Efficient Data Transformation in Time-Domain Spectrometry

In applications of time-domain spectrometry, in which frequency-domain information is obtained by means of Fourier transformation of time-domain excitation and response signals, results are often required at a number M of evenly spaced frequencies, where M is considerably smaller than N, the number of amplitude samples from which the discrete Fourier transform is formed. Under such conditions the modified form of fast Fourier transformation described offers markedly greater computing efficiency than the standard form.