Methods and apparatus for digitally signaling sounds and tones in a PCM multiplex system

摘要

Different ones of a plurality of sounds or tones are digitally signaled selectively in the different time slots of recurring frame cycles by initially storing a group of PCM samples for each sound in addressable memory. As each given time slot recurs one sample of a sound preselected for that time slot is read out to a common bus, and as successive cycles occur the address signals applied to the memory during any given time slot are progressively changed to cause repeated scanning of the samples of the preselected sound. After address signals for one time slot have been pulled from a read/write memory, they are replaced by writing "next sample address" signals into the same location of that memory, the latter having a word location for each time slot and being addressed for reading and writing by control signals which exist during and uniquely identify the successive time slots of each cycle. Different scan sequences for different sounds are created by modifying the formation of "next sample address" signals under the control of characteristic-representing signals stored in a sequence memory and read out by call signals representing the preselected sound for any time slot. The preselection permits any of the sounds to be placed in any of the time slots or channels, but in the preferred form some of the time slots always carry the same sounds (fixed tones) while others may have their carried tones ("switched" or register tones) changed by commands received asynchronously from a central control unit. The methods and apparatus utilize ROM (although RAM may be employed) to pair different ones of the several sounds with different ones of several on/off schedules to form a larger plurality of distinctive "tones", any one of which may be digitally signaled in any time slot or channel. The method and the apparatus permit some of the tones to be "intercept" tones formed by two sounds transmitted alternately with a predetermined duty cycle.