Nec Corporation

Yasuhiro Wake

Taisuke Sasada

Katsunori Usuki

Signals from microphones are first stored in memory circuits and then supplied to a cross-correlation arithmetic circuit following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences. Signals from the microphones are first stored in memory circuits and then supplied to a cross-correlation arithmetic circuit following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences. A position calculation circuit finds a horizontal direction angle and a vertical direction angle based on these time differences (delay).

Speaker direction detection circuit and speaker direction detection method used in this circuit

In a voice coding section 1, a digital voice signal coded in a voice coder 10, a linear predictive coefficient used as a filter coefficient in a short-term predictive filter 102, a pitch period and a pitch predictive coefficient used, respectively, as a tap coefficient and a filter coefficient in a long-term predictive filter 103, and voice/no-voice status information of an input voice, are multiplexed in a multiplexer 12. Only when the voice/no-voice status information indicate the voice state is a cell assembled and transmitted. In a voice decoding section 2, the received cell is disassembled to provide multiplexed coded data. The voice signal is decoded by a short-term synthesis filter and a long term synthesis filter. The short term synthesis filter uses a linear predictive coefficient as a filter coefficient that is decoded from multiplexed coded data. The long-term synthesis filter uses a pitch period and a pitch predictive coefficient, respectively, as a tap coefficient and a filter coefficient, where the pitch period and pitch predictive coefficient are decoded from the multiplexed coded data. When the cell has been received, the voice signal is output. When the cell has not been received, a noise signal from a noise generator is output. Thus, a voice coding/decoding system can be provided wherein, even upon a change from a silence period to a speech period, the internal state is smoothly transited avoiding the deterioration in voice quality.

Voice coding/decoding system including short and long term predictive

A pause compressing speech coding/decoding apparatus according to the invention can improve the sound quality of decoded speech in terms of sense of hearing, in which the transmission side includes a speech coder, a speech detector, a hangover time controller for adjusting the duration of a speech interval, and a switch for outputting only coded data in a speech interval to a line, and the reception side includes a speech decoder, a noise generator, an amplifier for controlling the output level of the noise generator, a selector for selecting/outputting one of outputs from the speech decoder and the noise generator, a speech/pause data detector for detecting speech/pause data of data from the line, a gain controller for calculating the gain of the amplifier, a level calculator for calculating the signal level of reproduced speech from the speech decoder, and a memory for storing past level values calculated by the level calculator.

Pause compressing speech coding/decoding apparatus

An LD-CELP coder 211 codes an input signal supplied through a telephone line based on the low-delay code-excited linear prediction. A speech detector 212 detects voice/no-voice of the input signal. A FAX terminal input detector 213 detects a FAX signal. A multiplexer 214 multiplexes the coded data and the voice/no-voice data through bit steal of one bit per frame from the code. In a CLAD (cell assembling and disassembling) unit 300, a speech data frame is detected, and also the voice/no-voice information that has been multiplexed in the coded data is detected. If the voice/no-voice information indicates voice, the coded data is converted to cell data to be sent out to a transmission line. Concurrently with the operation of the coder, FAX terminal input data is all converted to cell data and sent out to the transmission line independently of the voice/no-voice information.

ATM transmission system

A speech signal coding system including a speech signal encoder for dividing received speech signals into a plurality of frames each having a predetermined time interval and for converting the speech signals into digital speech parameters. The system includes a multiplexer for multiplexing the output digital data from the speech signal encoder into a predetermined frame format; a control frame generator for generating, in response to an inputted facsimile signal, a control frame having speech data frame configuration for identifying a facsimile signal identification data indicating the input signal as the facsimile signal. A facsimile signal demodulator converts the facsimile signal into digital data and a bit-synchronous multiplexer multiplexes the digital data. An output device outputs the speech data frame of the multiplexer to a digital transmission line and further outputs, when a facsimile signal is input, the control frame and facsimile data multiplexed as the bit synchronous data onto the digital transmission line.

Transmission system for transmitting G3 facsimile signals and compressed

In a multi-pulse excitation encoder, the number of pulses is controlled in accordance with an updated correlation signal compared to a predetermined value.

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Tokyo, Japan

Yasuhiro Wake