A spectrogram is a visual representation of the frequency content of a signal over time. It is a plot that displays the intensity of different frequencies of a signal as they change over time, typically represented as a heat map or color map. The spectrogram represents the energy of the [[short-time Fourier transform (STFT)]] with the amplitudes in [[deciBel]]s: $ S(n,k) = 20 \log_{10}|X(n,k)| $ where, $n$ is the index of time, $k$ of frequency, $X(n,k)$ the STFT of the signal, and $S(n,k)$ the bi-dimensional image known as the spectrogram. When representing speech signals the spectrogram axis are converted to continuous time and frequency values. ![[Spectrogram_and_the_STFT_8_0.png]] [[Backstrom 2022]]