Spectrogram
Definition
A visual representation of the frequency content of an audio signal over time.
A spectrogram displays how the frequency content of an audio signal changes over time. It is computed by dividing the signal into short overlapping windows and computing the Fourier transform of each window (a process called the Short-Time Fourier Transform or STFT).
The result is a 2D representation where the x-axis is time, the y-axis is frequency, and the color or brightness indicates amplitude or power at each time-frequency point. Spectrograms make speech patterns visually apparent — you can see formants, voiced vs. unvoiced sounds, and even read certain phonemes from the image. Mel spectrograms apply additional perceptual scaling to better match human hearing.