A synchronous read channel having a single chip integrated circuit digital portion which provides digital gain control, timing recovery, equalization, digital peak detection, sequence detection, RLL(1,7) encoding and decoding, error-tolerant synchronization and channel quality measurement is disclosed. The integrated circuit accommodates both center sampling and side sampling, and has a high degree of programmability of various pulse shaping and recovery parameters and the ability to provide decoded data using sequence detection or digital peak detection. These characteristics, together with the error-tolerant sync mark detection and the ability to recover data when the sync mark is obliterated, allow a wide variety of retry and recovery strategies to maximize the possibility of data recovery. Various embodiments, including an embodiment incorporating the analog functions as well as the primary digital functions of the read channel in a single integrated circuit, and preferred embodiments utilizing a reduced complexity, programmable modified Viterbi detector supporting a broad class of partial response channels are disclosed.

Synchronous read channel

Electronic crossover audio systems and methods in accordance with the invention provide flat frequency response and the feeling of three-dimensional music reproduction with a well defined image of the placement of various instruments, the vocal source across the sound stage, and a distinct impression of good depth of feel. A four submodule crossover module capable of serially chaining and having a fourth submodule for front and rear center monaural outputs provides infinite segmentation and modification of incoming audio frequency signals as well as provides for center monaural submodules to supply lifelike musical performances with superior clarity in a three-dimensional imaging.

Audio system for vehicular application

The present invention relates to an auto loudness circuit for performing loudness compensation automatically depending on the signal level. When the signal level decreases, loudness compensation is slowly introduced and as the signal level increases, loudness compensation is quickly removed. To do so, the auto loudness circuit utilizes a filter circuit with the characteristic of a first order bass boost. The filter circuit maintains a corner frequency which is proportional to the inverse of audio level in order to mimic the Fletcher-Munson curves. Because the circuit employs a capacitance-multiplier with a first order resistance capacitance filter, the bass boost is inversely proportional to the signal level. Thus, bass boost is achieved automatically as the program content changes so that the listener is unaware of significant changes in program material as signal levels change either through increase or decrease in volume, crescendo or new material.

System and method for varying low audio frequencies inversely with audio signal level

Differential signals are employed in a distributed audio system to improve noise immunity of the low level differential signals transmitted between a main unit and a power amplifier. The power amplifier may be in an auxiliary output unit which is locally muted by employing a field-effect transistor connected between the differential signals. When the field-effect transistor is turned on by a mute signal, the common mode rejection of the differential amplifier is employed to mute the amplifier output.

Muting circuit using common mode rejection of differential amplifier

An audio system for a vehicle wherein the feeling of a passenger on the rear seat of the vehicle in listening to sound can be improved only by operation of a sound volume switch of a manually operating section without the necessity of operation of any other switch. A microcomputer detects an attenuation amount from an operating section and outputs to an equalizer, when the attenuation amount is lower than a predetermined value, a medium and high frequency sound region controlling signal for attenuating sound in the medium and high frequency sound regions in a substantially inversely proportional relationship at least to the attenuation amount. A plurality of rear loudspeakers receive the medium and high frequency sound region controlling signal from the equalizer and output sound of an attenuation information signal wherein sound in the medium and high frequency sound regions is attenuated.

Audio system for vehicle

A sound system comprises four channels, each having a low level input for coupling to a source of program material, multiple, independently selectable gyrators providing equalization poles, and an input stage for independently and selectively coupling one or more of the gyrators to the low level input. Each channel further includes an amplifier, a buffer for coupling the selected one or more of the multiple gyrators to the amplifier, and a transducer coupled to the amplifier. A filter is coupled between the buffer and the amplifier. The filter has a variable lower corner frequency and a control input terminal. The sound system further comprises a low-pass filter circuit coupled between the amplifier and the control input terminal of the variable corner frequency filter for generating a feedback signal.

David P. Mccorkle

Papers

Automotive sound system