Digital wave generator for composite tone

摘要

Digital words defining magnitude levels of samples of phases of a wave cycle are stored in two memories arranged to store samples of 440 Hz and 480 Hz tones. The words are read out of the memories in a predetermined order which defines successive phases of the wave cycles, each word being read out a plurality of times before the next successive word is read to increase the sample rate without increasing the number of stored words. The words are converted to the defined levels to form step waves corresponding to the two tones and summed and the resultant composite wave is integrated to form a relatively smooth composite tone (ringback) signal.