Editing Spectrogram (section)

{{short description|Visual representation of the spectrum of frequencies of a signal as it varies with time}}
{{redirect|Sonograph|the musical recording|Sonograph (EP)}}
{{for|the scientific instrument|Optical spectrograph}}
[[Image:Spectrogram-19thC.png|thumb|upright=1.35|Spectrogram of the spoken words "nineteenth century".  Frequencies are shown increasing up the vertical axis, and time on the horizontal axis. The legend to the right shows that the color intensity increases with the density.]]
[[File:3D battery charger RF spectrum over time.jpg|thumb|upright=1.35|A 3D spectrogram: The RF spectrum of a battery charger is shown over time]]

A '''spectrogram''' is a visual representation of the [[spectral density|spectrum]] of [[frequencies]] of a signal as it varies with time. 
When applied to an [[audio signal]], spectrograms are sometimes called '''sonographs''', '''voiceprints''', or '''voicegrams'''. When the data are represented in a 3D plot they may be called ''[[waterfall display]]s''.

Spectrograms are used extensively in the fields of [[music]], [[linguistics]], [[sonar]], [[radar]], [[speech processing]],<ref>JL Flanagan, Speech Analysis, Synthesis and Perception, Springer- Verlag, New York, 1972</ref> [[seismology]], [[ornithology]], and others. Spectrograms of audio can be used to identify spoken words [[phonetics|phonetic]]ally, and to analyse the [[Animal communication|various calls of animals]].

A spectrogram can be generated by an [[optical spectrometer]], a bank of [[band-pass filter]]s, by [[Fourier transform]] or by a [[wavelet transform]] (in which case it is also known as a '''scaleogram''' or '''scalogram''').<ref>{{Cite journal|last1=Sejdic|first1=E.|last2=Djurovic|first2=I.|last3=Stankovic|first3=L.|date=August 2008|title=Quantitative Performance Analysis of Scalogram as Instantaneous Frequency Estimator|journal=IEEE Transactions on Signal Processing|volume=56|issue=8|pages=3837–3845|doi=10.1109/TSP.2008.924856|bibcode=2008ITSP...56.3837S|s2cid=16396084|issn=1053-587X}}</ref>
[[Image:Scaleogram.png|thumb|250px|Scaleograms from the [[discrete wavelet transform|DWT]] and [[continuous wavelet transform|CWT]] for an audio sample]]

A spectrogram is usually depicted as a [[heat map]], i.e., as an image with the intensity shown by varying the [[colour]] or [[brightness]].