Physics of Sound & Vibration

          An Inter-Disciplinary Resource Website to Effects on Human Electrodynamic Physiology

 

                                     www.uncg.edu/~t_hunter/sound.html

 Main Menu

Site Map

 

Patent No. 6501399  System for creating and amplifying three dimensional sound employing phase distribution and duty cycle modulation of a high frequency digital signal (Byrd, Dec 31, 2002)

Abstract

A method of presenting audio information where changes in amplitude and changes in frequency in two channels (stereo) have the additional parameter of phase information added to re-create the feeling of a live performance. Also, all three parameters are converted into duty cycle modulation of a high frequency digital pulse. Conventional loudspeakers and the brain decode the signal to provide audio signals that contain more information than simply frequency and amplitude changes as a function of time.

Notes:

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to cause harmonics and sub-harmonics to develop for all frequencies, by continuously correcting the phase of the signal logarithmically as a function of frequency, by spatially separating the spectral content of the signal, by increasing the audio bandwidth of the signal, and digitizing the result.

The invention is based, in part, on the recognition that the human hearing mechanism for sensing audio signals (in contrast to electromagnetic and tactile signals) is different from the electronic circuits used to construct amplifiers, microphones, tape recorders, and other types of audio equipment. Thus, when humans hear or sense an audio signal, it is processed differently than standard apparatus attempting to transduce, record, and playback the original signals.

The present invention provides a new way to process and amplify sound in a way that converts amplitude, frequency, and phase information into duty cycle modulation of a high frequency digital pulse. The signal is integrated by the voice coil of ordinary loudspeakers and the phase information is interpreted by the brain so as to provide three dimensional sound. The acoustic hologram so produced is perceived to be like a live performance. Simple digital switching amplifiers can be added to yield any desired power level.

The invention has several objects: to create an expanded bandwidth for recorded (and live) sound in order to take advantage of harmonics outside the "normal" (20-20 khz) hearing range; to create a phase shift of frequencies such that higher frequencies effectively reach the ear after lower frequencies (this creates the three dimensional characteristics of the sounds); to allow natural harmonics to be generated (this provides a sense of being closer to the source); to convert the amplitude, phase, and frequency information into duty cycle modulation of a high frequency digital pulse (>43 KHz) in order to encode the information in a way the ear and loudspeaker can precisely recreate the original information; and to amplify the result with a low distortion, simple, inexpensive amplifier that has no feedback.

In accordance with one aspect of the present invention, an audio signal processor is provided comprising an input terminal for receiving an audio signal, first, second, and third processing stages for processing the audio signal, and an-output terminal for coupling the processed audio signal to an output device. The first and second signal processing stages are arranged in a series or cascade configuration, and each stage functions to phase shift fundamental and harmonic frequencies as a function of frequency. The phase shift increases in a negative direction with increasing frequency, so that higher frequency signals lag the lower frequency signals. Also, the left and right channels are crossed over twice in order to homogenize the signal into phase distributed monaural. The output is then fed into a digital chip that converts the amplitude, frequency, and phase information into a form of duty cycle modulation.

The present invention is implemented by means of a relatively simple electronic circuit that can be manufactured and sold at very low cost. The principal components of the circuit can, if desired, be reduced to a single dual inline package (DIP) which can be incorporated into existing types of audio equipment. The invention can be utilized with nearly all existing types of power amplifiers, stereo tuners, and phonographs with preamplifiers, as well as with compact disk (CD) players, digital audio tape (DAT) players, and conventional analog tape recorders and players. All recorded media can be reproduced with a sound that is close to that of a live performance.

The invention can be used with any number of audio channels or speakers; the resulting sound will be dimensionalized, to some extent, with even a single speaker. The signal processing that is carried out by the present invention transfers to tape and to virtually any other type of recording medium. Thus, for example, a digital CD output can be processed using the present invention, and the result can be recorded on ordinary stereo audio tape. The present invention restores information that has been lost during digital or analog processing, as well as during the transduction of the original sound, and may be employed at a radio or television broadcasting station to improve the quality of the audio signal received by the listeners.