The frequency multiplier 20 is embodied by a phase-locked loop including a phase comparator 11 for commanding a plurality of delay elements 130 to 137 that furnish successive phase-shifted signals CL0-CL7 to a logical adder 16 made up of EXCLUSIVE OR gates.

Phase-locked loop and resulting frequency multiplier

A method and system are provided for adaptively reducing noise in frames of digitized audio signals that may include both speech and background noise. Frames of digitized audio signals are processed to determine what attenuation (if any) should be applied to the current frame of digitized audio signals. Initially it is determined whether the current frame of digitized audio signals includes speech information, this determination being based upon an estimate of noise and on a speech threshold value. An attenuation value determined for the previous audio frame is modified based on this determination and applied to the current frame in order to minimize the background noise which thereby improves the quality of received speech. The attenuation applied to the audio frames is modified gradually on a frame-by-frame basis, each sample in a specific frame is attenuated using the value calculated for that frame. The adaptive noise reduction system may be advantageously applied to telecommunication systems in which portable radio transceivers communicate over RF channels because the adaptive noise reduction technique does not significantly increase data processing overhead.

System for adaptively reducing noise in speech signals

To modify the temporal scale of recorded speech, relative stress and relative speaking rate terms are computed for individual sections, or frames, of the speech. These terms are then combined into a single value denoted as audio tension. For a nominal time-scale modification rate, the audio tension is employed to adjust the modification rate of the individual frames of speech in a non-uniform manner, relative to one another. With this approach, compressed speech can be reproduced at a relatively fast rate, while remaining intelligible to the listener.

Non-uniform time scale modification of recorded audio

The speed of an input speech is changed without any change of the pitch of the input speech. Raw data of a speech are stored so that the speed of the speech can be modulated continuously on the basis of the raw data of the speech. In the speech speed conversion method, a speech speed conversion process for the input speech is carried out in a period designated when speech speed conversion is needed, which the speech speed conversion is not carried out in the other period. Further, in the speech speed conversion apparatus having a unit for inputting a speech, a speech speed conversion unit for changing the speed of the input speech, and a unit for supplying the output of the speech speed conversion unit as an output speech to listener's ears, the apparatus further includes a speech speed conversion switch, and a unit for outputting a speech while changing the speech speed of the input speech in a period in which the speech speed conversion switch is turned on, but for outputting a speech without any change of the input speech in the other period in which the speech speed conversion switch is turned off.

Audio signal storing apparatus having a function for converting speech speed

An adaptive high pass filter is used to reduce signal noise such as that occurring on a CATV upstream carrier. A signal detector senses a lowest active frequency on a CATV transmission. A high pass filter is then adjusted to cut off transmissions at frequencies below the lowest active frequency. This reduces ingress noise present in the upstream channel.

Adaptive filter for reducing ingress noise in CATV return signals

An adaptive high pass filter comprises a switched capacitor filter (11) operable as a high pass filter, detecting circuits (14, 15, 16) for detecting low frequency signal components included in an input signal (V i ) and control circuits (17, 18, 19) for controlling the switched capacitor filter (11) responsive to the detecting circuits. In this adaptive high pass filter, a cut-off frequency thereof is controlled responsive to low frequency signal components of the input signal. Therefore, a reproduced voice is not varied dependent upon changes in a quality of voice and surrounding environments. Thus, the reproduced voice is much closer to its original voice.

Adaptive high pass filter having cut-off frequency controllable responsive to input signal and operating method therefor

An audio signal recording and reproducing apparatus digitizes sound into an electric audio signal, data compresses the signal into compressed data to reduce information quantity, records the compressed data into a semiconductor memory, and reproduces an audio signal from the recorded data. The apparatus includes a plurality of input compression and output extension conversion tables which are used for compression conversion of input signal and extension conversion of output signal, respectively. Input compression and output extension conversion table selection counters are count-controlled by difference data representing the change of the audio signal. The apparatus selects one among a plurality of input compression and output extension conversion tables in accordance with count values of the selection counters. The conversion tables are arranged in sequence and contain successively larger ranges of values.

Audio signal recording and reproducing apparatus utilizing digital data compression and extension

An audio signal recording and reproducing apparatus which digitizes sound into an electric audio signal, and data compresses so as to reduce information quantity, and records the same into a semiconductor memory (31) and reproduces an audio signal from the recorded data, includes a plurality of input compression and output extention conversion tables (29, 33) which are used for compression conversion of input signal and extention conversion of output signal, respectively, and input compression and output extention conversion table selection counters (27, 34) which are count-controlled by the difference data representing the change of the audio signal and selects one among a plurality of input compression and output extention conversion tables (29, 33) in accordance with its count value.

An audio signal recording and reproducing apparatus

A privacy communication device uses a control channel (5) in addition to a voice channel (4) in communicating with other privacy communication device. Each privacy communication device employs a ring modulator (8) and a ring democulator (14). A specific modulator carrier frequency to be given to the ring modulator (8) is selected by function of a control signal transmitted on the control channel (5) out of a plurality of modulator carrier frequencies prepared in advance. Likewise, a specific demodulator carrier frequency to be given to the ring democulator (14) is selected by function of a control signal transmitted on the control channel (5) out of a plurality of demodulator carrier frequencies prepared in advance. Hence, when the specific modulator carrier frequency and the specific demodulator carrier frequency are updated at arbitrary intervals, a third person cannot easily identify the varied modulator carrier frequency and demodulator carrier frequency. Thus, secrecy of a voice signal transmitted through the voice channel (4) between the two privacy communication devices is enhanced.

Privacy communication device

PURPOSE: To generate a sinusoidal wave with high accuracy, low distortion and variable frequency through the use of the circuit with a small number of components. CONSTITUTION: A counter 11 counts a clock CLK to obtain count results B0-B4 and they are converted into switching control signals D0-D10 by a control timing generating circuit 12. The timing is adjusted by a synchronizing circuit 13 they become switching control signals Q0-Q10 and they are given to a load resistor circuit 14. The load resistor circuit 14 voltage-divides potential sets VD2, VS2 by the resistance and the voltage divided potential is given sequentially to a low pass filter 15 by the switching control signals Q0-Q10. The low pass filter 15 consists of a switched capacitor in which a frequency fCLK of the clock CLK is used for a transmission zero point. Thus, the sine wave with high accuracy and low distortion is obtained and the sine wave whose frequency is variable is obtained while keeping an excellent high frequency suppression effect. COPYRIGHT: (C)1993,JPO&Japio

Tsutomu Miki

Papers

Adaptive high pass filter having cut-off frequency controllable responsive to input signal and operating method therefor

Audio signal recording and reproducing apparatus utilizing digital data compression and extension

An audio signal recording and reproducing apparatus

Privacy communication device

Sinusoidal wave generating circuit