A spectrogram is the graphic representation of the time course of the frequency spectrum of a signal . Spectrograms are widely used, for example for the purpose of analysis of sound signals , the signal processing and image processing or display of trace elements in the neutron activation analysis .
A spectrogram represents the composition of a signal (e.g. a sound or spoken language) from individual frequencies , usually over time. In this case, a spectrogram is, more precisely, a time-variant representation of the frequency distribution using the short-term Fourier transform . This results in a complex-valued function that depends on the time t and the frequency . The spectrogram is a representation that plots the values in a time-frequency diagram (for example color-coded).
The interpretation is that it indicates the frequency component of the signal at time t .
A sonagram (from Latin sonare ' to sound' and from ancient Greek γράφειν grafeïn , German ' to write' ) is a sound spectrogram. Originally, the sonagram and sonagraph were trade names : The sonagram was the representation of rapidly changing sound processes in rectangular coordinates (time and frequency axes) supplied by a sonagraph. The strength of the frequency components was made visible by blackening the recording paper. Today the term Sonagraf (or Sonagraph ) is used regardless of the make of the device. Nowadays, sound analysis is only carried out digitally, mostly with the help of computer programs.
Sonagrams are used, among other things, to analyze speech signals, e.g. B. to determine speech sounds ( phonetics ). Vowels can be recognized in the sonagram by characteristic patterns, the so-called formants . Consonants can be recognized, for example, by the course of the black coloration (depending on the intensity), by the existing or non-existing voice bar (a black bar in the lower area that shows the voicing ) and by various transitions.
In vehicle and machine acoustics, there is often a particular interest in the relationship between the spectrum and the engine speed . The spectral course of a high rev is therefore not shown as a function of the measurement time, but as a function of the speed. The term Campbell diagram is used for this form of the spectrogram .
- Uwe Kiencke , Michael Schwarz, Thomas Weickert: Signal processing. Time-frequency analysis and estimation methods . Oldenbourg, Munich 2008, ISBN 978-3-486-58668-8 .
- Online tutorial on reading sonograms
- Link to download a sonagram software ("praat")
- Collection of animated sonograms for works of electroacoustic music at INA