The present invention relates broadly to a method of digitally filtering an audio signal by applying a composite audio filter. The composite audio filter may be obtained by applying one audio filter to another audio filter each having the same predetermined sample rate including neighbouring sample points. The other audio filter may also include one or more intervening sample points between adjacent of its neighbouring sample points. The one audio filter may be applied to the other audio filter at an adjusted sampling rate relative to the other audio filter. The adjusted sampling rate may be inversely proportional to the number of intervening sample points relative to the number of neighbouring sample points for the other filter. The frequency response curve for the composite filter derived using the adjusted sampling rate may be more indicative of an idealised lowpass filter. The frequency response with the adjusted sampling rate may display a more bell-shaped characteristic compared with the frequency response without an adjusted sampling rate (shown in broken line detail).