Spectrographs

Spectrographs are 3-D views of time-varying data and signals. A typical Spectrograph shows frequency on the vertical axis, time on the horizontal axis, and amplitude encoded as variations in color or gray-shading. Spectrographs are commonly used in situations where frequency of one or more signals tends to vary over time, and it's important to view clearly the amplitude, or "magnitude", of the variation. Audio, radio, astronomy, optics, and vibration are examples of scientific areas where spectrographs serve as an essential tool.

Spectrographs are normally generated from Fourier Transform results, either DFT (Discrete Fourier Transform) or FFT (Fast Fourier Transform).

Below are some examples of Signalogic spectrograph displays, taken from signal processing applications including voice compression, speech recognition, and fax relay.

Frequency domain (2-D spectrograph) and time domain (waveform display). Frequency shown on vertical axis, time on horizontal axis, and energy (amplitude) shown as color variation.	Frequency domain displays: a) Log Magnitude/Log Frequency, b) Waterfall (3-D Spectrogram), and c)2-D spectrograph ("Submarine Sonar view")
Waterfall (3-D Spectrogram) and 2-D Spectrograph Displays	Frequency domain (2-D Spectrograph) and time domain (waveform display/edit) graphs of pre-MELP speech data (trace 1) and MELP-processed speech data (trace 2).
Spectrograph showing facsimile (fax) communication between (i) two Brother machines, and (ii) a Sharp and HP machine. Note that CNG, CED, DIS, DCS, TCF, CFR, and data transmission tones have been labeled.