Aki Mäkivirta

System for processing an audio signal so as to reduce the noise contained therein by monitoring the audio signal content within a plurality of frequency bands

The invention relates to a system for processing an audio signal to reduce the noise contained therein, the system comprising a source (1) of an audio signal in electric form, a first filter group (2) for dividing the audio signal into several subband signals in different frequency bands, a detector (3) for each subband signal to detect the audio signal level thereof, and a compressor/expander (4) for compressing/expanding each subband signal on the basis of the detected audio signal level thereof, and a second filter group (5) for combining the compressed/expanded subband signals to generate a reconstructed audio signal (6). According to the invention the first filter group (2,5) is arranged to divide the sound frequency range into bands with a width enabling the processing of the signal within the critical bands, and each compressor/expander (4) is arranged to attenuate the signal in its band when the detector (3) associated therewith has detected that the audio signal is missing from said frequency band.

Region of control for low frequency modal equalisation in small listening rooms

Small‐size listening rooms are characterized by sparse modal density with pronounced spectral colouration when the decay times at low frequencies are large. Various active approaches for reducing the modal decay time have been suggested in the literature. A review of the salient principles of these approaches is given. Active control of the modal decay time at the primary listening position by using the primary radiator for control is demonstrated and evaluated for performance. The locality and size of the region of control, and the amount of control achieved, are studied in light of the experiment. Effect of the modal equalizer filter to the perceived response flatness, audibility of low frequency resonances, and the required amount of modal equalization are discussed in light of the experiment.