A graph of the variation of spectral shape as a function of time. A spectrogram has three axes: the horizontal axis represents time, the vertical axis represents frequency and the density of marking represents the intensity of the signal at a particular time-frequency co-ordinate. Spectrograms are divided into two varieties, depending on the bandwidth of the analysing filter: (1) wide-band (usual filter bandwidth=300 Hz) which gives good resolution in the time domain (2) narrow-band (usual filter bandwidth=45 Hz) which gives good resolution in the frequency domain.
The two images below show a wide-band and a narrow-band spectrogram of the phrase Speech Internet Dictionary.
Also called sonagram and voiceprint.