In order to simplify a speech synthesizer arrangement concurrently with improvement of operation flexibility thereof, a digital memory is arranged to store at least one voiced sound source and at least one unvoiced sound source. One of the sound sources is selected in accordance with the content of a first register, while the data within the selected source is specified by the content of a shift register sequence generator. Each of the bit patterns obtained at the shift register sequence generator is compared with the content of a second register. In the event that the contents of the sequence generator and the second register coincide, the shift register sequence generator is reset and/or the operating conditions(s) of the synthesizer is changed.