Abstract: A method of removing noise and interference from a signal by receiving the signal, calculating a joint time-frequency domain of the signal, estimating instantaneous frequencies of the joint time-frequency domain, modifying each estimated instantaneous frequency, if necessary, to correspond to a frequency of the joint time-frequency domain to which it most closely compares, redistributing the elements within the joint time-frequency domain according to the estimated instantaneous frequencies as modified, computing a magnitude for each element in the joint time-frequency domain as redistributed, plotting the results as the time-frequency representation of the signal, identifying in the plot any noise and interference components in the received signal, eliminating from the redistributed joint time-frequency domain elements that correspond to noise and interference, and recovering a signal devoid of noise and interference from the modified redistributed joint time-frequency domain.

Abstract: A speech synthesis apparatus, which can embed unchangeable additional information into synthesized speech without causing a deterioration of speech quality and restriction by bands, includes a language processing unit which generates synthesized speech generation information necessary for generating synthesized speech in accordance with a language string, a prosody generating unit which generates prosody information of speech based on the synthesized speech generation information, and a waveform generating unit which synthesizes speech based on the prosody information, in which the prosody generating unit embed code information as watermark information in the prosody information of a segment having a predetermined time duration within a phoneme length including a phoneme boundary.

Abstract: A stereo receiver of a simple structure is disclosed capable of continuously controlling the degree of separation of left and right voice signals in accordance with the level of electric field strength. The stereo receiver comprises electric field strength detecting means 9 for detecting the electric field strength of a received signal, and a stereo demodulation circuit 5 for outputting original voice signals of left and right channels. A blend circuit 6 is provided for blending the original voice signals with each other to output blended voice signals of the left and right channels. The degree of blending between the original voice signals is continuously changed correspondingly to the electric field strength. As a result, the S/N, which may deteriorate when the electric field strength is low, can be improved with a simple structure.

Abstract: A method and device for reducing error components of a multi-channel modulator. The method comprises the steps of inverting substantially half of the channels of a modulator, and reducing error components between said inverted channels and said non inverted channels by inductive and/or capacitive summing. The method is especially suitable for synchronized pulses and similar signals to be modulated.

Abstract: A compander for noise reduction of a FM signal is described, wherein a group delay (?) linked to the generation of the compressor gain (cc(t)) is equalised during generation of the multiplex signal (m(t)), and a group delay (?) linked to the generation of the expander gain (ce(t)) is equalised during generation of the sum signal (us(t)) and the expanded difference signal (ue(t)). Alternatively or additionally the compressor gain and/or the expander gain is controlled by an auxiliary signal on the basis of a combination of sum signal and difference signal of the FM signal. Such companders avoid overmodulation in the transmitter.

Abstract: Predistortion effective for a power amplifier with the memory effect is provided. An A/D converter digitizes a signal voltage value after quadrature modulation, and the result is supplied to a subtractor. A lookup table outputs voltage value data in accordance with an output of the subtractor. The output of the lookup table is used as address data for accessing respective lookup tables. The lookup tables output an accumulation adding value derived from multiplying, by impulse responses, the signal voltage value after quadrature modulation and supplies it to the subtractor. The voltage value data outputted from the lookup table is converted by a D/A converter to output it as a predistortion signal for amplitude component for the power amplifier.

Abstract: A FM broadcast compander system is combined with a conventional denoising system suited for FM receiver, wherein a noise indicator is determined by a subtraction of the conventionally transmitted difference signal Ud(z) from the additionally transmitted difference signal (Uc(z)) which is additionally transmitted according to the companding system. This system gives a noise reduction of 20 dB in a stereo FM broadcast receiver.

