Adaptive delta modulation for speech synthesis

The three most important factors in choosing a speech output processing method for a particular application are flexibility, bit rate and cost. Flexibility enables the user to change the binary speech patterns according to his needs; bit rate is the amount of binary information necessary to produce a certain length (I s) of continuous speech; and cost includes not only the LSl chip itself, but also the development tools necessary to produce the desired speech patterns. This design note presents a method called adaptive delta modulation (ADM) implemented on the 2920 signal processor and applied on iRMX 80 as a speech output module. It is highly flexible, has a bit rate one-twelfth that of ordinary PCM and requires low development cost. Its high flexibility is aue to the fact that the 2920 is used as a two-way (input and output) ADM preprocessor which is software selectable on the iRMX 80 side (Figure I), enabling the whole system to act as a binaryrecorder. Speech patterns can be modified just as in ordinary tape recorders without the slow access problem inherent in linear tape memory. Moreover, the input capability allows the user to do his own speech research