Nec Corporation

Nippon Electric Co., Ltd.

Tadaharu Kato

Takao Nishitani

Ichiro Kuroda

Masahiko Mori

For transmission and reception of an ADPCM stream in which each of signal components is represented by a predetermined number of bits, an ADPCM transcoder comprises a bit number determining device (43) for producing a bit number signal representative of first and second bit numbers one at a time to make the ADPCM stream carry a voice component with the first bit number and a data component with the second bit number as two of the signal components. The first bit number is less than the second bit number. Preferably, a sum of the first and the second bit numbers is not greater than twice the predetermined number to make one of the two signal components comprise the voice component and a less significant part of the data component. The first and the second bit numbers are calculated from a voice and a data optimum scale factor which can be calculated by a method similar to adaptive prediction. The bit number signal need not be carried by the ADPCM stream. Alternatively, the transcoder may multiplex the bit number signal in the ADPCM stream for transmission and demultiplex the bit number signal from the ADPCM stream received to determine the first and the second bit numbers for use in an ADPCM decoder included therein.

ADPCM transcoder wherein different bit numbers are used in code

Apparatus for use in receiving input signals through order wires; at least one of the input signals is a specific signal including an input control signal indicative of supply of the specific signal to either a telephone set (6) or a facsimile set (15). A processing circuit processes (2) the input signals into an input single signal; an input detecting circuit (3) detects the input control signal in the input single signal; a judging circuit (14) judges whether the input control signal indicates supply of the input single signal to the telephone set, or to the facsimile set and produces an input connection signal; and a connection unit (20) connects the processing circuit to the telephone set and to the facsimile set when the input connection signal indicates the telephone set and the facsimile set, respectively. It is also possible to use the apparatus to transmit output signals produced by the telephone set and the facsimile set through the order wires.

Apparatus for communication by telephone set and facsimile set through

Speech presence is detected by first comparing input signal absolute value versus a first threshold which is proportional to input signal RMS noise power, accumulating the first comparison output signal, then comparing the accumulated signal versus a second threshold signal which is proportional to a hangover time signal. The first and second threshold signals are used to form up to six threshold values.

Speech signal detector having adaptive threshold values

In an APDCM decoding circuit, an adaptive inverse quantizer which forms a quantized coded signal, produces a residual signal and upper and lower limits thereof. An adaptive prediction circuit uses the residual signal to predict a quantization, which is added to the other signals. The added residual is converted into a nonlinear encoded PCM for output. However the output is PCM linearized and compared to the added upper and lower limits to determine if the output should be incremented or decremented.

Adaptive differential pulse code modulation decoding circuit

A digital pushbutton (PB) signalling receiver having reduced sampling frequency for reducing the operations required by digital filters. The PB receiver is responsive to an in-band audio signal digitized at a conventional sampling frequency (e.g., 8 KHz) and detects two PB frequencies, one from a lower group and one from a higher group of frequencies. The input signal is successively digitally filtered and sampled, with each sampling frequency being reduced by 1/2 from the preceeding sampling frequency. This results in two digitized outputs, both of which are much lower sampled digitized signals than the input, and each of which contains information corresponding to said lower and higher groups of frequencies, respectively. The two outputs are then applied to two banks of frequency detectors, comprising digital band-pass filters and energy calculating circuits, for providing an indication of the presence of the lower and higher group of frequencies in the original input signal.

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Tokyo, Japan

Tadaharu Kato