A signal processing device comprising at least one control unit arranged to receive at least one pack-insert instruction, decode the received at least one pack-insert instruction, and output at least one pack-insert control signal in accordance with the received pack-insert instruction. The signal processing device further comprising at least one pack-insert component arranged to receive at least a first data block to be inserted into a sequence of data blocks to be output to at least one destination register, receive a plurality of further data blocks to be packed within the sequence of data blocks to be output to the at least one destination register, arrange the at least first data block and the plurality of further data blocks into a sequence of data blocks based at least partly on the at least one pack-insert control signal, and output the sequence of data blocks.