Effective measurement method for reverberation time using a constant signal-to-noise ratio swept sine signal

Abstract

Graduate School of Engineering, Tokyo Denki University,5 Senju-Asahi-cho, Adachi-ku, Tokyo, 120–8551 Japan(Received 10 October 2014, Accepted for publication 21 November 2014)Keywords: Reverberation time, Impulse response measurement, Swept sine, Signal-to-noise ratioPACS number: 43.58. e, 45.58.Gn, 43.60. c [doi:10.1250/ast.36.344]1. IntroductionReverberation time is a basic characteristic of roomacoustics, which is calculated from the impulse response (IR)of the room. In the measurement of reverberation time fromthe IR, a high signal-to-noise ratio (SNR) is required overa wide frequency band. In a previous paper, the authorsproposed the use of a constant signal-to-noise ratio sweptsine (CSN-SS) signal that provides a constant SNR of themeasured IR over the frequency band of interest [1,2]. In thispaper, the authors propose an effective measurement methodfor reverberation time using the CSN-SS signal.2. Control of SNR using CSN-SS signalFigure 1 shows the principle of IR measurement in thefrequency domain. HðkÞ is the transfer function of a targetsystem, which is the Fourier transform of IR, where k is thediscrete frequency number, although it is omitted in Fig. 1 forsimplicity. HðkÞ can be measured using a measurement signalSðkÞ, such as a swept sine signal. The noise componentexpressed as NðkÞ=SðkÞ is included in the measurement result,where NðkÞ is an environmental noise added to the systemoutput.The SNR of this result is the power ratio of HðkÞ toNðkÞ=SðkÞ:SNRðkÞ¼jHðkÞj