Abstract: An I/Q modulator used for processing an I/Q signal to obtain a predistorted output signal. The I/Q signal has an I component and a Q component, and comprises a predistorter for predistorting, with a predistortion signal, a carrier signal, which comprises a first subcomponent and a second subcomponent that is substantially orthogonal to the first subcomponent, to obtain first and second predistorted subcomponents of the carrier signal. The predistortion signal depends on the I and Q components. A first multiplier multiples the I component by the first predistorted subcomponent to obtain a multiplied I component. A second multiplier multiples the Q component by the second predistorted subcomponent to obtain a multiplied Q component. An adder adds the multiplied I component and the negative multiplied Q component to obtain the predistorted output signal. Thus, a simplification of the I/Q modulator and a reduction in the number of necessary multipliers is achieved.

Abstract: A method to denoise a stereo signal which comprises a stereo sum signal (Us(z)) and a stereo difference signal (Ud(z)), wherein a stereo to mono blending on basis of an attenuation of the stereo difference signal (Ud(z)) is performed, determines an attenuation of the stereo difference signal (Ud(z)) under consideration of the difference signal amplitude. Therefore, a stereo signal noise reducer which performs a stereo to mono blending on basis of an attenuation of the stereo difference signal, comprises an attenuation factor determination unit which determines an attenuation factor (Hatt) under consideration of the difference signal amplitude.

Abstract: For the purpose of largely suppressing the noise pulses caused in a stereo radio receiver in the reception signal, particularly by the ignition system of a motor vehicle, a digital field strength signal representing the analog field strength signal is produced for example by digitizing the analog field strength signal. The scanning values of the digital audio signal, for example of the (L+R) signal, are produced by interpolation for at least as long as the digital field strength signal is outside a presettable tolerance range.

Abstract: A method to denoise a stereo signal comprising a stereo sum signal and a stereo difference signal, performs a frequency selective stereo to mono blending based on the masking effect of the human auditory system. Therefore, a stereo signal noise reducer, comprising a first filter bank (1) to split the stereo difference signal (1?r) into a plurality of subbands, respective first multipliers (20, . . . , 2N) to weight each of the subbands of the stereo difference signal with a respective corresponding control signal (C0, . . . , CN), and a first adder (3) to sum all weighted subbands of the stereo difference signal (1?r) to build a frequency selective weighted stereo difference signal (diff), within which a number and width of the subbands obtained via the first filter bank (1) are choosen according to the properties of the human auditory system, further comprises a weighting factor determination unit which determines a respective control signal (C0, . . .

Abstract: An AM neighboring interference removing method and circuit is provided which can select only a desired AM modulation wave even if an interference AM modulation wave is partially superposed upon the desired AM modulation wave. An AM modulation wave desired to be received is multiplied at multipliers by local oscillation signals having frequencies 3fc/2 and fc/2 where fc is the carrier frequency of a neighboring interference AM modulation wave. High frequency components contained in the outputs of the multipliers are removed by low-pass filters. Of the outputs of the low-pass filters, the carrier frequency of the neighboring interference wave is fc/2 and the AM carrier frequencies of the AM stereo modulation wave are (fc/2+f?) and (fc/2?f?), where f? is a difference frequency between the AM carrier frequency of the AM stereo modulation wave and the carrier frequency of the neighboring interference wave.

Abstract: Distortion discrimination circuitry for digital radio receivers and corresponding methods are disclosed that accurately and efficiently discriminate distortion events, including impulse noise and multipath distortion events, to improve the quality of audio output signals. The distortion discrimination circuitry monitors and analyzes the demodulator output to determine when a distortion event has occurred and provides an appropriate indication signal for use by other circuitry within the radio receiver. More particularly, the distortion discrimination circuitry includes impulse noise circuitry that looks for high frequency noise in both the magnitude and multiplexed outputs of the demodulator to determine the occurrence of impulse noise distortion events.

Abstract: An improved noise reduction system (20) is provided for a radio frequency audio processor having one or more weak signal processing components for generating one or more corresponding control values (36a, 36b) for controlling characteristics of the audio output from the processor, and a blanking pulse generation component (10) for generating a blanking pulse signal (18) in relation to an impulse noise signal imposed on the radio frequency signal. The improvement (20) can include at least one detector (30a, 30b) for determining a state value of the blanking pulse signal, such as the pulse density or frequency. At least one alignment function module (32a, 32b) is provided that is operable on the state value to generate at least one corrected control value corresponding to one of the weak signal processing components.

