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公开(公告)号：AU536715B2
公开(公告)日：1984-05-17
申请号：AU6551580
申请日：1980-12-18
Applicant: IBM
Inventor： FENNEL JOHN W JR , HALLETT ROBERT J , HEAD STANLEY M , MELAS CONSTANTINE M
Abstract: In reconstructing the analog waveform from a syllabically companded delta modulated digital signal transmitted over a TDMA communication channel operating at near its maximum channel capacity, the noise created in a mid-talkspurt freeze-out is greatly reduced by interpolating the amplitude of the waveform during the freeze-out at the receiver as that of the waveform in the previous period. The interpolation occurs for the first 15 msec sampling period following either a freeze-out or a true Voice Activity Compression operation. The interpolation operation is supplied only once so that if two or more consecutive sampling periods occur at the receiver where no channels are received for a particular voice port, background noise is injected into the voice port. This prevents the uncontrolled repetition of the interpolation at the end of a talkspurt.
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公开(公告)号：CA1155978A
公开(公告)日：1983-10-25
申请号：CA365906
申请日：1980-12-02
Applicant: IBM
Inventor： FENNEL JOHN W JR , HALLETT ROBERT J , HEAD STANLEY M , MELAS CONSTANTINE M
Abstract: APPARATUS TO REDUCE THE EFFECT OF A MID-TALKSPURT FREEZE-OUT In reconstructing the analog waveform from a syllabically companded delta modulated digital signal transmitted over a TDMA communication channel operating at near its maximum channel capacity, the noise-created in a midtalkspurt freeze-out is greatly reduced by interpolating the amplitude of the waveform during the freeze-out at the receiver as that of the waveform in the previous period. This makes the quality of voice transmissions in the face of freeze-outs substantially better than prior art techniques which induce background noise during freeze-outs without the necessity of transmitting a voice activity compression (VAC) mask to control the operation of the interpolation apparatus in the receiver. The interpolation occurs for the first 15 msec sampling period following either a freeze-out or a true VAC operation. The interpolation operation is supplied only once so that if two or more consecutive sampling periods occur at the receiver where no channels are received for a particular voice port, the background noise is injected into the voice port. This prevents the uncontrolled repetition of the interpolation at the end of a talkspurt. MA9-78-014
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公开(公告)号：CA1127308A
公开(公告)日：1982-07-06
申请号：CA337634
申请日：1979-10-15
Applicant: IBM
Inventor： YIN HUO-BING , HALLETT ROBERT J
Abstract: ADAPTIVE DELTA MODULATION SYSTEM of the Invention An adaptive delta modulation system is disclosed which features an improved digital compandor which may be used with a digital integrating network. The compandor executes a commanding algorithm having a nonlinear characteristic to provide a rapid increase in step size to follow the fast rise and start or fast decaying end of talkspurts input signals so as to minimize any slope overload distortions and to provide a small increase or decrease in step size during the smooth portion of the talkspurts in input signals to reduce any granular noise effect. The step size generated by the compandor is directly related to the input signal level, providing a maximum companding range in which good signal-to-noise characteristics are preserved for the soft or low voiced speaker as well as for the loud voiced speaker and providing a fast transient response most suitable for telephone applications. The step size logic of the compandor has a built-in minimum step size circuit which insures that a well behaved idle pattern of alternating ones and zeros will appear at the digital output when the input signal is zero, and which provides a mechanism to rapidly build up the step size when an input signal appears. The step sizes can be integrated with an integrating network to reconstruct the input signal. The compandor may be used in conjunction with a digital integrating network which exhibits, for example, a system function, having either a single pole or a zero and a pair of poles which may be real or complex. The filter constants can be chosen to match any input spectrum to obtain optimum performance. A significantly high signalto-noise ratio and a wide companding range have been obtained with the disclosed compandor. By providing storage elements in the compandor and in a digital integrating network and storing the calculated intermediate values, a plurality of input and output analog signals can be time division multiplexed and delta modulated with a single delta modulation system.
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公开(公告)号：CA982697A
公开(公告)日：1976-01-27
申请号：CA160722
申请日：1973-01-08
Applicant: IBM
Inventor： ALVAREZ JOSEPH A , BARNER ROBERT P JR , HALLETT ROBERT J
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