A method of speech signal compression, by variable rate coding of frames of digitized speech samples, comprising the steps of: determining a level of speech activity for a frame of digitized speech samples; selecting an encoding rate from a set of rates based upon said determined level of speech activity within said frame; coding said frame according to a predetermined coding format for said selected rate wherein each rate has a corresponding different coding format; providing for said frame a corresponding output data packet at said selected rate.

Variable rate vocoder

A digital radio receiver is described. The digital receiver of the present invention contemplates a digital radio receiver which operates on a received analog signal which has been converted to a digital form after preselection at the output of the antenna. The digital receiver of the present invention comprises a preselector, a high-speed analog-to-digital (A/D) converter, a digitally implemented intermediate-frequency (IF) selectivity section having an output signal at substantially baseband frequencies, and digital signal processor (DSP) circuit performing demodulation and audio filtering. The radio architecture of the present invention is programmably adaptable to virtually every known modulation scheme and is particularly suitable for implementation on integrated circuits.

Digital radio frequency receiver

The pitch estimation method is improved. Sub-integer resolution pitch values are estimated in making the initial pitch estimate; the sub-integer pitch values are preferably estimated by interpolating intermediate variables between integer values. Pitch regions are used to reduce the amount of computation required in making the initial pitch estimate. Pitch-dependent resolution is used in making the initial pitch estimate, with higher resolution being used for smaller values of pitch. The accuracy of the voiced/unvoiced decision is improved by making the decision dependent on the energy of the current segment relative to the energy of recent prior segments; if the relative energy is low, the current segment favors an unvoiced decision; if high, it favors a voiced decision. Voiced harmonics are generated using a hybrid approach; some voiced harmonics are generated in the time domain, whereas the remaining harmonics are generated in the frequency domain; this preserves much of the computational savings of the frequency domain approach, while at the same time improving speech quality. Voiced harmonics generated in the frequency domain are generated with higher frequency accuracy; the harmonics are frequency scaled, transformed into the time domain with a Discrete Fourier Transform, interpolated and then time scaled.

Voiced/unvoiced estimation of an acoustic signal

An FM broadcasting system is disclosed for transmitting a data signal simultaneously with an auxiliary audio program on the same subcarriers of an FM transmission channel. The main program is transmitted on the FM transmission channel carrier and the auxiliary audio program, which may be background music, is transmitted on the subcarriers in a conventional manner. According to the present invention, the data signal, which is added to the auxiliary audio program, is a binary digital information signal. This binary digital information signal is used to generate a signal which modulates the phase and amplitude of a data reference signal. The resulting phase transition of the modulated data reference signal represents the binary value of the binary digital information signal. The amplitude of the modulated data reference signal then is adjusted in an automatic gain control amplifier relative to the amplitude of a corresponding frequency range of the auxiliary audio program. This amplitude adjusted signal is combined in a linear summing network with the auxiliary audio program and transmitted over the FM transmission channel. The receiver is capable of receiving one or more of the main program, the auxiliary audio program and the data signal.

System for transmitting data simultaneously with audio

A method of designing a high Q inductor for implementation in multiple metalization levels in conventional integrated circuit technology uses a software assisted iterative technique to achieve a design Q factor. The inductor turns utilize the multiple metalization levels to reduce inductor resistance.

Method for designing high-Q inductors in silicon technology without expensive metalization

Speech signal presence is detected in a VAD (Voice Activity Detector) in two steps: (1) Signal energy above a threshold decides presence, below threshold decides ambiguity; (2) ambiguity is resolved by testing the rate of change of spectral parameters.

Voice activity detection process and means for implementing said process

A new adaptive digital tuning filter for tracking a sinusoidal signal within a frequency band is described. The input signal representative of both said sinusoidal signal and noise is fed to a Hilbert transformer which provides the in-phase and quadrature components, x k and x k , respectively, of said sinusoidal signal. These components are applied to the input of a filter having a transfer function K where ##EQU1## WHERE φ = 2πFT, f is the tuned frequency of the filter, T is the signal sampling period and a is a constant close to unity. The output signals y x and y x of the filter are applied to a computing means which provides a frequency control signal e k such that e.sub.k = x.sub.k y.sub.k - y.sub.k x.sub.k The above value of φ is adjusted through a conventional gradient method where φ.sub.k + 1 = φ.sub.k + μe.sub.k and controls are provided to adjust φ in a direction to change e k toward zero. Application of the adaptive tuning filter to cancellation of the main component of phase jitter in a modem is also described.

Self-adaptive digital filter for noise and phase jitter reduction

A method of initializing a filter in an echo canceller as used in a telephone system that includes hybrid transformers for connecting unidirectional lines to bidirectional lines and vice versa. Said method includes the steps of successively transmitting sequences of real and imaginary components of a signal exhibiting an uniform amplitude (i.e. flat) spectrum; receiving and storing sequences of echoes of each of said sequences of components; calculating the fast Fourier transform of complex sequences obtained from the stored sequences of echoes; rotating the terms of the Fourier transform; calculating the inverse transform of the sequence obtained by rotating said terms; and sorting the terms of the inverse transform to derive therefrom the values of the initial coefficients of said filter in said echo canceller.

Method of initializing a filter in an echo canceller and communication system using said method

A data transmitting and receiving system in which data is transmitted by varying the phase and amplitude of a carrier, including a receiver which detects the data in a received signal while reducing the effects of noise components which alter the phase and amplitude of the received signal. An in-phase component and a quadrature component are derived from the received signal and are then rotated an angular amount which is a function of an estimated value of the phase error in the received signal. The rotated components are then compared with two sets of reference coordinates for selecting a pair of reference coordinates which have values closest to the values of the rotated in-phase and quadrature components, respectively. The estimated value of the phase error is derived as a trigonometric function of the rotated components and selected reference coordinates. The selected reference coordinates are indicative of the transmitted data.

System for detecting digital data transmitted by modulating a carrier

A clock setting circuit is provided at a receiving modem for adjusting the phase of a timing signal defining the signal sampling instants. The received signal is filtered in two filters to derive a first signal having a phase φ 1 and a frequency f 1 equal to f c - 1/2T, f c being the carrier frequency and 1/T being the transmission baud rate, and a second signal having a phase φ 2 and a frequency f 2 equal to f c + 1/2T. The first and second derived signals are combined to derive an error signal indicative of the phase difference φ 2 - φ 1 which difference is used for adjusting the phase of a phase locked oscillator which provides the timing signal.

André Desblache

Papers

Voice activity detection process and means for implementing said process

Self-adaptive digital filter for noise and phase jitter reduction

Method of initializing a filter in an echo canceller and communication system using said method

System for detecting digital data transmitted by modulating a carrier

Method and device for synchronizing the receiver clock in a data transmission system