a digital signal processing apparatus for converting an analog signal to a digital signal and digitally processing the digital signal is disclosed . the apparatus includes a modulation part for performing pulse density modulation on the analog signal and outputting a pulse density modulation signal , a memory for storing a conversion program for converting the pulse density modulation signal to pulse code modulation data , and a cpu for receiving the pulse density modulation signal from the modulation part and converting the received pulse density modulation signal to pulse code modulation data according to the conversion program stored in the memory .