Electrical audio signal processing systems and devices – Binaural and stereophonic – Stereo sound pickup device
Reexamination Certificate
1999-12-28
2004-08-24
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Stereo sound pickup device
C381S122000, C381S061000
Reexamination Certificate
active
06782104
ABSTRACT:
The stereophonic recording and playback of sounds has been known for some time.
Sound is picked up by at least two microphones fixed in a precise position and orientation and considered to be “strategic” with respect to the sound source.
The sounds coming from one of these two microphones, or from a set of microphones, are recorded on one track while the sounds coming from the second microphone, or from the second set of microphones, are recorded on another track, distinct from the first one.
Recorded sounds are played back by at least two speaker boxes (or loudspeakers) suitably positioned and oriented.
The binary nature of any stereophonic system comes from the transposition to sound of stereoscopy, dating back earlier, and itself based on the binocular vision of man.
While the optical systems that make use of this binocular vision, holograms, bipolar images or anaglyphs, for example, reproduce visual relief fairly well (at the expense of using many artifices, however), the same is not true of stereophonic systems, because of their very simplicity based on the fact that, naturally, man hears all the sounds in space from two sources alone.
In other words, all complex sounds distributed through a three-dimensional space, including different levels, are reduced to a single plane, joining together the speaker boxes and at their level alone.
This simplification is generally accepted because the human brain reconstitutes a true space virtually, particularly through the balance that is deliberately constructed between different sound sources, so that the listener has, or rather believes he has, an impression of relief.
It is not necessary to go into detail on the statement that relief implies three dimensions and not two, and it is easy to understand that, however far one goes in improving ad-hoc sound reproduction, stereophony has its own limitations simply because it limits the number of sound sources offered to the listener's hearing to two, themselves subject to the limitation on recording tracks, with no possibility of a third dimension.
To give context to the State of the Art, the following documents may be cited:
Article by Mr A Laracine published in the journal “ZERO VU”, pages 40, 42, 44, 46, 47 and 48, which states that . . . “stereophony is only one stage” and that “the listener does not always find in it the opportunity for intelligent listening, but nevertheless the main ones and a large part of his liberty, and therefore his listening comfort”,
The author also points out that, in the case of orchestral music, . . . “if the general balance of the work has been obtained by the sound recordist, thanks to good positioning of the microphone, any other major action taken (level, corrections, difference in presence) will be experienced as a sort of “pleonasm” of sound and will distract the listener's attention”. And, further on: “One solution consists in using cardioid microphones positioned 17 cm apart, their axes forming an angle of 110° between them. All calculations, all measurements and the very numerous experiments all combine to prove that this system is the best possible compromise. It is known by the system name AB O.R.T.F. since it was developed in the acoustic laboratory of the former O.R.T.F.”
Naturally, all known recording systems concern positioned microphones, fixed once and for all throughout the recording. This is demonstrated by this extract from the same article:” . . . in the case of the picking up of sounds that are close together, a “tearing apart” of space is observed. This tearing apart is the same as that experienced by a spectator (sic) if he approaches the sound sources in the same way”. Since the number of sound sources is always equal to two and since they occupy a fixed position from which they cannot be removed, the angle at which the listener perceives the sounds coming from these two sources varies depending on the space he occupies in relation to them and . . . “the difficulty arises from the fact that it is not possible to ask a listener to move closer to his speaker boxes temporarily. It is therefore necessary to find ways of creating faults with the O.R.T.F. pair to compensate for its unsuitability for certain situations. It is possible . . . to cause the pair to pivot on its axis in order to cause it to occupy an intermediate position between the horizontal plane and the vertical plane”.
The existence of an occupied position clearly demonstrates, here too, that the pair is positioned and fixed.
In the Internet publication, at the address http:\\www.stereolith.ch, entitled “Stereolith® systme”, the following is stated: “During a stereophonic recording, the sound space is encoded by a two-channel (dipole) matrix. For this, a pair of microphones is used, for example. Each of the microphones provides a signal that is slightly different depending on the location of the sound source. This slight difference is of great importance. The spaciousness of the recording is depends solely on this difference.” And further on: “In modem electronic music the vital sound space is produced in the studio, by means of special three-dimensional (sic) processors.”
This same publication contains the following information regarding listening by means of speaker boxes: “Outside the ideal listening point, it is impossible for our brain to reconstitute the sound image: the elementary information is missing or distorted. This means that, very often, we obtain merely bi-channel reproduction rather than stereophonic reproduction”.
The document published by Schoeps GmbH, Spitalstr. 20, 7500 Karlsruhe 41 (Germany) describes a pair of microphones associated with a sphere based on the human head, which constitutes an assembly that has to be fixed to a “strategic” location: “The new approach should take account of all the parameters characterising the sound source and its location”. This therefore definitely relates to an immobile sound source, situated in a given location relative to the pair of microphones, which is itself immobile. The technical specification of this apparatus requires, furthermore, that the sound pick-up angle is fixed at around 90° and that there is:
an accessory supplied with the device itself, which is an “accessory for suspending the microphone with a ball joint. Total weight: around 0.5 kg”.
“a ball joint for mounting on a stand”.
Spheres carrying two microphones do exist in different variants, one of which is described in the patent document EP 0 050 100, all providing improvements to the structure of the sphere, in order to bring it as close as possible to a genuine human head, in the hope of making the recording conditions coincide with the listening conditions but, as has been indicated above, the limitation of stereophony is in its binary nature and, therefore, in the static situation of the microphones and speaker boxes, located respectively upstream and downstream of the recording tracks.
Patent document FR 2 290 811, which describes a piece of apparatus for picking up sounds intended to eliminate sounds considered to be interference in comparison with those that are intended to be picked up, this device comprising just one or two microphones, depending on whether the apparatus is intended for a single person or for two. One example of using this apparatus is for the direct transmission, without recording, of words spoken by one or two people located in a moving vehicle, by means of powerful loudspeakers. Another example of the use of this apparatus is to integrate it into a loudspeaker-type telephone.
The result sought is the purity of the transmitted sounds, obtained by eliminating echo, ambient noise and open-air sounds.
Patent document DE 1 239 355, which describes a piece of apparatus comprising a stand and two microphones that can be oriented with respect to a support fixed to the stand. This apparatus is therefore fixed and its microphones are capable of movement with respect to the place where the apparatus is placed.
Patent document EP 0 186 996, which describes a microphone with a particular structure allowing
ARKAMYS
Isen Forester W.
Notaro & Michalos P.C.
Pendleton Brian
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