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Companding

Telecommunications signals are seldom linearly encoded, but rather are companded [a combination of compression & expansion]. This allows for a more uniform S/N ratio over the entire range of signal sizes.

If the quantization step size is constant, the S/N ratio decreases for small signals. To prevent this, the step size varies according to the signal size.

Logarithmic Companding Curves

The telecom industry has used logs to measure acoustic and electrical signals. The most common is the dB unit.

North American -law and European A-law codecs perform the same function but with a slight difference in implementation..