A Comb-Filtered Noise Generator for Use in Auditory Neurophysiological and Psychophysical Experiments

A digital CMOS comb-filtered noise generator has been developed for use as a stimulus in auditory physiological and psycho-physical experiments. It incorporates two identical, 34-bit shift register pseudo-random noise generators whose outputs are summed and low-pass filtered. By introducing a delay between the generators, a noise power spectrum results which is co-sinusoidal on a linear frequency scale (i.e., "comb-filtered"). The generator may be operated either manually or automatically with a range of delays of 1 Ps or greater, selectable in 1 ps increments. The polarity of one of the shift registers may be changed to produce an inverted output spectrum. The peak-to-valley ratio of the spectrum is adjustable in discrete steps over the range from 0 to 35 dB. The output noise is low-pass riltered at 50 kHz, and has Gaussian amplitude characteristics to 3 a.