Patent ID: 7945058

Claim:
A noise reduction system used in a BTSC (Broadcast Television System Committee) system to reduce noise of an audio signal z during an encoding process prior to digital processing, the noise reduction system comprising an audio spectral compressing unit including: a filter arranged to filter an input signal according to a transfer function, H(z), having a plurality of parameters, wherein the plurality of parameters are determined based upon a variable d equal to 20 log X, wherein X is the time-weighted root mean square of the encoded audio signal z; and a memory configured to output parameters b 0 /a 0 , b 1 /b 0 and a 1 /a 0 to the transfer function when a value of d is greater than 0, and output parameters a 0 /b 0 , b 1 /b 0 and a 1 /a 0 when the value of d is less than 0; wherein when the value of variable d is greater than 0, the transfer function is: H ⁡ ( z ) = b 0 a 0 × 1 + b 1 b 0 ⁢ z - 1 1 + a 1 a 0 ⁢ z - 1 and when the value of variable d is less than 0, the transfer function is: H ⁡ ( z ) = a 0 b 0 × 1 + a 1 a 0 ⁢ z - 1 1 + b 1 b 0 ⁢ z - 1 .