What it does
Noise reduction using IIR digital filter..
Illustrates the use of the computationally-efficient IIR (recursive) filter for broad-band noise rejection. In this example, a signal generator is used to artificially add excessive noise to the audio signal. (A band-pass filter is employed to limit the bandwidth of the noise.) A band-stop filter (tuned roughly to the noise characteristics) is used to filter out the noise from the combined signal. Experiment with the filter settings to explore the filter behaviour. (Compare with the unprocessed noisy signal by momentarily connecting the output of the mixer directly to the output device).
It is instructive to observe that when the noise and the signal share the same frequency band, it is more difficult to filter out the noise without adversely affecting the signal. This is an important lesson in the art of filtering.
See also the "NoiseReductionBySpectralSubtraction1.dwb", "NoiseReductionBySpectralSubtraction2.dwb" "NoiseReductionBySpectralSubtraction3.dwb", "NoiseReductionBySpectralSubtraction4.dwb" and "NoiseReductionBySpectralSubtraction5.dwb" example DrawingBoards for more elaborate noise reduction implementations based on the power technique of spectral subtraction.