Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1999-07-28
2002-08-06
Lee, Ping (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S061000
Reexamination Certificate
active
06430294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to sound image localization method/apparatus and also a sound image control apparatus. More specifically, the present invention is directed to a sound image localization apparatus and a sound image localization method, capable of localizing a sound image at an arbitrary position within a three-dimensional space, which are used in, for instance, electronic musical instruments, game machines, and acoustic appliances (e.g. mixers). Also, the present invention is directed to a delay amount control apparatus for simulating an inter aural time difference changed in connection with movement of a sound image based upon variation of a delay amount, and also to a sound image control apparatus for moving a sound image by employing this delay amount control apparatus.
2. Description of the Related Art
Conventionally, such a technical idea is known in the field that 2-channel stereophonic signals are produced, and these stereophonic signals are supplied to right/left speakers so as to simultaneously produce stereophonic sounds, so that sound images may be localized. In accordance with this sound image localization technique, the sound images are localized by changing the balance in the right/left sound volume, so that the sound images could be localized only between the right/left speakers.
To the contrary, very recently, several techniques have been developed by which sound images can be localized at an arbitrary position within a three-dimensional space. As one of sound image localization apparatus using this conventional sound image localization technique, an input signal is processed by employing a head related acoustic transfer function so as to localize a sound image. In this case, a head related acoustic transfer function implies such a function for indicating a transfer system defined by such that a sound wave produced from a sound source receives effects such as reflection, diffraction, and resonance caused by a head portion, an external ear, a shoulder, and so on, and then reaches an ear (tympanic membrane) of a human body.
In this conventional sound image localization apparatus, when sounds are heard by using a headphone, first to fourth head related acoustic transfer functions are previously measures. That is, the first head related acoustic transfer function of a path defined from the sound source to a left ear of an audience is previously measured. The second head related acoustic transfer function of a path defined from the sound source to a right ear of the audience is previously measured. The third head related acoustic transfer function of a path defined from a left headphone speaker to the left ear of the audience is previously measured, and the fourth head related acoustic transfer function of a path defined from the right headphone speaker to the right ear of this audience is previously measured. Then, the signals supplied to the left headphone speaker are controlled in such a manner that the sounds processed by employing the first head related acoustic transfer function and the third head related acoustic transfer function are made equal to each other near the left external ear of the audience. Also, the signals supplied to the right headphone speaker are controlled in such a manner that the sounds processed by employing the second head related acoustic transfer function and the fourth head related acoustic transfer function are made equal to each other near the right external ear of the audience. As a consequence, the sound image can be localized at the sound source position.
When the sounds are heard by using speakers, head related acoustic transfer functions of paths defined from the left speaker to the right ear and from the right speaker to the left ear are furthermore measured. While employing these head related acoustic transfer functions, the sounds which pass through these paths and then reach the audience (will be referred to as “crosstalk sounds” hereinafter) are removed from the sounds produced by using the speakers. As a consequence, since a similar sound condition to that of the headphone can be established, the sound image can be localized at the sound source position.
One example of the above-described conventional sound image localization apparatus is shown in FIG.
1
. In
FIG. 1
, a data memory
50
stores a plurality of coefficient sets. Each coefficient set is constructed of a delay coefficient, a filter coefficient, and an amplification coefficient. Each of these coefficient sets corresponds to a direction of a sound source as viewed from an audience, namely a direction (angle) along which a sound image is localized. For instance, in such a sound image localization apparatus for controlling the sound image localization direction every 10 degrees, 36 coefficient sets are stored in this data memory. The externally supplied sound image localization direction data may determine which coefficient set is read out from this data memory. Then, the delay coefficient contained in the read coefficient set is supplied to a time difference signal producing device
51
, the filter coefficient is supplied to a left head related acoustic transfer function processor
52
and also to a right head related acoustic transfer function processor
53
, and further the amplification coefficient is supplied to a left amplifier
54
and a right amplifier
55
.
The time difference signal producing device
51
is arranged by, for example, a delay device, and may simulate a difference between a time when a sound produced from a sound source reaches a left ear of an audience, and another time when this sound reaches a right ear of this audience (will be referred to as an “inter aural time difference” hereinafter). For example, both a monaural input signal and a delay coefficient are inputted into this time difference signal producing device
51
.
In this case, a direction of a sound source as viewed from an audience, namely a direction (angle) along which a sound image is localized will now be defined, as illustrated in FIG.
2
. In this case, it is assumed that a front surface of the audience is a zero (0) degree. In general, an inter aural time difference becomes minimum when the sound source is directed to the zero-degree direction, is increased while the sound source is changed from this zero-degree direction to a 90-degree direction, and then becomes maximum in the 90-degree direction. Furthermore, the inter aural time difference is decreased while the sound source is changed from this 90-degree direction to a 180-degree direction, and then becomes minimum in a 180-degree direction. Similarly, the inter aural time difference is increased while the sound source is changed from the 180-degree direction to a 270-degree direction, and then becomes maximum in this 270-degree direction. The inter aural time difference is decreased while the sound source is changed from the 270-degree direction to the zero-degree (360-degree) direction, and then becomes minimum in the zero-degree direction again. The delay coefficients supplied to the time difference signal producing device
51
own values corresponding to the respective angles.
When the sound image localization direction data indicative of a degree larger than, or equal to 0 degree, and smaller than 180 degrees is inputted, the time difference signal producing device
51
directly outputs this input signal (otherwise delays this input signal only by a predetermined time) as a first time difference signal, and also outputs a second time difference signal delayed from this first time difference signal only by such an inter aural time difference corresponding to the delay coefficient. Similarly, when the sound image localization direction data indicative of a degree larger than, or equal to 180 degrees, and smaller than 360 degrees is inputted, the time difference signal producing device
51
directly outputs this input signal (otherwise delays this input signal only by a predetermined time) as a second time difference signal, and also o
Fujita Akihiro
Kamada Kenji
Kuwano Kouji
Christie Parker & Hale LLP
Kabushiki Kaisha Kawai Gakki Seisakusho
Lee Ping
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