AU644951B2

AU644951B2 - Call tone analyser

Info

Publication number: AU644951B2
Application number: AU13180/92A
Authority: AU
Inventors: Colin Arthur John Campbell; Kenneth John Nugent
Original assignee: Telecom Technologies Pty Ltd
Current assignee: Telecom Technologies Pty Ltd
Priority date: 1991-04-16
Filing date: 1992-03-25
Publication date: 1993-12-23
Anticipated expiration: 2012-03-25
Also published as: AU1318092A

Description

AUSTRA.IA

Patents Act 1990 P/00/011 28/5/91 Regulation 3.2(2)

ORIGINAL

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S. 90 OS S S. *S Se S 0 Application Number: Lodgqed: Invention Title: PK 5642 16th April 1991 CALL TO~NE ANALYSER The following statement is a full description of this invention, including the best method of performing it known to us *5 5 S eSS S 5* 0 9 S 5e CALL TONE ANALYSER FIELDOF INVENTION The present invention relates to tone detectors for use with telephone network facilities. In particular, the present invention relates to a call tone analyser adapted to detect a call waiting tone in a single line telephone system.

BACKGROUND ART: In a network of single line telephone users, external messages can be presented to a telephone user speaking on a telephone, without the need for an additional communication channel. An example of this is a call waiting tone which indicates to a user that a second call has been made to that telephone when the user is already engaged on a telephone call. This tone is preseied to the telephone handset earpiece and the user may then elect to terminate or suspend t;e first call and accept the incoming call.

Voice signals by their very nature have frequency components at various levels and frequencies used in a telephone voice communication band. Voice frequencies typically and randomly vary over the range of 300 to 3500 Hz. A call waiting tone is superimposed over voice signals to avoid the need for additional communications channels.

In Australia, a call waiting tone service is provided as an optional service for subscribers. The call waiting tone is generated at the telephone exchange when a new d* call is waiting and consists of a distinct pitch, level, cadence and periodicity. The call waiting tone (used currently by Telecom Australia) has a frequency of 425 Hz, which Is also a frequency at which speech occurs. Accordingly, detection of a call tone signal in the presence of voice signals is difficult, as a voice signal at 425 Hz may trigger the 25 call tone detector of the prior art arrangements.

The call waiting tone is, for example in Australia, typically two 200 millisecond bursts of 425 Hz tone, with a 200 millisecond pause between bursts.

This "burst, pause, burst" pattern may then be repeated every 5 seconds, although repetition of the pattern may not be required where the call waiLt!ng tone can be 30 determined relatively accurately the first time. This pattern usually continues for seconds, o' until the second waiting call is answered.

The presence of a tone at a fixed level for a short duration can sometimes be imitated by voice signals, or it may sometimes be masked by voice signals.

U.S. 3,103,558 discloses one form of call tone detector, in which voice and call waiting tone signals are separated. During use of the telephone, when a voice I I 2 signal is present, a signal suppressor greatly distorts the voice signal by greatly amplifying only the voice signal. The signal suppressor does not amplify the call waiting tone and thus the greatly amplified voice signals swamp the call waiting tone signal and the tone signal has little practical effect. When no voice signal is present, the control signals are not swamped.

OBJECT OF INVENTION: An object of the present invention is to provide a call tone analyser which reliably detects a call waiting tone.

A further object of the present invention is to provide a telephone 1 0 incorporating a call tone analyser of the present invention which provides additional stimulus to the user to visually indicate a waiting second call; associating this indication with a dedicated key which the user may merely press to complete the connection.

SUMMARY OF INVENTION: The present invention takes advantage of a pause or low level in the voice ;signals that will inevitably occur during a conversation to determine the presence of a call waiting tone. The purpose of the inventon. is to detect the call waiting tone as accurately as possible. Tlie present invention seek, to identify an analogue signal amongst other analogue signals at equal or higher levels. The present invention 20 operates in parallel with the normal operation of the telephone speech path.

