Abstract
Correlation techniques which use M-sequence signal are applied to some acoustic measurements. The band noise modulated (intermitted) by the M-sequence signal is emitted from the speaker. The microphone output after receiving the sound is squared and the cross-correlation of M-sequence signal and the squared signal is computed. Then we may be able to find from the correlation peaks the sound intensity and the acoustical delay time without the influence of external noise. If there are multiple sound paths from speaker to microphone, each sound ray can be measured separately by this method. These are the properties similar to those of the correlation measurement by white noise, but M-sequence method has the following advantages:1) The shape 00 the correlation function with delay time r is triangle, and the amplitude and the delay time of the correlation peak can be detected very easily. 2) The triangular form of the correlation function remains unchanged. if the frequencies of band noise are varied. This is because the shape of the correlation function depends only on the nature of the M-sequence signal, while the amplitude of the correlation peak depends on the properties of noise.
