Spectral and perceptual properties of a transfer chain of two rooms

Invited paper

Carl v. Ossietzky University Oldenburg

Wednesday 3 june, 2015, 09:00 - 09:20

0.9 Athens (118)

Abstract:

This work examines the perceptual properties of the transfer chain of a recording room and a playback room. Recordings in a room have acoustical properties that can be measured with a room impulse response (RIR). Assuming the user reproduces these recordings over loudspeakers in another "playback"- room, the acoustical properties of that playback room will also influence the sound field. Mathematically this playback chain can be expressed as a convolution of two RIRs. In an analytic comparison, the double convolution of these two RIRs is analyzed and compared to the single RIR. The double convolution leads to an extended reverberant tail and to fundamental changes in the shape of both the reverberant tail and onset of the RIR.
These changes can further be analyzed in the frequency domain. A statistical property of a single room above the Schroeder Frequency is a fixed standard deviation (STD) of the logarithmic magnitude spectrum of 5.57 dB.
The convolution of two RIRs in the time domain leads to a multiplication in the spectral domain, while the logarithmic presentation leads to an addition of the logarithmic magnitude spectrum. Thus the resulting STD is a combination of the single STDs. As a result the playback chain involving two rooms leads to an increase in spectral fluctuation strength, measured by the STD of the logarithmic magnitude which increases by a factor of square-root of two.
A listening test confirmed that this increase in STD leads to a perceptible change in coloration.