The signal-to- noise ratio(SNR) is the ratio of the power of the transmitted useful signal to the power of the noise signal and a measure of the purity of a signal. Since the ratio between the useful signal and the noise signal can be several powers of ten, the signal-to-noise ratio is specified on a logarithmic scale, namely in decibels( dB). The higher the signal-to-noise ratio, the more interference-free and less noisy the useful signal.
The signal-to-noise ratio, also referred to as the signal-to-noise ratio, is used in high- frequency technology, radio technology, measurement technology and acoustics and shows how strongly the useful signal is affected by noise in a communications transmission. It is also an important characteristic value for the dynamics of quadrupoles; such as amplifiers, A/D converters and microphones. This can only be as large as the SNR ratio, since otherwise the amplifier would already amplify the noise. If the signal-to-noise ratio is 1, then the average power of the noise is equal to that of the useful signal.
Improving the signal-to-noise ratio
The signal-to-noise ratio can be improved by certain measures. In addition to increasing the useful signal level, expander techniques are used in which useful signals with a low level are transmitted at a higher level before transmission and decompressed again afterwards. It is also possible to use filters that limit the noise signal above a certain frequency without affecting the useful signal. With A/D converters, the signal-to-noise ratio can be improved by higher sampling rates and quantizations with higher word widths.
In order to ensure speech intelligibility and voice recognition in transmission systems, speech signals are digitized with a word width of 8 bits in PCM technology. In optical transmission systems, the optical signal-to-noise ratio( OSNR) is used to evaluate the transmission characteristics.