Abstract: A noise-cancellation scheme in a system receiving acoustic information signals, where the system is carried in a vehicle having self-generated engine noise. An engine rotation sensor generates pulses driving a synchronous type filter device which passes only the engine noise frequency and its harmonics. The latter signal is then subtracted from the total input signal having information and noise combined. One filter circuit comprises a phase-locked loop with a multiplying counter whose output goes to a multiplexer having a plurality of grounded capacitors connected thereto.