Vehicle internal noise reduction system and the method thereof

A vehicle internal noise reduction system for reducing an internal noise generated from a noise source having, an adaptive filter responsive to a noise signal picked up from said noise source for generating a canceling signal based on a tap number, a speaker responsive to said canceling signal for generating a canceling sound to cancel said internal noise in a passenger compartment, a microphone provided in said passenger compartment for receiving said internal noise and said canceling sound and for outputting an error signal as a result of a difference of said canceling sound and said internal noise, a transmission characteristic compensation section for generating a compensation signal to compensate a transmission characteristic of a propagation path between said adaptive filter and said microphone, and a tap value updating section for updating said tap value based on said compensation signal and said error signal and for transmitting said updated tap value to said adaptive filter, comprising:

• synchronizing pulse generating means responsive to said noise signal for generating a synchronizing pulse synchronized with a period of said noise signal;
• pulse interval detecting means for detecting an interval of said synchronizing pulse generated;
• tap number switching means responsive to said interval for generating a cut-off number equal to a number of sampling pulses within said interval and for generating a signal of said cut-off number;
• filter coefficients recording means for recording a filter coefficient to cut a specific frequency domain contained in said canceling signal;
• convolution means for convoluting said filter coefficient into said tap value of said adaptive filter up to a number of times equal to said cut-off number and for out-putting said convoluted tap value to said tap value updating section so as to shorten a number of times of calculations for convolution;
• and
• driver means responsive to said signal of said cut-off number for driving said convolution means each time when said period of said noise is changed.