Time Delay Spectrometry

Abstract

Human experience in the interpretation of sound strongly supports the concept of a time-dependent frequency spectrum. Acoustical testing of architectural structures must therefore be brought into alignment with joint time-frequency considerations to bridge the gap between subjective and objective performance assessment. Time delay spectrometry (TDS) is a method of measurement which directly yields the time-dependent frequency spectrum. This is done by transforming normal acoustic variables to a joint time-frequency coordinate system. By this means, acoustical properties that overlap in a pure-time or frequency domain measurement, as for example frequency-dependent multiple reflections, may be separated for analysis. Following separation of the signal of interest, the result is then transformed back to either the time or frequency representation for conventional evaluation, but with the difference that unwanted signals have been suppressed. Time delay spectrometry is a continuous coherent process that operates on a real-time basis allowing evaluation of system parameters in situ. The data obtained includes the complete response, both amplitude and phase, for either time or frequency. Measurements possible with TDS include direct and early sound anechoic spectra in a normally reverberant environment, reverberant energy as a continuous function of frequency and time, and joint time and frequency-dependent sound propagation through partitions.