisco
McGowan * St Nikolai
McGowan * Temple
McGowan * Domkyrkan
DC low D*Busetto	DC lowD*Bus*Bus
Gaze * Theatre

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Convolutions in Smaller Spaces

Spaces where speech comprehension is paramount, such as theatres and most Protestant churches, need to have a smaller spatial volume and greater absorptive qualities in order to reduce the reverberation time to less than a second. Even without amplification, a speaker can also use a “projected” voice, such as heard here with actor Christopher Gaze, and speak more slowly and articulately. Compare these male examples in smaller churches (photos in the links) with a female voice, Thecla Schiphorst, that is speaking more intimately, but with great clarity.

Location	Male Voice	Female Voice
Old West Church
Trinity United
Old South Boston
Trinity Boston

Note: the reverberated sound (convolved with the impulse response) is mixed 50/50 with the original sound

Finally, what happens when you’d like to create an image of a space that you have no access to an impulse response? There are many sources of IR available online, but in the case of famous concert halls, such as the Concertgebouw in Amsterdam, you are unlikely to find a free sample of their acoustics. I don’t know if an IR can be copyrighted, but these institutions tend to keep their acoustic profile proprietary.

So, just as an experiment, here is a simulated IR from the Concertgebouw taken from the last second of a symphonic work that ends in a big climax (we won’t identify which one), as recorded in the Concertgebouw. Admittedly, it doesn’t quite fulfil the ideal IR as having equal energy in all frequency bands, but will it be close enough? In this case, we mixed the wet and dry signals appropriately to give a sense of distance. So, if you want to simulate your debut in a famous hall, this unorthodox technique may be just the thing!

The end of a recording in the Concertgebouw

Simulated performance in the same location