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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.