A signal processing device, comprising: a subtractor that is configured to subtract a feedback signal from an input signal that is a digital audio signal and to output a first digital signal; a signal processing circuit that is configured to perform signal processing on the first digital signal and to output a second digital signal; a power amplifier circuit that is configured to amplify the second digital signal, to output the second digital signal amplified into an analog signal, and to output the analog signal; an A/D converter that is configured to convert the analog signal into a third digital signal and to output the third digital signal; an offset adjuster that is configured to adjust a DC offset for the third digital signal; an amplitude adjuster that is configured to adjust an amplitude for the third digital signal; a delay adjuster that is configured to adjust a delay of the second digital signal; and a calculator that is configured to extract a difference signal which is a difference between the third digital signal having the DC offset adjusted by the offset adjuster and the amplitude adjusted by the amplitude adjuster and the second digital signal having the delay adjusted by the delay adjuster, and outputs the feedback signal based on the difference signal, wherein the offset adjuster is configured to adjust the DC offset using a first parameter regarding the DC offset determined based on an output of the offset adjuster which is output when no signal is input to the signal processing circuit by the subtractor, the amplitude adjuster is configured to adjust the amplitude using a second parameter regarding the amplitude determined based on (i) an output of the amplitude adjuster which is output when the input signal and the feedback signal are not input to the subtractor and a first test signal is input to the signal processing circuit and (ii) the first test signal, and the delay adjuster is configured to adjust the delay using a third parameter regarding the delay determined based on the difference signal when the input signal and the feedback signal are not input to the subtractor and a second test signal is input to the signal processing circuit. a subtractor that is configured to subtract a feedback signal from an input signal that is a digital audio signal and to output a first digital signal; a signal processing circuit that is configured to perform signal processing on the first digital signal and to output a second digital signal; a power amplifier circuit that is configured to amplify the second digital signal, to output the second digital signal amplified into an analog signal, and to output the analog signal; an A/D converter that is configured to convert the analog signal into a third digital signal and to output the third digital signal; an offset adjuster that is configured to adjust a DC offset for the third digital signal; an amplitude adjuster that is configured to adjust an amplitude for the third digital signal; a delay adjuster that is configured to adjust a delay of the second digital signal; and a calculator that is configured to extract a difference signal which is a difference between the third digital signal having the DC offset adjusted by the offset adjuster and the amplitude adjusted by the amplitude adjuster and the second digital signal having the delay adjusted by the delay adjuster, and outputs the feedback signal based on the difference signal, wherein the offset adjuster is configured to adjust the DC offset using a first parameter regarding the DC offset determined based on an output of the offset adjuster which is output when no signal is input to the signal processing circuit by the subtractor, the amplitude adjuster is configured to adjust the amplitude using a second parameter regarding the amplitude determined based on (i) an output of the amplitude adjuster which is output when the input signal and the feedback signal are not input to the subtractor and a first test signal is input to the signal processing circuit and (ii) the first test signal, and the delay adjuster is configured to adjust the delay using a third parameter regarding the delay determined based on the difference signal when the input signal and the feedback signal are not input to the subtractor and a second test signal is input to the signal processing circuit.