Electrical audio signal processing systems and devices – One-way audio signal program distribution – Public address system
Patent
1985-12-09
1988-04-05
Ng, Jin F.
Electrical audio signal processing systems and devices
One-way audio signal program distribution
Public address system
381 71, 381 86, 381 94, 455113, H04R 302
Patent
active
047364327
ABSTRACT:
A notch filter as disclosed which is adaptable to notching out a background siren from voice communications from an emergency vehicle. Two embodiments are disclosed. In the first embodiment, a frequency lock loop tracks the fundamental frequency of an electronic siren. The siren fundamental frequency is then notched out from voice transmissions using a notch filter. In the preferred transmissions using a notch filter. In the preferred embodiment, a digital ramp is generated by a first digital signal processor. This signal is input to an amplifier and a speaker thus producing an electronic siren. The digital ramp is also input to a second digital signal processor which notches out the fundamental frequency and odd harmonics thereof from the digital ramp thus acting as a comb notch filter. Analog voice is digitized by way of an analog to digital converter and input to the second digital signal processor. The second digital signal processor combs out the fundamental frequency and odd harmonics of the background siren signal from the digitized voice signal. The digitized voice signal is then converted back to an analog signal by way of a digital to analog converter.
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Motorola Inc.
Ng Jin F.
Roney Edward M.
Schroeder L. C.
Southard Donald B.
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