Digital mixing of audio data samples with a data clock whose frequency is based upon the number of paths defined through the mixer

An integrated circuit 39 is used for digital signal mixing of audio data samples from analogue and digital inputs 56, 62 to generate outputs 70, 74. The integrated circuit also includes a plurality of digital signal processing (DSP) blocks, which can act as data sources and data destinations. The digital mixing core 50 includes a multiply-accumulate block which takes data from one or more data source and, after any required scaling, generates output data for a data destination. Multiple signal paths can be defined by configuration data supplied to the device, either by a user, or by software. The multiply-accumulate block operates on a time division multiplexed basis clocked by a system clock whose frequency is controlled based upon the number of signal paths through the mixer to be less than that required to generate output data for every destination from every source. Multiple signal paths can be processed within one period of the sample clock. Each signal path has a respective sample clock rate, and paths with different sample clock rates can be routed through the multiply-accumulate block on a time division multiplexed basis independently of each other.