1. Apparatus for digital signal processing, the apparatus comprising: a cascade of digital filters connected to receive a sampled input signal and samples from a data stream and having an output, in which the digital filters implement a transform decomposed into lifting steps, the cascade of digital filters operating on pairs of samples from the sampled input signal and the data stream; and a multiplexer for multiplexing the samples of the data stream with the sampled input signal for processing by the cascade of digital filters.