Abstract: Audio signals are reproduced with consistent perception of total harmonic distortion even with varying spectral content of a particular audio signal without separately limiting different frequency bands within the audio signal. A distortion threshold representative of an amount of distortion to be allowed to be introduced by a power amplifier is determined in response to a frequency content of the audio signal. A distortion trigger compares a measured average distortion signal and the distortion threshold and reduces the controllable gain of the amplifier if the average distortion signal exceeds the distortion threshold.

Abstract: A method and apparatus for minimizing multipath interference for commercial FM signals which use SCA secondary signals in QAM format that includes tracking the time series of phase measurements of a received stereo pilot signal for determining the proper phase reference for demodulation of QAM signals at the center of the time series. Phase measurements of the pilot signal are tracked over a predetermined tracking period. The phase measurement is used to support demodulation of the QAM signal. The SCA secondary signals in QAM format transmitted on commercial FM have minimal multipath interference and Doppler interference by movement of transmitter and receiver (vehicular).

Abstract: An audio signal noise reduction system comprises a noise detecting circuit 11 for detecting a noise from an audio signal and outputting a detection signal indicating a start time and an end time of a noise period of the noise, an LPF 12 for extracting a low frequency component of the audio signal, an HPF 14 for extracting intermediate and high frequency components of the audio signal, a polynomial interpolation circuit 13 for polynomial-interpolating the noise period of the low frequency component being extracted, a mute circuit 15 for muting an output level of the noise period of the intermediate and high frequency components being extracted, and a signal synthesizing circuit 16 for synthesizing the low frequency component whose noise period is polynomial-interpolated and the intermediate and high frequency components the level of whose noise period is suppressed to thus output the audio signal.

Abstract: The noise in a frequency demodulated audio signal is detected on basis of the characteristics of the stereo-multiplex signal to obtain a very reliable information that can be used for the sliding stereo-mono transition, noise blanking and a de-noising of the stereo-difference signal. A noise signal (vd,l(t)−vd,u(t) or vd,u(t)−vd,l(t)) is calculated by subtracting one sideband of the stereo-difference signal from the other sideband of the stereo-difference signal and as a direct measure for the quality of the signal generating the variance (&sgr;2vd) of the noise signal by squaring and thereafter averaging the noise signal.

Abstract: A stereo radio receiver has a channel separation stage for setting an optimal channel separation of the left audio channel from the right audio channel, even under sufficient receiving field strength following a time of multipath reception for the duration of the operating time of a timing element, to a reduced (i.e., lesser degree of) channel separation.

Abstract: Clicks in voice and music signals are removed by detecting and interpolating the click. The use of a permanently set threshold value above the peak value of the audio signal is known for detecting the clicks, and interpolation carried out on the basis of the sample values before and after a click is known for filling them in. Disadvantages of these methods are, on the one hand, that many clicks do not have a larger amplitude than the peak signal and therefore remain undetected, and, on the other hand, interpolation is a highly complex procedure and is limited to a maximum click density. The invention provides for an error signal (en) to be determined by adaptive filtering (AF). A sample value is designated as distorted in the input signal (xn) if the absolute instantaneous value in the error signal (en) exceeds a dynamically adapted threshold value.

Abstract: A method for generating a frequency-modulated signal with high receivability quality, comprising the steps of: before sending an input modulating signal to a modulator, modifying the input modulating signal so as to compensate for distortions which will be introduced in the modulated signal receiving section.

Abstract: A method to denoise a stereo signal which comprises a stereo sum signal (Us(z)) and a stereo difference signal (Ud(z)), wherein a stereo to mono blending on basis of an attenuation of the stereo difference signal (Ud(z)) is performed, determines an attenuation of the stereo difference signal (Ud(z)) under consideration of the difference signal amplitude. Therefore, a stereo signal noise reducer which performs a stereo to mono blending on basis of an attenuation of the stereo difference signal, comprises an attenuation factor determination unit which determines an attenuation factor (Hatt) under consideration of the difference signal amplitude.

