Digital synthesis of analog signals for audiometric applications

This paper presents a novel signal generator, based on the direct digital synthesis (DDS) technique, which fulfills the requirements of advanced audiometric systems. The described solutions face two different problems, namely the generation of a finely tunable pure sinewave and the generation of noise signals with controlled spectrum. In order to achieve tuning capabilities down to 1Hz at 20 kHz or 15 μHz at 100 Hz, a fractional division of a 40 MHz master clock with noise shaping of the resulting error is performed. Moreover, for noise generation a novel circuit based on pseudo-random sequences combined with analog SC filters is used