Signal processors

An audio signal processing system comprising a plurality of Delta-Sigma Modulators (DSM) arranged in series, at least one of the Delta-Sigma Modulators being an nth order Delta-Sigma Modulator where n is at least 3, the DSM having

• an input for receiving a 1-bit signal,
• a quantizer for requantizing a p-bit signal to 1-bit form, a requantized signal being an output signal of a processor, and
• a plurality of signal combiners including:
• a first combiner for forming an integral of an additive combination of a product of the input signal and a coefficient and of a product of the output signal and a coefficient,
• at least two intermediate combiners each for forming an integral of an additive combination of a product of the input signal and a coefficient and of a product of the output signal and a coefficient, and of an integral of a preceding stage, and
• a final combiner for forming an additive combination of a product of the input signal and a coefficient and of the integral of the preceding stage to form the p bit signal which is requantized by the quantizer, to form the 1-bit output signal,
• wherein the coefficients are chosen to provide an overall attenuation of the input signal and a quantization noise, and also to provide a low pass filter which provides a gain to the input signal which compensates for the attenuation;
• and
• wherein said coefficients are fixed and a separate adder is provided in an integrator to enable sums of outputs of coefficient multipliers to be replaced by a look-up table, whereby said look-up table stores all combinations of said coefficient multipliers addressed by said 1-bit signals.