Abstract: A method to denoise a stereo signal comprising a stereo sum signal and a stereo difference signal, performs a frequency selective stereo to mono blending based on the masking effect of the human auditory system. Therefore, a stereo signal noise reducer, comprising a first filter bank (1) to split the stereo difference signal (1−r) into a plurality of subbands, respective first multipliers (20, . . . , 2N) to weight each of the subbands of the stereo difference signal with a respective corresponding control signal (C0, . . . , CN), and a first adder (3) to sum all weighted subbands of the stereo difference signal (1−r) to build a frequency selective weighted stereo difference signal (diff), within which a number and width of the subbands obtained via the first filter bank (1) are choosen according to the properties of the human auditory system, further comprises a weighting factor determination unit which determines a respective control signal (C0, . . .

Abstract: A noise suppressor has signal detecting device 1 for detecting signals A and B on signal lines, sum signal generating device 21 for summing the detected signals, difference signal generating device 22 for differencing the detected signals, noise canceling device 3 for suppressing or removing noise components in a difference signal generated by the difference signal generating device and signal separating device 4 for separating the signal to those corresponding to the signal lines, according to the difference signal with the noise components suppressed or removed and the sum signals.

Abstract: The apparatus for encoding a plurality of digital information signals, having at least a first input unit for receiving a first digital information signal and a second input unit for receiving a second digital information signal. A signal combination unit combines the first and second digital information signal to generate a first combination signal. First and second data compression units compress the first and second digital information signal so as to obtain first and second data reduced digital information signals. First, second, and third masked threshold determining units determine first, second and third masked thresholds respectively from the first, second digital information signals and the combination signal respectively. A selection unit selects one masked threshold from the first and third masked threshold so as to obtain a first selected masked threshold. Preferably, the first selected masked threshold is the smallest of the first and third masked thresholds.

Abstract: It is a primary object of the invention to provide a noise suppressing device in which the function to suppress or remove the noise is more improved than the conventional device. The invention comprises a tuner section which detects the radio wave and converts it to the electric signal, an antenna connected to the tuner section, a field/disturbance information-detecting section for detecting the carrier level and the like of the input signal based on the signal from inside of the tuner section, a modulation information-detecting section for detecting the modulation degree and the like based on the signal from inside of the tuner section, a noise suppression control section which suppresses or removes the noise from the noise-containing signal input from the tuner section, a noise cancel section, and a noise data-generating section; and the noise-removed signal is output to an amplifier and amplified and sent to a speaker.

Abstract: An FM radio receiver, particularly for mobile receivers, reduces the effects of multipath distortion. It selects either an adaptive process (constant modulus algorithm or CMA) or a antenna diversity process depending on the circumstances of the instantaneous reception. The receiver reduces both the decline of the level of received signals with the diversity process and waveform distortion with the CMA process.

Abstract: A system and method are provided for reducing perceived distortion in an output audio signal derived from an amplitude modulated compatible digital broadcast signal having a monophonic portion and a stereo portion. The stereo portion of this signal is demodulated to produce a demodulated stereo signal and the monophonic portion of the signal is demodulated to produce a demodulated monophonic signal. The noise in the demodulated stereo signal is measured and an estimate of the signal-to-noise ratio is derived. This estimated signal-to-noise ratio is compared with a threshold level which is set at the minimum acceptable signal quality for the stereo signal. Based upon the estimated signal-to-noise ratio, a switch directs either the monophonic derived audio output or the stereo derived audio output as the system output signal.

