Chirp-rate Estimation for Time-frequency Reassigned Spectrograms

Spectrogram analysis frequently suffers from inadequate time or frequency resolution, respectively. However, time-frequency reassigned spectrograms offer an attractive extension regarding the resolution trade-off. Specifically, this method deduces an improved time-frequency localization from the derivatives of the spectrogram phase, with respect to time and frequency. For high-quality images of reassigned spectrograms, however, there is a requirement for inconveniently short hop-sizes. Recently, the information of the cross-derivatives was introduced as local indicator for sinusoidal vs. impulsive signal characteristics. In this contribution, we try to extend the reassigned spectrogram points to lines, in order to allow for bigger hop-sizes. To this end, the second-order derivatives give coarse intermediate estimates of the chirp-rate. Using the cross-derivative indicator, we combine these intermediate estimates to a more accurate chirp-rate estimator. The properties of the novel time-frequency distribution is demonstrated in several examples.