Patent ID: 7420488

Claim:
A filter coefficient setting apparatus that sets filter coefficients of an echo preventing circuit having a first Finite Impulse Response filter that is inputted with a first digital signal and that outputs a second digital signal, a second Finite Impulse Response filter that is inputted with the first digital signal at the same time that the first Finite Impulse Response filter is inputted with the first digital signal, and that outputs a third digital signal, a first DA converter that converts the second digital signal into a first analog signal and outputs the first analog signal, a second DA converter that converts the third digital signal into a second analog signal and outputs the second analog signal, an input/output terminal that outputs the first analog signal or that is inputted with a third analog signal, a subtracting circuit that outputs a fourth analog signal obtained by subtracting the second analog signal from a signal formed by combining the first analog signal and the third analog signal, and an AD converter that converts the analog signal outputted from the subtracting circuit into a digital signal and outputs the digital signal, the apparatus comprising: a response signal acquiring unit that acquires a first response signal of a section from an output of the first Finite Impulse Response filter to an output of the AD converter by generating a first signal, adjusts the magnitude of the first signal in response to the magnitude of the first response signal, and acquires again the first response signal; a filter coefficient setting unit that sets the filter coefficients of the second Finite Impulse Response filter based on the first response signal acquired again and sets the filter coefficients of the first Finite Impulse Response filter based on a second response signal of a section from an output of the second Finite Impulse Response filter to an output of the AD converter; and a signal level adjusting unit that adjusts the signal levels of the first and the second analog signals based on the amount by which the level of the first signal is to be adjusted such that the fourth analog signal is a signal obtained by removing or attenuating the first analog signal from a signal formed by combining the first analog signal and the third analog signal.