Abstract: A multipath interference reduction system and method for smoothly reducing noise associated with FM stereo signal reception with an adjustable blend. The system includes a peak detector for detecting noise present in the received signal. When the detected noise exceeds a first threshold limit, stereo separation reduction is provided. The amount of stereo separation reduction may be adjusted so as to provide a greater reduction at higher noise frequencies than at lower noise frequencies to enhance the audio sound. When the determined noise exceeds a second higher threshold limit, stereo separation is further reduced to provide primarily monoaural reception.

Abstract: In a circuit for mobile radio receivers with a device for setting the stereo reproduction portion relative to the mono reproduction portion as a function of changes in the reception field strength, the setting time for the transition from stereo to mono reproduction and vice-versa depends on the reproduction volume and/or dynamic response of the radio signal.

Abstract: In a broadcast receiver, a dynamic compression of the signal is switched on or off in dependence on whether such a compression has been carried out at the transmitting end. An identification bit is transmitted for identifying this compression at the transmitter end. The object is to create a broadcast receiver which effects automatic switching-on or switching-off of an amplitude compression but manages without a transmitted identification bit. The received audio signal is applied to a signal analysing circuit which determines the scale factors of the signal and generates switching voltages dependent on the scale factors. The present invention has particular applicability for broadcast receivers in a motor vehicle or with subsequent signal recording.

Abstract: In a circuit for deriving at least one quality signal that is dependent on the quality of a received signal, where the received signal is demodulated, a first auxiliary signal which is dependent on the field strength, and a second or further auxiliary signal, are derived from the demodulated signal. The auxiliary signal and the second or further auxiliary signal are combined to derive the quality signal.

Abstract: A control for an FM receiver reduces multipath distortion by reducing stereo separation and high frequency response in the demultiplexed signal. The receiver includes an FM detector including a noise detector as well as the signal strength meter for introducing control signals to a separation control and a frequency response control. Unlike the direct input from a noise detector output to the separation and frequency response controls in the prior art, the noise detector output is input through a noise detection manager that generates responses to at least one, and preferably two thresholds of noise detector output. In the preferred embodiment, a stereo separation manager responds to a first threshold of noise and a frequency response manager responds to the second threshold. The frequency response control reduces the high frequency output at the stereo decoder or the audio processor.

Abstract: A radio receiver is provided having digital signal processing, a first and a second auxiliary signal derived from a received stereo multiplex signal, the first auxiliary signal being dependent upon the existence of signal components, whose frequency lies above the fundamental frequency range of the stereo multiplex signal, and the second auxiliary signal being dependent upon the symmetry of the sidebands of the stereo subcarrier. The first and the second auxiliary signal are combined to form an interference signal indicating the existence of interference. At least one control signal is derived from the interference signal to influence the audio signals acquired by decoding the stereo multiplex signal.

Abstract: The circuit arrangement includes a first low-pass filter (2) for filtering an input signal (H3) proportional to the strength of a received radio signal; a second low-pass filter (3) for filtering the input signal (H3); a first weighting circuit (7) for weighting the first low-pass filter output signal with first coefficients to form a first weighted output signal; a circuit device for forming a masking signal for reducing stereo channel isolation from the first weighted output signal; a second weighting circuit (5) for forming a second weighted output signal weighted with second coefficients from the first low-pass filter output signal or the second low-pass filter output signal according to a switching signal (DD2) indicative of interference in the audio signals; a switch device (4) for selecting the first low-pass filter output signal for weighting in the second weighting circuit means (5) when no interference is indicated by the switching signal (DD2) and the second low-pass filter output signal for weight

Abstract: A circuit arrangement for recognizing adjacent channel interference in a stereo radio receiver, in which a stereo multiplex signal is present. An adjacent channel interference signal is obtained as a function of a direct voltage portion of the stereo multiplex signal and as a function of the spectral components of the stereo multiplex signal above 60 kHz.

