Gain, amplitude-dependent relative

If the density pc of the cell is known, then the acoustic velocity in the cell can be immediately deduced, since vc = Zc/pc. Since determination of acoustic velocity by this method depends on the measurement of relative amplitudes, the amplifiers and their gain controls must be accurately calibrated. The combination of reflection and transmission coefficients on the right-hand side of (9.4) can be expressed in terms of the acoustic impedances of the coupling fluid, the cell, and the substrate. 

Cross-correlation and spectral analysis have proven invaluable tools for quantifying the frequency dependent characteristics of the human subject. The cross-spectral density function, or cross-spectrum can be obtained from the random target x t) and random response y t) by taking the Fourier transform of the cross-correlation function r yfr), that is, Sxy(f) = F rxy z), or in the frequency domain via Sxyif) = X(f)Y(f), or by a nonparametric system identification approach (e.g., spa.m in Matiab ). The cross-spectrum provides estimates of the relative amplitude (i.e., gain) and phase-lag at each frequency. Gain, phase, and remnant frequency response curves provide objective measures of pursuit... 

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