:The call waiting tone may have any frequency or periodicity, dependent on the type of telephone exchange used in a country, and the call tone analyser of the present invention may be appropriately configured with regard to frequency or periodicity to detect the presence of the call waiting tone. Upon detection of a call waiting tone, 25 additional stimulus may be given to the user to alert the user to the presence of the call waiting tone.

In one form, the present invention provides a device adapted to signal the presence of a call waiting tone when a communication channel is in use, said device comprising a communication channel signal analyser for providing as an output a detection signal indicative of the presence of a call waiting tone in the absence of a voice signal on said communication channel.

The detection signal analyser may also include logic means to determine whether said detection signal has a periodicity within a predetermined time range, where the call tone is repeated.

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0 5 St 0 k IO* S is S 0* *5 The present invention also provides a call tone analyser means for a communic lon channel, said analyser means being adapted to determine the presence of a call waiting tone and to indicate the presence of a waiting call whilst the communication channel is in use, said analyser means comprising in combination, a frequency detector adapted to detect the presence of a signal at a predetermined frequency, said predetermined frequency corresponding to the frequency of a call waiting tone, a voice signal detector adapted to provide an indication of the presence or absence of voice signals in the communication channel, and 1 0 logic means for providing as an output, an indication of the presence of the call waiting tone In the absence of the voice signals.

In another form, the present invention provides, in a telephone, a call tone analyser means, wherein, in response to an output of the analyser means, there is provided an addltlo ;al stimulus to the user to indicate the presence of a call waiting tone. The additional stimulus may be a visual indication to the user that there is a call waiting tone.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, wherein Figure 1 shows a typical exchange/telephone interconnection for use with the 20 present invention; and Figure 2 shows one form of the call tone analyser of the present Invention implemented in a telephone.

In its preferred embodiment, the call tone analyse, of the present invention takes advantages of pauses and low levels in a speech pattern to uncover the presence of a call waiting tone. A detailed timing analysis of 200 millisecond bursts of a detected call tone is undertaken to enable relatively accurate and reliable detection.

The call waiting tone may be altered in duration and periodicity and this is dependent upon the type of tone provided on the telecommunication neltork. The analyser would therefore need to be modified or altered to detect the altered tone. For example, the 30 tone may have a 100 millisecond burst, with or without the 5 second periodicity.

The call waiting tone detection hardware of the present invention operates in parallel with the normal operation of the telephone speech path. Figure 2 illustrates the location of the tone detection circuitry. In the preferred embodiment the point of extraction of the signal is at the receiver output from the telephone voice circuit.

Only signals from the telephone exchange are analysed for tone content.

There are two functions to the hardware a) Detection of the signalling tone (Tone Detect), in which to detect the presence of the burst of 425 Hz, a single chip, phase lock loop (PLL) is used. This PLL provides an output indicative of a signal being detected at 425 Hz; and b) Detecting pauses in, and low levels of, voice (Voice Detect), in which a band reject filter (at the call waiting tone frequency) in combination with rectification, RC timing, and logic level conversion is used to produce a logic signal which indicates the presence of any frequency, above a minimum level, other than that of the call waiting tone frequency.

1 0 The output of the voice detector is logically ANDed with the tone detector output. This leads to the logical output of "there is a tone when there is no voice".

Unfortunately this logic does not cover the case of the voice mimicking the tone bursts which may occur durinL certain speech patterns. Thus this logical output is analysed for the 200 millisecond, BURST, PAUSE, BURST, timing.

1 5 The timing analysis is provided by logic formed from available digital components. The task is to determine if there is a valid 200 millisecond, BURST, *PAUSE, BURST of tone. There are several challenges here Firstly, the PLL does not respond with exactly the same turn on and turn off timings as the line length and voice patterns vary. Thus there needs to be a wide 20 acceptance criteria for the 200 millisecond tone. Similarly the 200 millisecond pause followed by the second burst must be timed, and a determination of the 200, 200, 200 millisecond cadence of the burst confirmed.

Secondly, because the signalling 200 millisecond tone or pause may be instantaneously interrupted by a voice signal, the analyser also incorporates error 25 bridging features. If the interruptions are less than a predetermined length then the interruptions are Ignored.

