Conversion between analogue and digital signals

Analogue to digital (A/D) and digital to analogue (D/A) converters perform the required conversion at a higher sampling rate (e.g. 64Fs) and a lower resolution (e.g. 1 to 4 bits) than the actual sampling rate (Fs) and resolution (e.g. 16 bits) of the required digital signal. The oversampled low resolution signal is generated by oversampling the input digital signal (for D/A conversion) or is decimated, 20, to generate the required output digital signal (for A/D conversion). The oversampling or decimation filters are switchable between two modes of operation, in which different signal delays are imposed by the filter. Thus a lower quality, but shorter delay, filter can be used in converters in the signal path for an artist's foldback signal. This can reduce the subjectively disturbing effects of long conversion delays in the foldback signal path. A plurality of audio channels may be processed eg for recording, by apparatus which is operable in at least a first mode in which Nö channels are processed at a sample rate of Fs1, and a second mode in which N2 channels are processed at a sample rate of Fs2, where the product of N1 and Fs1 is equal to the product of N2 and Fs2. Specifically N1 = 2N2 and 2Fs1 = Fs2.