Input and output sections of an analog-to-digital converter are joined by an interface. In the input section, an analog input signal is converted to a multi-bit digital signal before being converted, by a noise-shaping converter such as a sigma-delta modulator, to a lower bit signal. The lower bit signal is carried across the interface before being converted, by a digital filter to recover the original multi-bit signal. The same principle is applied to the input and output sections of a digital-to-analog converter.