The Wavelet Analysis tool allows to post-process impulse responses and to create color plots of the energy of the signal versus time and frequency. The tool is similar to the ETF analysis described in chapter 12, but since it is based on wavelet transform instead of Fourier Transform, does not suffer from the fixed time-frequency resolution.
The ETF analysis is based on Short Time Fourier Transform (STFT). The idea behind STFT is to show the temporal evolution of the signal by means of the division of the signal itself into short sections and then Fourier Trasform every section. In this way the joint time-frequency evolution of the signal is highlighted. But at the same time the process lead to a fixed time and frequency resolution, due to the fact that time resolution is linked to section duration and frequency resolution is linked to FFT size.
The Wavelet Analysis tool implemented in CLIO uses a kernel of modified complex Morlet wavelets and can be interpreted as a constant Q analysis. Time resolution is high at high frequencies and frequency resolution is not too rough at low frequencies. This kind of analysis it is particulary suited for the inspection of wideband non stationary signals as the impulse responses of loudspeakers and rooms.
As a result of the Wavelet Analysis post-processing tool a matrix of coefficients is calculated. The magnitude squared of the coefficients is directly proportional to the energy of the signal in a domain located around a certain time and frequency. The magnitude squared of the Wavelet coefficients is depicted into a color plot called Scalogram: