Abstract: A transmission apparatus is capable of transmitting a high-speed modem signal. It has at least two types of transmission schemes: one uses a clear channel that can transmit a high-speed modem signal; and the other is a conventional 32-kbit/s or 40-kbit/s ADPCM scheme implemented by a coding section 25. When an ANSam signal detector detects an ANSam signal according to the V.8 protocol from an input signal, a transmission assignment processor instructs a BC (bear channel) bit assignment section to switch the transmission scheme to the higher quality transmission scheme using the clear channel.

Abstract: In establishing an audio one link connection wherein an audio signal is not encoded/decoded in a relay station, loud noises may be produced if the states of two audio tandem relay devices which make a pair during relay are changed from a normal connection state to a relay connection state at different times. In order to solve this problem, comfort noise generators are provided. In detail, when a first pattern signal is detected while a relay call is connected via a relay exchange, switches are switched to be connected at a contact point 1, and a switch is at a contact point 2. Upon detection of a second pattern signal, the switches are connected at the contact points 2, while the switches are connected at the contact points 2. With this arrangement, outputs from the comfort noise generators are selected and outputted during a period from first pattern signal detection to second pattern signal detection, during which the states of the two devices of a pair are different.

Abstract: A reset signal generating part outputs reset signals RV and RD to a signal discriminating part, based on an output from a 2100 Hz detecting part which detects whether or not a tone of 2100 Hz exists in an input signal. When the 2100 Hz tone is detected, the signal discriminating part firstly resets a discrimination state at "speech" and secondly sets the discrimination state at "data" based on the reset signal. Therefore, a signal discrimination apparatus, wherein it is possible to reset the discrimination state at "speech" at the beginning of a facsimile call even when no call control information is received, can be provided.

Abstract: In a voice coding-and-transmission system using a differential coding, a degradation of voice quality caused by a silent period transmission network and an ATM network is prevented without improving a silent-period elimination transmission network and existing transmission networks such as a STM network. In a relay node 104, an encoder 114 codes a voice signal from a decoder 108 again for a transient period immediately after a voice is started, and a transmission node 100 and a reception node 102 are tandem-connected. The encoder 114 and a decoder 122 at a reception node 102 are given respectively same reference values of a differential processing by memories 118, 128 when the voice is started, thereby preventing an abnormal sound generation due to a mismatch of inner statuses thereof when the voice is started. During the transient period, the internal statuses of an encoder 106 at a reception node 100 and the decoder 122 are closed each other.

Abstract: A signal discrimination circuit for discriminating between a voice signal and a voiceband data signal that is transmitted over a telephone network. The signal discrimination circuit includes an electric power judgement unit, a zero-crossing number judgement unit, a sub-band power calculation unit, a tone detection unit, and a discriminated result output unit. The electric power judgement unit determines whether an input signal is a voice signal or a voiceband data signal based on an interblock electric power ratio of the input signal. The zero-crossing number judgement unit determines whether the input signal is a voice signal or a voiceband data signal based on a zero-crossing number of the input signal.

Abstract: An echo canceller is disclosed which is capable of disabling its echo cancelling function when other echo cancellers are connected in tandem in a communications network. A pattern is inserted by extracting bits from a receiving side pulse code modulation (PCM) signal bit stream and replacing them with a predetermined bit-pattern sequence. When the predetermined bit-pattern sequence is detected at a transmission side input PCM signal bit stream, the echo cancelling function is disabled.

Abstract: Improvements in a method of processing wideband audio signals by a sub-band coding system are provided. Linear codes having frequency components in which audio signal power is concentrated are selected from linear codes separated into a plurality of frequency band components and decoded. The presence or absence of sound in the audio signals is detected by referring to the selected linear codes and/or a gain coefficient is determined. Level control of the decoded linear codes is performed by using the thus determined gain coefficient.

Abstract: A speech detector has an intensity detector that indicates whether the intensity of a PCM signal exceeds a first threshold, and a normal-zero-crossing-count detector that indicates whether the zero-crossing count of the PCM signal exceeds a second threshold. The outputs of the intensity detector and normal-zero-crossing-count detector are combined by AND logic to produce the output of the speech detector. The second threshold is set well below the minimum zero-crossing count occurring in normal speech, the function of the normal-zero-crossing-count detector being to disable speech detection during line faults.

Abstract: A digital noise generator for transmitting white noise during a period when a digital telephone speech signal is absent. The digital noise generator includes a pseudo-random bit sequence generator, an amplitude control circuit, and a PCM code-word-generating shift register. A pseudo-random bit sequence is generated by the pseudo-random bit sequence generator, an amplitude code-word is generated by the amplitude control circuit, and pseudo-random noise signal is generated and outputted by the PCM code-word-generating shift register on the basis of the pseudo-random bit sequence and the amplitude code-word.

Abstract: A signalling transmission system is disclosed which consists of a transmitting module including a signalling variation detecting unit and a signalling synthesization unit, and a receiving module including a signalling flag detecting unit and a signalling separation unit. The signalling synthesization unit makes composition signals by inserting signalling signals into voice signals together with a flag when signalling variations are detected by the variation detecting unit. A flag detecting unit detects a flag contained in the composition signals received by the receiving module and instructs the separating unit to separate the signalling signals from the voice signals contained the composition signals when the flag shows that the composition signals include the signalling signals. The signalling signals and the voice signals are therefore output from the receiving module.

Abstract: A plesiochronous matching apparatus has a redundant system including two equipments of the same structure, that is, an on-line equipment (the reference character thereof being accompanied by "a") and a non on-line equipment (the reference character thereof being accompanied by "b"). When the on-line equipment (a) operates normally, the non on-line equipment (b) is made to synchronize with the on-line equipment (a), so that the non on-line equipment (b) is brought into a standby state. Immediately after that, the synchronization connection is dissolved and the non-on-line equipment operates independently of the on-line equipment. The above stated synchronization connection and the dissolution thereof are performed by a synchronization control circuit (57).

Abstract: An incoming signal including the object signal and plurality of noise signals dispersed about the object signal is fully masked with white noise and applied to a phase synchronization loop wide in loop band width and including a local oscillator repeatedly swept by a sweep generator. During the repeated sweep a control signal generator successively decreases the level of the white noise until the oscillator is locked in the phase of the object signal. At that time the signal control generator is operated to suspend the sweeping operation and prevent the white noise from being added to the incoming signal.