Electrical audio signal processing systems and devices – Binaural and stereophonic – Stereo sound pickup device
Reexamination Certificate
2000-11-22
2003-01-14
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Stereo sound pickup device
C381S092000, C381S111000
Reexamination Certificate
active
06507659
ABSTRACT:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF THE INVENTION
This invention relates to a microphone assembly consisting of three or more microphone elements that are arranged to achieve a surround image for recording audio, especially audio synchronized with video. The outputs of the invention are compatible with current surround decoders.
BACKGROUND OF THE INVENTION
Prior art multiplexing systems for reducing more than two audio channels to two audio channels are replete in the art. Common practice in this area involves encoding a two channel or stereo recording by means of multiplexing in order to establish more than two channels of sound in the two channel recording, which extra channels of sound typically are retrieved by a complementary reversal of the encoding process. The most notable is the system licensed under the trademark DOLBY PROLOGIC. Usually, a recording is encoded with a DOLBY SURROUND SOUND brand system for subsequent playback on a system equipped with a complementary proprietary decoding circuit which extracts so-called “matrixed” information from the recording for playback through left, right, center, and rear speakers. This is a relatively simple process compared to the more complex quadraphonic matrixing systems of past. This proprietary system has grown in popularity due to prominence of encoded source material such as movies having surround sound soundtracks. More importantly, however, the DOLBY PROLOGIC brand decoder, along with the predecessor, the DOLBY SURROUND brand decoder, is compatible with playback of conventional stereo recordings and other sources and can provide pleasant results, especially with recordings having notable ambient content (e.g. recordings produced with a pair of microphones, one corresponding to one of the two stereo channels in the recording). This proprietary decoding process produces four channels of sound from the two channel input of a stereo recording or other source: Left, Right, Center, and Surround. The DOLBY standard includes additional parameters and specifications for the encode/decode process, such as bandwidth filters and delay, but it can be seen that decoding essentially consists of summing the Left and Right channels of stereo recording to produce the third “Center” channel, and subtracting the Left channel information from the Right channel information to derive the fourth “Surround” channel. The Surround channel thus essentially consists of information which is inherently out of phase between the Left and Right channels (i.e. generally a difference of 180 degrees). This encoding process makes use of the natural ability of the ear to perceive out-of-phase audio information to artificially create the Surround channel and store it as ambient or out-of-phase information on the Left and Right channels. Naturally, any out-of-phase or ambient information contained on a conventional stereo recording, such as a stereo recording of an orchestra, is also extracted by such a prior art decoder during playback and accordingly reproduced as “surround” channel information, but not to any discernable degree, due to lack of strength of the out-of-phase signal. Similarly, “center” channel information contained on a conventional stereo recording or other source may be exaggerated when decoded during playback with this system's decoder due to excessive center stage content contained in the conventional stereo recording.
Many microphone assemblies are known for monophonic and stereophonic recording, which assemblies can include a single or pair of microphone elements. Such prior art microphone assemblies are limited in their ability to reproduce a full, two dimensional sound field and in their ability to localize sound. While other microphone assemblies with more than two microphone elements can reproduce relatively full, two dimensional sound fields and can localize sounds, their outputs are not compatible with standard surround decoders. Also, they are deficient in their ability to reproduce what may be called a staging effect or surround image, which would be compatible with DOLBY SURROUND technology.
There is a need, therefore, for a microphone apparatus which can cheaply and reliably produce a surround image (as defined below), localize sounds and remain compatible with standard surround decoders.
Prior developments in this field may be generally illustrated by reference to the following U.S. Patent documents:
U.S. Patent Documents
Patent No.
Patentee
Issue Date
4,206,324
Horikawa et al.
Jun. 3, 1980
4,262,170
Bauer
Apr. 14, 1981
3,872,249
Takahashi et al.
Mar. 18, 1975
4,072,821
Bauer
Feb. 7, 1978
3,845,245
Takahashi
Oct. 29, 1974
4,680,796
Blackmer et al.
Jul. 14, 1987
5,027,403
Short et al.
Jun. 25, 1991
4,841,573
Fujita
Jun. 20, 1989
3,856,992
Cooper
Dec. 24, 1974
4,947,437
Firebaugh
Aug. 7, 1990
The disclosures of the above patent documents are incorporated herein by reference.
U.S. Pat. No. 3,872,249 shows a circuit for decoding an encoded or matrixed signal on a stereo channel (i.e. Left and Right channels) based on a known variable mixing ratio for matrixing at least four sound channels (i.e., Left Front, Right Front, Left Rear, and Right Rear). Passing similarity with the present invention lies in the general teaching of matrixing more than two channels into a two channel medium. In the case of the instant invention, however, no forced phase shifting (i.e. by use of electronics) occurs, as it does in this reference. Also, a multi-channel recording device, along with a multi-channel mixer, generally are required to produce an acceptable multi-channel recording in this reference.
U.S. Pat. No. 4,206,324 discloses a multi-element microphone assembly in which two microphone side element supports are pivotally disposed relative to a center fixed element support. The side supports are pivotally adjustable relative to the center fixed element, and the output levels of the side elements are electrically adjustable relative to the center element output. This reference does not show a rear microphone element, nor a matrixing circuit for four microphone elements.
U.S. Pat. No. 4,262,170 teaches a microphone system and circuitry for encoding multi-channel sound information picked up by its microphones into two channels (i.e. Left and Right) for subsequent playback by an SQ type quadraphonic sound system. Similarity with the present invention lies in the general teaching of a microphone apparatus and circuitry for encoding multiple channels into two channels, but the reference teaches subsequent playback on a system with complementary decoding. The actual circuit itself in one embodiment relies on signal phase shifting and amplification to encode the multiple channels, whereas the present circuit relies on signal amplification only. Other embodiments of this reference show various frequency-dependent phase-shifting and amplitude-adjusting circuits. The system of the present invention inherently incorporates natural phase shift in that information received by the rear microphone hereof generally is out-of-phase with the center microphone, in relation to the recording site. This reference further notes that Neuman Company of West Berlin, Germany, manufactures a 4-element adjustable microphone assembly.
U.S. Pat. No. 4,947,437 to Firebaugh teaches the use of a four-quadrant photoelectric microphone to produce unencoded stereo signals, which signals (apart from their creation by photoelectrically measuring acoustical displacement of a suspended ball at a single point in space) are entirely conventional stereo. That is to say, only combined center/left and combined center/right audio information is passed on to the left and right output signals, the rear audio information being subtracted out. The Firebaugh device does not encode and preserve surround information, as defined infra. A missing feature in Firebaugh (and other art) is the orientation of the microphone elements as related to 4-2-4 matrix inputs, which is required to acoustically capture the sound local to a camera in a way that when encoded wit
Iredale John J.
Keller Roger S.
Cascade Audio, Inc.
Grier Laura A.
Isen Forester W.
Johnson Larry D.
Johnson & Stainbrook LLP
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