Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1999-02-08
2002-08-06
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S026000, C381S019000
Reexamination Certificate
active
06430293
ABSTRACT:
DESCRIPTION
The present invention relates to a recording and play-back two-=channel system for providing a holophonic reproduction or playback of sounds.
A holophonic reproduction of sounds involves the capability of detecting, during a sound reproduction or playback operation, the space locations of the sound sources, comprising, for example, musical instruments, in a manner similar to that which would have been obtained if the listening person would have been present at the recording place, for example a theater, and this, tendentially, for any positions of the sound sources with respect to the microphones.
By a holophonic type of reproduction, accordingly, it would be possible to perceive in a home reproduction of a symphonic concert not only the locations of orchestral instruments in front of a listener, but also echoes and reverberations coming from the sides and rear of the listener, as well as related applause.
Thus, the obtained effect substantially corresponds to the effective original sound or musical event.
Several solutions are already known for providing a playback more or less fitted to the sound scene, i.e. the bi/three-dimensional representation of a physical space built-in only by sound information.
All the two-channel stereo recordings, either of a multiple-microphone or a two-microphone type, are suitable to playback, by two diffusers, as in a home stereo system, a more or less suitable reconstruction of an original musical event.
In particular, by a stereophonic recording, each stereo system would be able of recovering a sound scene, which, at most, evolves through the space included between the two diffusers in at least two dimensions, i.e. the right-left dimension between the two diffusers, and the near-far dimension starting from an imaginary line connecting the two diffusers, and progressively away from a listening point.
The sole condition to be met by a listener in order to obtain a satisfactory stereophonic effect is to be located ideally at the apex of an equilater triangle, the two other apex points thereof are occupied by the two diffusers.
A bi-three-dimensional representation of a physic space built-in only based on a sound information obtained from a stereophonic system, can evolve through a generally trapezoidal region, where the small base apex points are closer to the listener and are represented by the two diffusers of the system, whereas the apex points of the major base are represented by two points defined by a sound information contents of the recording, such as phase delays and reverberations, sound reflections caused by a home listening room as well as the detecting properties of the diffusers or sound emitting sources.
The above disclosed region is defined as a “sound or acoustic range”. By exploiting the high sensitivity of an earing system to phase and frequency response variations, it would be however possible, by a suitable electronic apparatus, to broaden, during the recording operation, the sound range, as reproduced by a stereophonic system, or the area in which it would be possible to reconstruct the virtual sound scene, i.e. that area in which it would be possible to form and perceive again virtual sound subjects, since the latter would be present in said recording.
This technique, which is used, for example, in the so-called Q discs, will always held the positions of the diffusers and of the listening point consistant, thereby theoretically providing a sound field about a the listener.
In order to further broaden the sound range, other two-channel recording and playing-back systems have been made: the so-called quadriphony, i.e. four independent channels, two at the front and two at the rear; the “Dolby-Surround” and all the improvement variations thereof, with four playback channels, i.e. three front channels, central right and left channels, as well as the rear monochannel splitted on two diffusers, and yet other systems including more than four recording and playback channels such as the “Dolby AC3”.
These prior systems, which provide to use, during the recording operation, multiple-microphone techniques and electronic signal processing methods, would allow to broaden up to 360° the sound field with at least three channels during the recording and for diffusers during the playback.
Thus, it would be possible to locate sound objects outside the most marked and clean areas of the sound field using only channels with phase rotation and two diffusers, like the above disclosed technique, and as it occurs in the so-called Q-discs.
While the above mentioned prior recording and playback systems solve the mentioned technical problem of a holophonic sound reproduction, they have, however, the disadvantages of an excessively reduced sound field area, actually preventing a true and proper holophonic reproduction.
The Q-disc system, on the other hand, provides a rather unnatural effect due to an insufficient capability of locating the sound subjects the space arrangement of which must be considered with respect to the sound field area.
This derives from several reasons, the main of which is that said diffusers are anyhow perceived as a sound emitting source by a listener, thereby providing a perspective distortion effect.
A sound recorded by a conventional stereophonic method, the original features of which would be such as to always bring that sound to be perceived outside the sound field area, would be anyhow tendentially returned to said area, since the reproduced sound emission occurs at the points occupied by the diffusers. In order to broaden the sound field area, it would be necessary in this case to offset the mentioned prospective distortion by suitable phase rotations and frequency response modifications which, since would not correspond to those naturally perceived for a sound just coming from that space point and, accordingly, would be unnatural. Moreover, during a recording operation, it would be necessary to provide an electronic apparatus for modifying the signal from the microphones and electronic sources, for example an electric guitar which, while perfect, would however introduce distortions in the signals, thereby worsening the reproduced sound quality.
The multiple channel recording and playback system, moreover, involves a coding operation, during the recording operation, in order to include more than two channels in the single two-channel arrangement of the stereophonic software, in addition to a decoding step during the playback operation. While the compatibility with a stereophonic system is satisfactory, the sound field will fall into the sound field area disclosed for the two channel systems, admitted that the playback system is of a stereophonic type.
A further disadvantage is the requirement of coding and decoding recorded signals by an electronic apparatus, which will further distort an original signal.
Moreover, each system including more than two recording channels can not contain, by definition, phase information and frequency response variations like those which would allow a human ear system to reconstruct a sound scene identical to that which would be perceived as present in a original sound event.
Furthermore each effort to broaden the sound field would involve an use of auxiliary electronic apparatus such as phase processors and coders, at least in a recording operation, which apparatus, in addition to worsening the signal quality, would have a very high cost for the required software: discs, CD, and so on.
SUMMARY OF THE INVENTION
Accordingly, the aim of the present invention is to overcome the above mentioned prior art drawbacks.
In order to achieve the above mentioned aim, the present invention provides a two-channel sound recording and playback system, suitable to provide a holophonic reproduction of sounds which is constructionally simple, of low cost and provides an end playback result which is more natural and realistic than that obtained by recording and playback sounds by three of more channels, thereby providing a sound reproduction which is substantially identical to the original sound
Hedman & Costigan ,P.C.
Mei Xu
LandOfFree
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