Abstract: A noise reduction system and device, and a mobile radio station. Known is a combined Zelinski-spectral subtraction system (1) for noise reduction in a combined speech signal (a(t)) in which signals are recorded with a plurality of microphones (5, 6, 7), using a Wiener filter (10) for estimation of the combined speech signal (a(t)'). In the known system (1) sums and differences of all combinations of speech signals are formed, it being assumed that the differences comprise noise only. Furthermore, a two stage estimation process is carried out, giving rise to considerable estimation errors. An alternative combined Zelinski-spectral subtraction system (1) is proposed, giving rise to fewer estimation errors and being more efficient from a computational point of view. In the Zelinski system, spectral subtraction is carried out on a combined cross spectrum (.PHI..sub.cc).

Abstract: A circuit arrangement for deriving the signal indicating noise in a received stereo multiplex signal, wherein the stereo multiplex signal is present as a digital signal with a first sampling rate that is substantially higher than twice the upper limit of the useful frequency range of the stereo multiplex signal, and the received stereo multiplex signal is passed through a low-pass filter. The low-pass filtered signal and the received stereo multiplex signal are subjected to decimation to a second sampling rate, which is higher than twice the upper limit of the useful frequency range of the stereo multiplex signal. The two stereo multiplex signals with the second sampling rate are subtracted from one another.

Abstract: In a circuit for suppressing short-lived noise phenomena in a digital audio signal, in particular during a temporary test reception of another transmitter, the audio signal is multiplied by a factor which, prior to the appearance of the noise phenomenon, is brought from a maximum value to a minimum value in accordance with a predetermined time function, and at the end of the noise phenomenon, is returned to a maximum value. The invention has special application to the Radio Data System defined by the European Broadcasting Union, and the testing of "Alternative Frequencies" in that system.

Abstract: In a radio receiver with digital signal processing, a stereo multiplex signal received and the useful signals derived therefrom are processed in digital form at a first sampling rate. The subsidiary signals derived from the stereo multiplex signal are at least partly processed at a second sampling rate that is smaller than the first sampling rate. The sampling rate of the processed subsidiary signals are reduced to the first sampling rate with the processed subsidiary signals, acting as control signals with the first sampling rate, affecting the stereo multiplex signal and the useful signals.

Abstract: In a digital circuit which removes ignition noise from a multiplex signal in a radio receiver, especially in a car radio, the multiplex signal is supplied via a high-pass filter (3) and a squaring or absolute value determing circuit (4) as a digital signal with a sampling frequency that is a multiple of the frequency of the pilot tone. The high-pass filtered and squared or absolute value multiplex signal is compared to a short-time mean value of the high-pass filtered and squared (in absolute value) multiplex signal. A control signal S of predetermined duration is formed when deviations occur that are greater than a preset standard. The control signal S controls a correcting circuit in such a manner that sampling values of the multiplex signal occurring during the control signal are replaced with sampling values occurring during the previous period of the pilot tone, thereby masking the ignition noise.

Abstract: Radio receivers which scan through a predetermined band of the radio spectrum, in a station-seeking mode, must independently detect whether the currently tuned frequency is the central frequency of the transmitting station and whether this transmitter provides a signal whose strength is sufficient, i.e. whose strength exceeds a predetermined threshold value. Once these two conditions are satisfied, the radio generates a "stop" signal which terminates the station-seeking mode, i.e. keeps the tuning circuit set to the frequency which provided the sufficiently strong signal. The present invention provides an unusually simple way to determine whether these two conditions are satisfied, by using a Finite-Impulse-Response digital filter (2) to extract a d.c. component of the demodulated signal (MPX), for comparison (6) with a predetermined maximum value, and by filtering (10) a field strength signal (FST), for comparison (11) with a predetermined minimum value.

Abstract: An FM noise reduction circuit including a level detection circuit receiving an intermediate frequency signal. The level detection circuit rectifies the intermediate frequency signal, and outputs a rectified intermediate frequency signal. A first frequency filter passes the rectified intermediate frequency signal in a first frequency range, and outputs a first voltage responsive to the portion of the rectified intermediate frequency signal passed in the first frequency range. A first interference signal detection circuit includes a second frequency filter. The second frequency filter passes the rectified intermediate frequency signal in a second frequency range and outputs a second voltage responsive to the portion of the rectified intermediate frequency signal passed in the second frequency range. The second interference signal detection circuit includes a third frequency filter.

