Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1997-06-17
2001-08-28
Isen, Forester W. (Department: 2644)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S258000, C330S069000, C381S099000, C381S001000
Reexamination Certificate
active
06281749
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to audio enhancement systems and methods for improving the realism of sound reproduction. More particularly, this invention relates to apparatus and methods for enhancing a pair of audio signals to create an immersive, three-dimensional effect when the audio signals are acoustically reproduced.
BACKGROUND
The audio and multimedia industries have continually strived to overcome the imperfections of reproduced sound. For example, a common imperfection is that the recording of sounds emanating from multiple locations is not properly reproduced in an audio system. One approach directed to improving the reproduction of sound includes surround sound systems which have multiple recording tracks. The multiple recording tracks are used to record the spatial information associated with sounds which emanate from multiple locations.
For example, in a surround sound system, some of the recording tracks contain sounds which are intended to originate from in front of the listener, while other recording tracks contain sounds which are intended to originate from behind the listener. When multiple speakers are placed around the listener at positions representing the intended origin of the recorded sounds, the audio information contained in the recording tracks makes the produced sounds appear more realistic to the listener. Such systems, however, are typically more expensive than systems which do not use multiple recording tracks and multiple speaker arrangements.
To conserve costs, many conventional two-speaker systems attempt to simulate a surround sound experience by introducing unnatural time-delays or phase-shifts between left and right signal sources. Unfortunately, such systems often suffer from unrealistic effects in the reproduced sound.
Other known sound enhancement techniques operate on what are called “sum” and “difference” signals. The sum signal, which is also called the monophonic signal, is the sum of the left and right signals. This can be conceptionalized as adding or combining the left and right signals (L+R).
The difference signal, on the other hand, represents the difference between the left and right audio signals. This is best conceptionalized as subtracting the right signal from the left signal (L−R). The difference signal is also often called the ambient signal.
It is known that modifying certain frequencies in the difference signal can widen the perceived sound projected from the left and right speakers. The widened sound image typically results from altering the reverberant sounds which are present in the difference signal. Sound enhancement techniques which process sum and difference signals is disclosed in U.S. Pat. Nos. 4,748,669 and 4,866,774, both issued to Arnold Klayman, one of the inventors for the invention disclosed in the present application.
In existing sound enhancement systems which process the sum and difference signals, the sum and difference signals are generated from circuitry which combines the left and right input signals. In some systems, once the circuitry generates the sum and difference signals, additional circuitry then separately processes and recombines the sum and difference signals in order to produce an enhanced sound effect. For example, the sound system disclosed in U.S. Pat. No. 4,748,669 has a sum and difference signal generator. Also, the sound system disclosed in U.S. Pat. No. 4,308,423 has a difference signal generator.
Typically, the creation and processing of the sum and difference signals are accomplished with digital signal processors, operational amplifiers and the like. Such implementations usually require complicated circuitry which increases the cost of such systems. Thus, despite the contributions from the prior art, there exists a need for a simplified audio enhancement system which reduces costs associated with producing an enhanced listening experience.
SUMMARY OF THE INVENTION
The present invention provides a unique apparatus and method which simplifies the enhancement of audio information and provides a widened stereo image. This is accomplished by correcting the perspective of audio information through the modification of the differential information existing in the audio information. Advantageously, the preferred sound enhancement system uses fewer components than the prior art sound enhancement systems and thus reduces the costs of enhancing audio signals. As a result, the preferred sound enhancement apparatus is easy to manufacture and costs less than many other sound enhancement devices.
In addition, the preferred sound enhancement apparatus enhances audio information without generating discrete sum and difference signals. As a result, the preferred embodiment does not need the complex circuitry which processes audio input signals to generate intermediate signals which are then separately processed and recombined to generate enhanced output signals. Advantageously, the preferred embodiment can be used to enhance sound in a wide range of low-cost audio and audio-visual devices which by way of example can include radios, mobile audio systems, computer games, multimedia presentation devices and the like.
Broadly speaking, the sound enhancement apparatus receives at least two input signals, from a host system and in turn, generates two enhanced output signals. In particular, the two input signals are processed collectively to provide a pair of spatially corrected output signals. In addition, the preferred embodiment modifies the audio information which is common to both input signals in a different manner than the audio information which is not common to both input signals.
The audio information which is common to both input signals is referred to as the common-mode information, or the common-mode signal. The common-mode audio information differs from a sum signal in that rather than containing the sum of the input signals, it contains only that audio information which exists in both input signals at any given instant in time. In addition, the preferred embodiment reduces the amplitude of the frequencies in the common-mode signal in order to reduce the clipping which may result from high-amplitude input signals.
In contrast, the audio information which is not common to both input signals is referred to as the differential information or the differential signal. Although the differential information is processed in a different manner than the common-mode information, the differential information is not processed to form a discrete signal. Rather, the common-mode and differential information are processed together.
As discussed in more detail below, the sound enhancement system spectrally shapes the differential signal with a variety of filters to create an equalized differential signal. By equalizing selected frequency bands within the differential signal, the sound enhancement apparatus widens a perceived sound image projected from a pair of loudspeakers placed in front of a listener.
As discussed in more detail below, the preferred sound enhancement apparatus includes two transistors which are interconnected at their emitters and their collectors with multiple cross-over networks. Preferably, the cross-over networks act as filters which equalize desired frequency ranges in the differential input. Thus, the differential gain varies based on the frequency of the input signals.
Because the cross-over networks equalize the frequency ranges in the differential input, the frequencies in the differential signal can be altered without affecting the frequencies in the common-mode signal. As a result, the preferred embodiment can create enhanced audio sound in an entirely unique and novel manner.
The preferred sound enhancement apparatus is in turn, connected to one or more output buffers. The output buffers isolate the sound enhancement apparatus from other components connected to the first and second output signals. For example, the output signals can be directed to other audio devices such as a recording device, a power amplifier, a pair of loudspeakers an
Klayman Arnold I.
Kraemer Alan D.
Isen Forester W.
Knobbe Martens Olson & Bear LLP
Pendleton Brian Tyrone
SRS Labs, Inc.
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