Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1998-09-04
2001-09-04
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S098000, C381S001000, C381S106000
Reexamination Certificate
active
06285767
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 the perceived low-frequency content of acoustic energy produced by an acoustic transducer, such as a loudspeaker.
BACKGROUND
The audio and multimedia industries have continually struggled to overcome the imperfections of reproduced sound. For example, it is often difficult to adequately reproduce low-frequency sounds such as bass. Various conventional approaches to improving the output of low-frequency sounds include the use of higher quality speakers with greater cone areas, larger magnets, larger housings, or greater cone excursion capabilities. In addition, conventional systems have attempted to reproduce low-frequency sounds with resonant chambers and horns that match the acoustic impedance of the loudspeaker to the acoustic impedance of free space surrounding the loudspeaker.
Not all systems, however, can simply use more expensive or more powerful speakers to reproduce low-frequency sounds. For example, some conventional sound systems such as compact audio systems and multimedia computer systems rely on small loudspeakers. In addition, to conserve costs, many audio systems use less accurate loudseakers. Such loudspeakers typically do not have the capability to properly reproduce low-frequency sounds and consequently, the sounds are typically not as robust or enjoyable as systems that more accurately reproduce low-frequency sounds.
Some conventional enhancement systems attempt to compensate for poor reproduction of low-frequency sounds by amplifying the low-frequency signals prior to inputting the signals into the loudspeakers. Amplifying the low-frequency signals delivers a greater amount of energy to the loudspeakers, which in turn, drives the loudspeakers with greater forces. Such attempts to amplify the low-frequency signals, however, can result in overdriving the loudspeakers. Unfortunately, overdriving the loudspeakers can increase the background noise, introduce distracting distortions, and damage the loudspeakers.
Still other conventional systems, in an attempt to compensate for the lack of the lower-frequencies, distort the reproduction of the higher frequencies in ways that add undesirable sound coloration.
SUMMARY OF THE INVENTION
The present invention provides a unique apparatus and method that enhances the perception of low-frequency sounds. In loudspeakers that do not reproduce certain low-frequency sounds, the invention creates the illusion that the missing low-frequency sounds do exist. Thus, a listener perceives low frequencies, which are below the frequencies the loudspeaker can actually accurately reproduce. This illusionary effect is accomplished by exploiting, in a unique manner, how the human auditory system processes sound.
One embodiment of the invention exploits how a listener mentally perceives music or other sounds. The process of sound reproduction does not stop at the acoustic energy produced by the loudspeaker, but includes the ears, auditory nerves, brain, and thought processes of the listener. Hearing begins with the action of the ear and the auditory nerve system. The human ear may be regarded as a delicate translating system that receives acoustical vibrations, converts these vibrations into nerve impulses, and ultimately into the “sensation” or perception of sound.
The human ear is known to be non-linear in its response to acoustic energy. This non-linearity of the hearing mechanism produces intermodulation distortion in the form of additional overtones and harmonics, which do not exist in the actual program material. These non-linear effects are particularly pronounced at low frequencies and these effects have a pronounced effect on how low-frequency sounds are perceived.
Advantageously, some embodiments of the invention exploit how the human ear processes overtones and harmonics of low-frequency sounds to create the perception that non-existent low-frequency sounds are being emitted from a loudspeaker. In some embodiments the frequencies in higher-frequency bands are selectively processed to create the illusion of lower-frequency signals. In other embodiments, certain higher-frequency bands are modified with a plurality of filter functions.
In addition, some embodiments of the invention are designed to improve the low-frequency enhancement of popular audio program material, such as music. Most music is rich in harmonics. Accordingly, these embodiments can modify a wide variety of music types to exploit how the human ear processes low-frequency sounds. Advantageously, music in existing formats can be processed to produce the desired effects.
This new approach produces a number of significant advantages. Because a listener perceives low-frequency sounds, which do not actually exist, the need for large speakers, greater cone excursions, or added horns is reduced. Thus, in one embodiment, small loudspeakers can appear as if they are emitting the low-frequency sounds of larger speakers. As can be expected, this embodiment produces the perception of low-frequency audio such as bass, in sound environments that are too small for large loudspeakers. Large loudspeakers are benefited as well, by creating the perception that they are producing enhanced low-frequency sounds.
In addition, with one embodiment of the invention, the small loudspeakers in hand-held and portable sound systems can create a more enjoyable perception of low-frequency sounds. Thus, the listener need not sacrifice low-frequency sound quality for portability.
In one embodiment of the invention, lower-cost speakers create the illusion of low-frequency sounds. Many low-cost loudspeakers cannot adequately reproduce low-frequency sounds. Rather than actually reproducing low-frequency sounds with expensive speaker housings, high performance components and large magnets, one embodiment uses higher frequency sounds to create the illusion of low-frequency sounds. As a result, lower-cost speakers can be used to create a more realistic and robust listening experience.
Furthermore, in one embodiment, the illusion of low-frequency sounds creates a heightened listening experience that increases the realism of the sound. Thus, instead of the reproduction of the muddy or wobbly low-frequency sounds existing in many low-cost prior art systems, one embodiment of the invention reproduces sounds that are perceived to be more accurate and clear. Such low-cost audio and audio-visual devices can include, by way of example, radios, mobile audio systems, computer games, loudspeakers, compact disc (CD) players, digital versatile disc (DVD) players, multimedia presentation devices, computer sound cards, and the like.
In one embodiment, creating the illusion of low-frequency sounds requires less energy than actually reproducing the low-frequency sounds. Thus, systems which operate on batteries or in low-power environments, can create the illusion of low-frequency sounds without consuming as much valuable energy as systems which simply amplify or boost low-frequency sounds.
Other embodiments of the invention create the illusion of lower-frequency signals with specialized circuitry. These circuits are simpler than prior art low-frequency amplifiers and thus reduce the costs of manufacturing. Advantageously, these cost less than prior art sound enhancement devices that add complex circuitry.
Still other embodiments of the invention rely on a microprocessor, which implements the disclosed low-frequency enhancement techniques. In some cases, existing processing audio components can be reprogrammed to provide the disclosed unique low-frequency signal enhancement techniques of one or more embodiments of the invention. As a result, the costs of adding low-frequency enhancement to existing systems is significantly reduced.
In one embodiment, the sound enhancement apparatus receives one or more input signals, from a host system and in turn, generates one or more enhanced output signals. In
Isen Forester W.
Knobbe Martens Olson & Bear LLP
Pendleton Brian Tyrone
SRS Labs, Inc.
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