Accuracy of frequency estimates using the phase vocoder

The phase vocoder is a well-known technique for dividing an audio signal into time-varying sinusoidal components and estimating their frequencies and amplitudes. The accuracy of the frequency estimates is studied here by predicting, and then measuring experimentally, the magnitude of errors due to two factors: (1) interference between different components, and (2) interference due to the presence of noise in the signal. The magnitude of the error depends an the relative amplitudes of the component in question and the disturbing signal, on the size and spacing of the analysis windows, on the window function used, and, in the case where the disturbance is due to another sinusoidal component, on the phase difference between the two. The implications of these results for choosing analysis parameters are discussed. The case of a one-sample spacing between analysis windows is treated in detail. Finally, we compare the phase vocoder with the maximum likelihood frequency estimator.