The spectrogram is the result of calculating the frequency spectrum of windowed frames of a compound signal. It is a three-dimensional plot of the energy of the frequency content of a signal as it changes over time.
Spectrograms are used to identify phonetic sounds, to analyse the cries of animals, and in the fields of music, sonar/radar, speech processing, etc. A spectrogram can also be called a spectral waterfall, sonogram, voiceprint, or voicegram. The instrument that generates a spectrogram is called a sonograph.
Spectrograms are usually created in one of two ways; either with a series of bandpass filters, or calculated from the time signal using the short-time Fourier transform (STFT).
How long is a minute depends on which side of the bathroom door you are on. (Albert Einstein)