Correlation meter
A correlation meter or visualization to goniometer or as stereo vision device called (SSG), English vectorscope is an electric meter in the sound equipment , the relations between the two channels (left and right) of a stereo - audio recording can be detected by measurement .
Basics
This phase indicator is only intended to control the coincidence stereophony with coincidence microphones , i.e. if there are only level differences and no transit time components, whereby the differences in the amplitudes (level) of the two channels are absolutely not used for evaluation. Errors such as the failure of a channel and reverse polarity stereo signals can also be detected.
For this purpose, the phase relationships of the two channels, that is, the equality or different nature of their signals, are related by means of the correlation . The representation can take place as a pointer representation ( r = cos ) or in graphical form like a goniometer. The graphical representation has the advantage that the information content can be better recognized.
The measurement is particularly important for assessing the mono compatibility of the material, since both channels are mixed together when a stereo signal is reproduced in mono. This is particularly important for music productions that are to run on the radio (still widespread use of mono devices, e.g. simple transistor and “kitchen” radios). In the case of opposing phase relationships, cancellations occur that negatively affect the sound image. In the extreme case of signals running in the opposite direction, the result of "mono listening" is silence.
The degree of correlation does not depend on the level ratio of the two signals. In the case of recordings with runtime stereophony, the degree of correlation is not particularly meaningful, since only simultaneous signals are compared. In spite of this, the degree of correlation will mostly be greater than zero here, since lower frequencies (i.e. larger wavelengths) are more closely correlated due to the less significant transit time differences.
Readings
The determined values mean the following:
| Degree of correlation | Explanation |
|---|---|
| +1 | Identical signals in both channels. This also creates a mono sound image on stereo equipment, as no different signals are reproduced. |
| between +1 and 0 | A (more or less) mono-compatible stereo signal is available. |
| 0 | Signals are very different or a channel is missing. |
| between 0 and −1 | There is a stereo signal that is not mono compatible. This means that the stereo signal cannot be used as a mono signal and is probably too quiet. |
| −1 | The signals are the same on both channels, but the polarity of the signal is reversed on one channel , e.g. B. as a result of interchanged connection lines in one of the two signal paths. No mono compatible stereo signal. |
literature
- Thomas Görne: Sound engineering . 1st edition. Carl Hanser Verlag, Leipzig 2006, ISBN 3-446-40198-9 .
- Hubert Henle: The recording studio manual . 5th edition. GC Carstensen Verlag, Munich 2001, ISBN 3-910098-19-3 .
- Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Manual of the recording studio technology . 8th edition. Verlag Walter de Gruyter, Berlin / Boston 2014, ISBN 978-3-11-028978-7 (2 volumes).
Web links
- Thoughts on the correlation meter (PDF; 33 kB)
- The degree of correlation - correlation of stereo signals and their display (PDF; 361 kB)
- How to read a correlation meter correctly ( memento of March 7, 2011 in the Internet Archive )