Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
1998-10-29
2002-11-26
Mai, Tan V. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
C708S316000
Reexamination Certificate
active
06487572
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved digital filtering method and device which permit efficient filtering processing where filtering arithmetic operations are executed every plurality of samples in an intermittent manner, and a sound image localizing device which, using the improved digital filtering method, can suitably impart a high-quality sound image localization effect to sound waveform data.
A variety of sound image localizing devices have been developed and marketed in recent years, to achieve sounds full of a sense of “presence”. As a system intended for use in movies, music concerts and the like, the so-called “5.1 channel technique” has been standardized, according to which three-channel speakers are placed before listeners and two-channel speakers are placed behind the listeners and volumes and phases of sounds generated from each of the speakers are adjusted in accordance with movement of a sound source.
As another technique, the three-dimensional positioning system has been known, according to which a head-related transfer function (abbreviated “HRTF”), indicative of a sound transfer from a sound source to listener's left and right ears, is measured previously in association with possible coordinates of the sound source and a coefficient of the head-related transfer function (HRTF) is varied dynamically as the coordinates of the sound source changes. With this three-dimensional positioning system, the overall system organization can be greatly simplified because only two-channel speakers and amplifiers corresponding to the left and right ears are sufficient for sound generation purposes.
FIG. 6
is a functional block diagram of a typical example of the three-dimensional positioning system. In the illustrated example, the three-dimensional positioning system employs three sound sources SG
1
, SG
2
and SG
3
which generate waveform data W
1
, W
2
and W
3
, respectively. The positioning system also includes finite impulse response (FIR) filters, and characteristics of each of these FIR filters F
1
to F
3
represents a head-related transfer function (HRTF) representative of a sound transfer from a sound source to listener's left and right ears. Here, as the sound sources SG
1
, SG
2
and SG
3
move imaginarily, respective coefficients of the FIR filters F
1
to F
3
are varied dynamically in accordance with the changing coordinates of the sound sources SG
1
, SG
2
and SG
3
.
The positioning system of
FIG. 6
further includes adders A
1
and A
2
, which add together output data from the FIR filters F
1
to F
3
so as to provide waveform data for the left (L) and right (R) channels. Note that the waveform data are generated from the adders A
1
and A
2
in accordance with the head-related transfer functions (HRTFs) assuming that sounds from the sound sources SG
1
, SG
2
and SG
3
are input directly to the left and right ears. Thus, no particular problem would arise if sound generator means are placed very close to the listener's left and right ears and a sound from each of the sound generator means is listened to by only one of the two as in the case of headphones; however, if the left-and right-channel speakers are placed before the listener, then a sound from one of the speakers would reach both of the left and right ears, thereby causing unwanted crosstalk. Thus, a crosstalk processing section C is used in the illustrated example to generate left-channel waveform data DL and right-channel waveform data DR modified to cancel aural influences of the crosstalk. Note that whereas the operations up to those of the adders A
1
and A
2
are performed separately for each of the sounds, the crosstalk processing operations are performed collectively on all of the sounds.
Further,
FIG. 7
is a block diagram showing a detailed construction of the FIR filter F
1
employed in the system of FIG.
6
. Assuming that the three-dimensional positioning system is provided within a personal computer, the FIR filter F
1
is connected to a host driver (not shown) via a PCI (Peripheral Component Interconnect) bus unit or the like, and includes a DSP (Digital Signal Processor)
100
for performing arithmetic operations, such as multiplication and addition, a CPU
200
for controlling the DSP
100
, a working memory
210
connected to the CPU
200
and an HRTF coefficient data memory
110
storing therein HRTF or head-related transfer function coefficient data. Thus, once a coordinates instruction P is given from the host driver via the bus unit to the FIR filter F
1
, the CPU
200
, using the working memory
210
, calculates an address indicating a storage region of HRTF coefficient data h corresponding to individual tap coefficients of the filter and sends the thus-calculated address to the DSP
100
. Then, the DSP
100
reads out the HRTF coefficient data h from the HRTF coefficient data memory
110
and performs multiplication and addition operations between the HRTF coefficient data h and waveform data W
1
, so as to generate processed waveform data W
1
′.
Directional accuracy with which the sound source is to be localized depends on a data quantity of the HRTF coefficient data h. Therefore, for increased accuracy of sound image localization to achieve sounds full of a sense of presence, there has been a need to provide a great-capacity HRTF coefficient data memory
110
in the FIR filter F
1
. Further, because the conventional system has to interpret the coordinates instruction P given from the personal computer and thereby selectively read out the HRTF coefficient data h, there has been a need to provide the CPU
200
within the FIR filter F
1
as a controller. Besides, because the host driver, in many cases, is provided with a CPU for controlling the overall operations of the personal computer and a great-capacity main memory, etc., the conventional system would encounter the problem that an overall size of electric circuitry in the FIR filter unavoidably increases and the circuit arrangements of the host driver can not be used effectively.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a digital filtering method and device which are operable by being connected a computer bus and which achieve efficient digital filtering processing without increasing a size of electric circuitry employed.
It is another object of the present invention to provide a sound image localizing device which achieve high-quality sound image localization control without increasing a size of electric circuitry employed.
In order to accomplish the above-mentioned object, the present invention provides a digital filtering method which comprises: a first step of collectively transferring, via a bus of a computer, a plurality of samples of digital data to be filtered; a second step of executing filtering processing, based on a predetermined filter function, on the plurality of samples of digital data transferred by the first step, at a processing rate higher than a predetermined sampling rate; and a third step of buffering the digital data having been subjected to the filtering processing by the second step and then outputting, at the predetermined sampling rate, the digital data buffered thereby.
Because of the arrangement that a plurality of samples of digital data to be filtered are transferred collectively via the computer bus, it is possible to eliminate a need for the computer to send out the digital data in synchronism with a predetermined sampling cycle, and thus the digital data transfer is not substantially bound by time. As a consequence, the computer and bus can be used efficiently for any other purpose. Further, because the filtering processing by the second step carries out filtering arithmetic operations based on a predetermined filter function at a rate higher than a predetermined sampling rate, the filtering arithmetic operations, in an exemplary case where f samples of the digital data are to be filtered, can be conducted promptly without taking a time that would be normally required for filtering
Ando Tomoaki
Kamiya Ryo
Mai Tan V.
Yahama Corporation
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