Echo prevention circuit having signal subtracter feature

A digital signal processing circuit comprising:

• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• and
• a third output terminal to which the signal through the second input terminal is output,
• wherein the first FIR filter and the second FIR filter have such filter coefficients that the signal output through the third output terminal has only the output signal from the first FIR filter removed or reduced.

A method of setting filter coefficients of an echo prevention circuit comprising:

• an input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• an input/output terminal to which an output signal of the first FIR filter is output or a second input signal is input;
• a subtracter that subtracts an output signal of the second FIR filter from a combined signal of the output signal of the first FIR filter and the second input signal;
• and
• an output terminal to which an output signal of the subtracter is output,
• the setting method which sets the first FIR filter and the second FIR filter to have such filter coefficients that the output signal through the output terminal has only the output signal from the first FIR filter removed or reduced.

A method of setting filter coefficients of a digital signal processing circuit comprising:

• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• and
• a third output terminal to which the signal through the second input terminal is output,
• the setting method which sets the first FIR filter and the second FIR filter to have such filter coefficients that the signal output through the third output terminal has only the output signal from the first FIR filter removed or reduced.

A recording medium storing a program for setting filter coefficients of an echo prevention circuit comprising:

• a processor;
• an input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• an input/output terminal to which an output signal of the first FIR filter is output or a second input signal is input;
• a subtracter that subtracts an output signal of the second FIR filter from a combined signal of the output signal of the first FIR filter and the second input signal;
• and
• an output terminal to which an output signal of the subtracter is output,
• the program which causes the processor to implement a function to set the first FIR filter and the second FIR filter to have such filter coefficients that the output signal through the output terminal has only the output signal from the first FIR filter removed or reduced.

A recording medium storing a program for setting filter coefficients of a digital signal processing circuit comprising:

• a processor;
• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• and
• a third output terminal to which the signal through the second input terminal is output,
• the program which causes the processor to implement a function to set the first FIR filter and the second FIR filter to have such filter coefficients that the signal output through the third output terminal has only the output signal from the first FIR filter removed or reduced.