Audio Noise Reduction System
Harry F. Olson · The Journal of the Acoustical Society of America · 1948
A threshold type of noise reduction system has been developed for use in reducing the noise in sound reproducing systems. A non-linear element allows the useful signal to pass but discriminates against the noise. This system lowers the ground noise level and thereby increases the signal-to-noise ratio without discrimination against the useful part of the signal. The operation of the system is instantaneous. There is no frequency discrimination for any signal level above the threshold.