This example compares a chirp generated by sp_filters() to a chirp with identical parameters generated by make_filters(); the output is shown in Figure . The chirp generated by sp_filters() is transformed to the time domain, and the two chirps are superimposed on one graph. Includes/compare_chirps.tex Note that to get the graph to show both chirps as simultaneous functions of time, sp_filters() needed to know the coalescence time found by make_filters(), so the latter function is called first. If the coalescence time input to sp_filters() had been zero , its chirp would have finished at the beginning--or equivalently, the end--of the time-domain data.
Also note that the inverse realft() of the stationary phase chirp had to be multiplied by a factor to be comparable to the time-domain chirp. The 2/LENGTH factor is left out of the inverse realft(), and the SRATE factor is needed to keep the dimensions right. (Also, the forward realft() of the time-domain chirp would need to be multiplied by 1/SRATE to compare to the stationary phase chirp.)