Apparatus and Method for Setting Filter Coefficient, and Recording Medium Having a Program Recorded Thereon

A filter coefficient setting method of an echo preventing circuit having

• a first FIR filter that is inputted with a first digital signal and that outputs a second digital signal,
• a second FIR filter that is inputted with the first digital signal at the same time that the first FIR 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 method comprising the steps of:
• acquiring a first response signal of a section from an output of the first FIR filter to an output of the AD converter by generating a first signal;
• adjusting the magnitude of the first signal in response to the magnitude of the first response signal;
• acquiring again the first response signal;
• setting the filter coefficients of the second FIR filter based on the first response signal acquired again;
• setting the filter coefficients of the first FIR filter based on a second response signal of a section from an output of the second FIR filter to an output of the AD converter;
• and
• adjusting 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.

A recording medium having recorded thereon a program to set filter coefficients of an echo preventing circuit having

• a processor,
• a first FIR filter that is inputted with a first digital signal and that outputs a second digital signal,
• a second FIR filter that is inputted with the first digital signal at the same time that the first FIR 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 the 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 program being operable to cause the processor to implement the functions of:
• acquiring a first response signal of a section from an output of the first FIR filter to the AD converter by generating a first signal;
• adjusting the magnitude of the first signal in response to the magnitude of the first response signal and acquiring again the first response signal;
• setting the filter coefficients of the second FIR filter based on the first response signal acquired again and setting the filter coefficients of the first FIR filter based on a second response signal of a section from an output of the second FIR filter to an output of the AD converter;
• and
• adjusting 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.