Companding is non – uniform Quantization. It is required to be implemented to improve the signal to Quantization noise ratio of weak signals.
The Quantization noise $= Nq=S^2/12.$
This shows that in the uniform Quantization once the step size is fixed, the Quantization noise power remains constant.
But the signal power is not constant. It is proportional to the square of signal amplitude. Hence signal power will be small for weak signals, but quantization noise power is constant.
Therefore the signal to Quantization noise rates for weak signals is very poor, this will affect the quality of the signal. The remedy is to use companding.
Companding = compressing + Expanding
Here, weak signals are amplified and strong signals attenuated before applying them to a uniform quantizer.
This process is called as “compression” and block provides it is called as a “Compressor “
At the receiver exactly opposite process is followed which is called expansion. The circuit used for providing expansion is called as an “expander”
The compression of signal at transmission and expansion at receiver is combined to be “companding”
- Analog Companding
- Digital Companding