Telephonic communications – Substation or terminal circuitry – Conversion of signal form
Patent
1996-09-25
1999-04-20
Tsang, Fan S.
Telephonic communications
Substation or terminal circuitry
Conversion of signal form
379390, 379391, 379395, 379442, 379447, H04M 900
Patent
active
058964517
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an adaptive telephone interface and is applicable in particular, though not exclusively, to interfacing between telephone terminals and audio input/output devices such as headsets. As used herein a telephone terminal is generally a unit with a numeric or alphanumeric keypad and is commonly connected to a telephone handset containing a microphone and an earphone loudspeaker. Traditionally the user would lift the handset and then type a number into the terminal.
BACKGROUND OF THE INVENTION
It is an increasingly common requirement in communications to have increased flexibility and interchangeability between handsets and/or headsets and the telephone terminals to which they connect, i.e. to be able to connect an earphone/microphone combination or headset unit to a different telephone terminal. To ensure that a signal with a suitable amplitude is transmitted from the headset via the telephone terminal to the destination (which could be another telephone unit), the necessary degree of amplification or attenuation between the telephone terminal and headset needs to be determined. If the transmitted signal has too low an amplitude then it will be too weak to hear easily at the destination. However, if the transmitted signal has too high an amplitude then it will be distorted at the destination. The signal amplitude from the telephone terminal must be optimized so that the signal sent to the headset can be heard clearly at the destination without clipping or distortion of the signal due to overdriving of the terminal. Clipping occurs due to the saturation of the microphone input circuit to the telephone terminal amplifier.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid or minimize one or more of the above disadvantages.
It is also an object of the present invention to provide a telephone interface that gives improved performance over headset and telephone terminal combinations which have no interface and no predetermined gain dedicated for that particular headset/telephone terminal combination.
It is a second objection of the present invention to provide improved performance over headset and telephone terminal units which have non-adaptive interface techniques.
It is a third object of the present invention to provide a device which can adapt a signal for improved transmission without the need for manual gain adjustment.
In general the present invention provides a means for adjusting amplification of a signal sent to a telephone terminal from a headset so as to ensure that a high amplitude signal is sent on from the telephone terminal to the destination without clipping of the signal.
For the purposes of this patent, optimum signal transfer occurs when a high amplitude signal is sent without clipping of the signal. To determine the maximum rms (root mean square) value a signal can have before clipping occurs the crest factor is used. The crest factor is the ratio of the peak value of a signal to the rms (root mean square) value of that signal. For speech, the typical crest factor is approximately five. Using this value of crest factor and the value of the signal amplitude which causes clipping (which is obtained by means of the present invention), the value of rms signal which will just avoid clipping can be determined. Hence the necessary value of gain or amplification to produce that rms signal can be set.
The substance of this invention is the use of a circuit which drives a test signal of varying amplitude into the microphone input of an audio input/output device such as a handset, to a telephone terminal. The sidetone coupling at the telephone terminal results in an attenuated form of the test signal returning, on the output from the telephone terminal that normally drives the speaker output of the audio input/output device. This sidetone is analyzed by a processor to determine at which amplitude of the test signal the sidetone is clipped. Once the test signal amplitude at which clipping begins has been recorded, the gai
REFERENCES:
patent: 4306113 (1981-12-01), Morton
patent: 4782524 (1988-11-01), McQuinn et al.
patent: 4879746 (1989-11-01), Young et al.
patent: 4975949 (1990-12-01), Wimsatt et al.
patent: 5058155 (1991-10-01), Larsen
"Anticlipping" verbessert elektronische Sprechschaltung, pp. 88-93, by Dipl. -Ing. Michael Follner and Dipl. -Ing. Mario Bollinger, Jul. 22, 1988 .
Hsieh Shih-Wen
Jabra Corporation
Tsang Fan S.
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