Browse Prior Art Database

Digital Tone Generation

IP.com Disclosure Number: IPCOM000089221D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Franklin, RE: AUTHOR

Abstract

Digitally generated tones may be different frequencies. Switching from one frequency to another may be accomplished without a change in phase relationship.

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Digital Tone Generation

Digitally generated tones may be different frequencies. Switching from one frequency to another may be accomplished without a change in phase relationship.

Specifically, this is accomplished, as shown in Fig. 1, by segmenting the "on" half-cycles 10 of each tone into an equal plurality of segments. The segments are thus each of a length determined by the frequency of the tone to be generated. Switching from one tone to the other is thus accomplished, as shown in Fig. 2, by terminating (point 12) the generation of one length segment at any point in the half-cycle of the first tone and switching to the other length segment for the remaining number of segments for its half-cycle, thus generating the second tone.

Fig. 3 shows an implementation of this method. Numbers proportional to the intervals for the two tones to be used are stored in registers R1 and R2. The selector 13 determines which of these numbers is to be used by the interval timer
14. If the switching signal is true, R1 is selected. Otherwise, R2 is selected. The output of the selector is used by the interval timer (actually a counter) to generate the appropriate interval. When the interval has been timed out, the interval timer automatically reloads itself with the current output of the selector (thus, the length of the next interval depends on the state of the switching signal at the time the last interval was finished), and also causes the interval timer 15 to advance its count...