Electrical audio signal processing systems and devices – Sound effects – Reverberators
Reexamination Certificate
1999-11-23
2004-08-24
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Sound effects
Reverberators
C381S061000, C084S629000, C084SDIG002, C708S322000
Reexamination Certificate
active
06782105
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a reflection sound generator for generating reflection sounds of an input sound signal using an FIR (Finite Impulse Response) filter. The reflection sound generator allows a greater number of reflection sounds to be generated from a smaller number of parameters, and the reflection sound generator further makes it easy to set and change reverberation characteristics of a sound field such as room size and liveness.
The reflection sound generator using the FIR filter is a device to carry out convolution operation of an input sound signal based on reflection sound parameters, which determine a sequence of or group of reflection sounds in terms of respective delay times and gains or magnitudes, to produce reflected and reverberated sounds. Such a device is used in various applications, for example, for creating the realism of any sound field space (e.g., a hall space) in a limited space (e.g., small room). It may also be provided in an acoustic feedback system for adjusting reverberation characteristics of a room (e.g., a music listening room) or a hall, or for prolonging a reverberation time.
FIG. 2
shows the most basic structure of a reflection sound generator using a conventional FIR filter. This device is designed to produce reflection sounds through one FIR filter
10
. For the FIR filter
10
, as shown in FIG.
3
(
a
), for example, a set of reflection sound parameters is installed such that a sequence of reflection sounds are generated at proper time intervals while their magnitudes gradually decrease to attenuate with time. The FIR filter
10
carries out the convolution operation of an input sound signal based of the reflection sound parameter set to generate a corresponding reflection sound signal.
The time interval At tuned by the FIR filter
10
can be lengthened or shortened throughout its full time domain, thereby causing a variation of room size. For example, as shown in FIG.
3
(
b
), the time interval At of the FIR filter
10
can be lengthened so that the audience can feel the room to become wider. Gains of the reflection sound parameters can also be changed in proportion to the delay times of the respective reflection sounds while maintaining the time interval At, resulting in a variation of liveness. For example, as shown in FIG.
3
(
c
), each gain can be raised in proportion to each delay time to create a live sound field.
According to the structure of the reflection sound generator of
FIG. 2
, the number of parameters set for the FIR filter
10
is, however, required to correspond to the number of reflection sounds (equivalent to the number of taps of the device) to be generated. To solve this problem, another type of reflection sound generator such as shown in
FIG. 4
has been proposed. In this reflection sound generator, a plurality of FIR filters
12
,
14
,
16
are connected in series while respective outputs of the FIR filters
12
,
14
,
16
are coupled commonly to an adder
17
to generate resultant output sounds. FIGS.
5
(
a
),
5
(
b
) and
5
(
c
) show reflection sound-parameters of the FIR filters
12
,
14
,
16
, respectively. As shown, the first FIR filter
12
generates a top part containing an initial reflection sound. Based on the initial reflection sound part, the second FIR filter
14
generates a reverberant reflection sound part following the initial reflection sound part. Then, based on the reverberant reflection sound part, the third FIR filter
16
generates a further reverberant reflection sound part following the reverberant reflection sound part. In this case, the next-stage reflection sounds are generated based on the previous-stage reflection sounds, so that the density of reflection sounds gradually increases along the time axis, thereby generating a greater number of reflection sounds from a smaller number of parameters.
The structure of the reflection sound generator of
FIG. 4
, having the reflection sound parameters shown in FIGS.
5
(
a
),
5
(
b
) and
5
(
c
), however, raises another problem with respect to setting and changing of reverberation characteristics such as the room size and the liveness. In other words, the setting and changing of reverberation characteristics requires respective parameters to be adjusted for each FIR filter
12
,
14
,
16
, and this adjustment.makes it hard to freely set and change the reverberation characteristics.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems in the conventional technology, and it is an object of the invention to provide a reflection sound generator that allows a greater number of reflection sounds to be generated from a smaller number of parameters, and that further makes it easy to set and change reverberation characteristics such as room size and liveness.
The inventive apparatus is constructed for processing an input sound to generate a sequence of reflection sounds along a time axis including an initial reflection sound and subsequent reverberant reflection sounds. In the inventive apparatus, a first filter of Finite Impulse Response type is provided with a first set of parameters representing a first distribution pattern of reflection sounds. The first distribution pattern has a time length sufficient to cover the initial reflection sound and the subsequent reverberant reflection sounds. Each parameter determines a magnitude (gain) and a delay time of each reflection sound such that the reflection sounds are distributed at intervals along the time axis and such that the magnitudes of the reflection sounds gradually decrease along the time axis. The first filter executes convolution operation of sample data of the input sound by the first set of parameters to generate first data containing a sequence of reflection sounds of the input sound. A second filter of Finite Impulse Response type is provided with a second set of parameters representing a second distribution pattern of additional reflection sounds. The second distribution pattern has a time length shorter than that of the first distribution pattern and longer than each interval of the reflection sounds. Each parameter determines a magnitude and a delay time of each additional reflection sound such that the additional reflection sounds are arranged at intervals shorter than those of the reflection sounds. The second filter executes convolution operation of the first data by the second set of parameters to generate second data containing additional reflection sounds which fill the intervals of the reflection sounds of the input sound.
Preferably, the second filter is provided with the second set of parameters designed such that the magnitudes of the additional reflection sounds gradually decrease along the time axis.
Preferably, the first filter is provided with the first set of parameters designed such that the reflection sounds are distributed at variable intervals, which become gradually short along the time axis.
Preferably, the first filter is provided with the first set of parameters, which can be altered to expand or contract the intervals of the reflection sounds while maintaining relative proportions of the magnitudes thereof so as to change.a rate of attenuation of the reflection sounds along the time axis.
Preferably, the first filter is provided with the first set of parameters, which can be altered to increase or decrease the magnitudes of the reflection sounds in proportion to the delay times of the reflection sounds while maintaining the intervals of the reflection sounds so as to change a rate of attenuation of the reflection sounds along the time axis.
Preferably, the first filter is provided with the first set of parameters, which can be altered so as to periodically fluctuate the delay times of the respective reflection sounds independently from each other along the time axis.
Preferably, the second filter is provided with the second set of parameters, which can be altered so as to periodically fluctuate the delay times of the respective additional reflection sounds independently from each other alo
Sahara Shinichi
Shimizu Yasushi
Grier Laura A.
Isen Forester W.
Pillsbury & Winthrop LLP
Yamaha Corporation
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