1. Apparatus for digital signal processing, the apparatus comprising: a cascade of digital filters connected to receive a sampled input signal or samples from a data stream and having at least an output, in which the data stream is taken from the at least an output of the cascade of digital filters and in which the digital filters implement a transform decomposed into lifting steps; the cascade of digital filters being configured to operate on pairs of samples from the sampled input signal while leaving available idle cycles; and a multiplexer for multiplexing the samples of the data stream with the sampled input signal, the multiplexer being configured for interleaved processing of the samples of the data stream with the sampled input signal by the cascade of digital filters during the available idle cycles.