Preto Paulo J., Martins C., Bento Coelho J.

The Swept Sine technique is becoming very popular for the measurement of room impulse response due to its large signal-to-noise ratio (SNR) and immunity against the non-linearities and time-variance of the room under test. However, the acoustical measurements in the presence of high level non-stationary noise usually reveal unsatisfactory results. Thus, the mean square of the overall sequence must be minimized in order to increasing the SNR. The Time Spectral Segmented Swept Sine technique consists in exciting the room with a set of M Swept Sine signals. Each frame is divided into N segments and analysed in the time-frequency domains followed by the estimation of the MS value of the respective segment. By using the average technique a weighting procedure is applied to each segment. This procedure ensures that the resulting Swept Sine signal has the highest SNR value. The filter bank used in the Time Spectral Segmented Swept Sine technique doesn’t explores the fact that with the increasing measurement time if the frame duration is greater than the impulse response length some of the sub-bands are not being excited yet. Keeping this in mind, the filter bank needs to be optimized in order to better remove the part of the spectrum that hasn’t signal test. Several examples are presented to compare the classic Swept Sine and the Time Spectral Segmented Swept Sine techniques with optimized filter bank giving advantages and disadvantages of each technique.