Browse Prior Art Database

Digital Generation of Audible Progress and Multifrequency Tones Using PCM

IP.com Disclosure Number: IPCOM000084642D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

DiNicola, PD: AUTHOR [+3]

Abstract

In telecommunications switching systems, mutually distinctive audible tones (e.g., dial tone, ringback, busy) are employed to keep the user informed of the progress of his call. These tones are derived from four basic frequencies (350, 440, 480 and 620 Hz), either alone or in pairs. Sixteen distinct push button dialing or multifrequency (MF) tones are used for the transmission of sequences of digits from push button telephones, in order to establish connections. Each MF tone consists of a specific combination of two basic frequencies out of a group of eight (697, 770, 852, 941, 1209, 1336, 1477 and 1633 Hz).

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Digital Generation of Audible Progress and Multifrequency Tones Using PCM

In telecommunications switching systems, mutually distinctive audible tones (e.g., dial tone, ringback, busy) are employed to keep the user informed of the progress of his call. These tones are derived from four basic frequencies (350, 440, 480 and 620 Hz), either alone or in pairs. Sixteen distinct push button dialing or multifrequency (MF) tones are used for the transmission of sequences of digits from push button telephones, in order to establish connections. Each MF tone consists of a specific combination of two basic frequencies out of a group of eight (697, 770, 852, 941, 1209, 1336, 1477 and 1633 Hz).

In switching systems which employ time division multiplexing (TDM) of coded digital signals, it is convenient to switch the signals representing the progress and MF tones in the same manner which is applied to voice signals. Generation of these tones directly on pulse code modulated. (PCM) form can be accomplished economically, by personalizing a read-only storage (ROS) with the bit patterns representing the twelve basic, single-frequency sinusoids.

To generate each tone sample, bit patterns for the two sinusoids required for the generation of the specific tone are gated out of ROS into the ROS output registers (ROSOR) and a binary addition of the two is performed, and the result is stored in a tone data register (TDR). In the case of the single-frequency tone, the basic sinusoid may simply be added to itself.

The addition of the two sinusoids having equivalent power levels causes an increase in power of 3 dbm from the stored waveform to the resultant tone. However, the adder can include a shift right-left shifter for adjusting output digital value to the desired level in 3 dbm (factor of 2) steps.

The system clock is used to increment a slot counter whi...