Abstract: A frequency modulation (FM) stereo broadcast receiver detects the onset of multipath interference based on phase changes in the received stereo pilot signal. In a preferred embodiment, the phase of the received pilot signal is compared to the phase of a regenerated pilot from a phase-locked loop in a stereo decoder circuit. The severity of a multipath event is determined by the phase shift detected at the onset of the multipath event.

Abstract: An automotive radio system employs a plurality of corrective actions in response to the detection of multipath interference to reduce distortion audible to a listener. The speed of the vehicle is determined since the number of multipath events per unit time and the expected duration of each multipath event vary according to vehicle speed. The corrective action taken in response to detection of multipath interference depends upon the vehicle speed. In a diversity antenna system, antenna switching is suspended at high vehicle speed while filtering of the audio output to reduce noise is suspended at lower vehicle speeds.

Abstract: An expander circuit for decoding audio signals which were encoded in accordance with the BTSC multichannel sound system standard including DBX commanding is presented. A wideband expander circuit is utilized and a DBX expander can be accommodated. The wideband expander circuit is provided with a signal path having an input LPF (low pass filter), a stereo difference signal (L-R) demodulator, a second LPF, and a voltage controlled amplifier (VCA), the gain of which is controlled by a control signal derived from the demodulated difference signal which has been operated on by a bandpass filter (BPF) and an integrating peak detector. The output of the VCA is provided to a deemphasis network before being fed to a decoder matrix for combining with the sum stereo signal (L+R) for reconstructing the original L and R signals.

Abstract: An expander circuit for decoding audio signals which were encoded in accordance with the BTSC multichannel sound system standard including DBX companding is presented. A wideband expander circuit is utilized and a DBX expander can be accommodated. The wideband expander circuit is provided with a signal path having an input LPF (low pass filter), a stereo difference signal (L-R) demodulator, a second LPF, and a voltage controlled amplifier (VCA), the gain of which is controlled by a control signal derived from the demodulated difference signal which has been operated on by a bandpass filter (BPF) and an integrating peak detector. The output of the VCA is provided to a deemphasis network before being fed to a decoder matrix for combining with the sum stereo signal (L+R) for reconstructing the original L and R signals.

Abstract: An AM stereo receiver in which a synchronous in-phase signal is determined comprises a low pass filter circuit for determining an average DC value of the synchronous in-phase signal, a reference voltage supply for providing a reference voltage indicative of a predetermined portion of the DC value of the synchronous in-phase signal occurring during a 100% IF signal level condition, a comparison circuit for comparing the average DC value of the synchronous in-phase signal to the predetermined reference, and an output circuit outputting a signal indicative of an out-of-lock condition when the average DC value of the synchronous in-phase signal falls below the predetermined reference.

Abstract: A digital radio receiver generates coherent signals for synchronous detection without use of a phase-locked loop by employing an adaptive notch filter to cancel the desired signal. The cancelling signal is employed as the coherent signal for synchronous detection. The invention obtains faster locking to the desired signal, a wider capture range, and more efficient software coding in a digital signal processing receiver.

Abstract: An expander circuit for decoding audio signals which were encoded in accordance with the BTSC multichannel sound system standard including DBX commanding is presented. A wideband expander circuit is utilized and a DBX expander can be accommodated. The wideband expander circuit is provided with a signal path having an input LPF (low pass filter), a stereo difference signal (L?R) demodulator, a second LPF, and a voltage controlled amplifier (VCA), the gain of which is controlled by a control signal derived from the demodulated difference signal which has been operated on by a bandpass filter (BPF) and an integrating peak detector. The output of the VCA is provided to a deemphasis network before being fed to a decoder matrix for combining with the sum stereo signal (L+R) for reconstructing the original L and R signals.