Thirdly, once the first call waiting tone is detected, the analyser must next determine if the waiting tone pattern is repeated in accordance with the call tone criteria generated at the telephone exchange. Obvioosly, where no repetition of 30 waiting tone pattern is provided, the call tone analyser is appropriately configured.

The present invention can be modified to analyse a call tone of different time criteria, as would be appreciated by those skilled in the art.

Once all of the above criteria have been met the analyser of the present Invention then alerts the user of the telephone. This may be done, for example, by 3 5 illuminating a LED on the telephone or sounding ar; alarm or by other suitable means.

I j I It has been found of advantage to utilise a visual indicator, such as an LED in the telephone, in addition to an audible toning in the earpiece. In this way, a user of the telephone is provided with a number of stimuli to indicate the presence of a waiting call. Additional stimuli serve to make the user more aware of the waiting call as, if merely an audible indication is given to the user, it may not be noticed during or may be masked by normal speech occurring on the communication channel.

Once the user is alerted then he may choose to press the appropriate buttons on the telephone to place the current conversation temporarily on hold, and then proceed to answer the waiting call.

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Claims

1. A call tone analyser for a communication channel, said analyser being adapted to determine the presence of a call waiting tone having a predetermined pattern whilst the communication channel is in use, said analyser comprising in combination, a frequency detector adapted to detect the presence of a signal at a predetermined frequency, said predetermined frequency corresponding to the frequency of a call waiting tone, a voice signal detector adapted to provide an indication of the presence or absence of voice signals in the communication channel, and logic means for providing as an output, an indication of the presence of the call waiting tone in the absence of the voice signals.

2. A call analyser as claimed in Claim 1, wherein the call waiting tone has a predetermined burst, pause, burst pattern. off*

3. A call analyser as claimed in Claim 1, wherein each burst of the pattern is i ao substantially 200 milliseconds and the pause is also substantially 200 milliseconds in ~duration.

4. A call analyser as claimed in Claim 1, 2 or 3, wherein the communication channel is a single line.

A call analyser as claimed in Claim 1 or 4, wherein the call tone is an analogue t ilgnal. 0

6. A call analyser as claimed In any one of Claims 1 to 5, further comprising 0* Si 6 Indicator means adapted to provide at least one stimulus to a user of the communication channel upon detection of a call waiting tone.

7. A call aralyser as claimed in Claim 6, wherein the indicator means includes a visual indication provided In a telephone.

8 A telephone Including a call tone analyser as claimed in any one of the preceding claims. I 7

9. A device adapted to signal the presence of a call waiting tone when a communication channel is in use, said device comprising a communication channel signal analyser for providing as an output a detection signal indicative of the presence of a call waiting tone in the absence of a voice signal on said communication channel, and a detection signal analyser having logic means to determine whether said detection signal has a periodicity within a predetermined time range.

A device as claimed in Claim 9, wherein the communication channel signal analyser includes a band pass filter means for detecting the absence of a voice signal on said channel, a notch filter means detecting the presence of a tone at the frequency of a call waiting tone and logic means adapted to AND the output of the band pass filter means and notch filter means.

11. An analyser as claimed in Claim substantially as herein described with reference to the accompanying drawings. 00** SDATED THIS 17TH DAY OF MARCH, 1992 TELECOM TECHNOLOGIES PTY. LTD. WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN, VICTORIA 3122 AUSTRALIA LD:RCTS:JC 0 DOC 13 AUOOOPK5642.WPC •0 411 0.0,0 0I 00 ABSTRACT The present invention relates to a call tone analyser for a communication channel, said analyser being adapted to determine the presence of a call waiting tone having a predetermined pattern whilst the communication channel is in use, said analyser comprising In combination, a frequency detector adapted to detect the presence of a signal at a A* predetermined frequency, said predetermined frequency corresponding to the frequency of a call waiting tone, a voice signal detector adapted to provide an indication of the presence or absence of voice signals in the communication channel, and logic means for providing as an output, an indication of the presence of the call waiting tone In the absence of the voice signals. Ur S* h 9 0