Patent ID: 7468687

Claim:
A signal processing device, comprising a first digital signal processing block and a second digital signal processing block, wherein: the first digital signal processing block comprises: first gain adjustment means to which a digital signal subjected to predetermined digital signal processing is input and from which the digital signal is output after a gain according to a set gain value is given to the digital signal; and first digital to analog conversion means for converting the digital signal output from the first gain adjustment means to an analog signal and outputting the analog signal from the first digital signal processing block, the second digital signal processing block comprises: analog to digital conversion means for converting the analog signal output from the digital to analog conversion means of the first digital signal processing block to a digital signal; digital signal processing means for subjecting the digital signal output from the analog to digital conversion means to predetermined digital signal processing; second gain adjustment means to which the digital signal output from the digital signal processing means is input, from which the digital signal is output after a gain according to a set gain value is given to the signal, and to which gain sensitivity lower than that of the first gain adjustment means is set; and second digital to analog conversion means for converting the digital signal output from the second gain adjustment means to an analog signal and outputting the analog signal from the second digital signal processing block, the first digital to analog conversion means and the analog to digital conversion means are set such that a relation, in which the minimum value within a range of dispersion of the errors of the signal level in the first digital to analog conversion means is equal to or larger than the maximum value within a range of dispersion of the errors of the signal level in the analog to digital conversion means, and the signal processing device further comprises: detection means for detecting the level value of the digital signal output from the second gain adjustment means; first gain set means for setting a gain value to the first gain adjustment means such that the level value detected by the detection means is set to a maximum value within a range less than a prescribed value in a state that a signal whose level is treated as a maximum value in the first digital signal processing block is input to the first gain adjustment means; and second gain set means for setting a gain value to the second gain adjustment means such that the level value detected by the detection means is set to a maximum value within a range equal to or less than the prescribed value in a state that a signal whose level is treated as a predetermined maximum value is input to the first digital signal processing block after the gain value is set by the first gain set means.