Fast filtering means and filtering and decimation methods

Hardware implemented decimation method for decimating a time-quantized pulse width modulated input signal comprising:

• dividing said time-quantized input signal into intervals, for each of said intervals establishing a sample of a time- and amplitude-quantized pulse code modulated output signal by performing filtering on the basis of at least a part of a filter representation and a representation of a derivative of at least a part of said input signal;
• whereby said performing filtering is arranged to omit arithmetic operations involving such samples of said representation of the derivative of at least a part of said input signal that are derived from identically valued continguous samples of said time-quantized input signal.

A filter arrangement comprising:

• a differentiator for establishing a representation of a derivative of at least a part of a time-quantized pulse width modulated input signal, and
• a filtering unit for establishing at least one sample of pulse code modulated output signal by performing filtering on the basis of at least a part of a filter representation and said representation of the derivative of at least a part of said input signal;
• wherein said filtering unit is arranged to omit arithmetic operations involving such samples of said representation of the derivative of at least a part of said input signal that are derived from identically valued contiguous samples of said time-quantized input signal.