This paper provides a computationally efficient noise filtering technique for reducing stepper motor noise energy in a Digital Still Camera application without significantly altering the speech signal energy. The filtering technique uses a cascade of bi-quadratic filters to improve the signal-to-noise ratio by reducing
noise energy.

The noise filter described in this paper uses an Automatic Gain Controller stage to maintain signal energy when the noise filter is active. Such a filter achieves about 10 dB PSNR improvement at 2 MHz of ARM9 processor load. Furthermore, the paper briefly explores the filter structure for efficient hardware or software realization.