Electrical audio signal processing systems and devices – Including frequency control
Reexamination Certificate
1997-09-23
2002-06-18
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Including frequency control
C381S096000
Reexamination Certificate
active
06408079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distortion removal apparatus for removing a harmonic distortion and an intermodulation distortion generated in a system such as a loudspeaker for reproducing, for example, an audio signal and performing high fidelity reproduction of an input signal, a method for determining a coefficient for the distortion removal apparatus. The present invention also relates to a processing speaker system, a multi-processor and an amplifier including the distortion moving apparatus
2. Description of the Related Art
As is well known, in order to reproduce music or announcement in a large space such as concert halls, outside theaters and stadiums, a large-size professional-use loudspeaker system for reproducing a large volume of sound is generally used. Specifically in order to reproduce sound in a high frequency range, a horn loudspeaker is used; and in order to reproduce sound in a low frequency range, a loudspeaker such as woofer or subwoofer is used.
A horn loudspeaker system includes a compression driver, which is an electro-acoustic transducer, and a horn into which sound wave output from the compression driver is input. The compression driver converts the input electric signal into sound wave and outputs the sound wave to the horn, and the horn radiates the sound wave into a large space. In the compression driver, the sound pressure radiated by a diaphragm for generating the sound wave by reducing the diameter of a part at which the compression driver is connected to the horn (a throat section of the horn) rather than the diameter of the diaphragm. Thus, reproduction of a large volume of sound is realized.
However, in such a compression driver, reproduction is distorted by high compression of the air and the distortion is added to the original sound wave. This is one of the causes of the distortion generated when a large volume of sound is reproduced by the horn loudspeaker system, which is quite serious.
In the case of reproduction of sound in a low frequency range in a large volume using a woofer, the diaphragm of the woofer is vibrated to a large amplitude. In this case, the reproduced sound accompanies a distortion due to the kinetic nonlinearity of the dumper or the edge supporting the diaphragm or the nonlinearity of the volume of the air eliminated by the edge.
The above-described distortions are nonlinear distortions referred to as the harmonic distortion and the intermodulation distortion. Such distortions, which are generated due to the above-described reasons when sound is generated in a large volume, deteriorate the sound quality.
A method for removing a distortion generated in a loudspeaker or the like which generates a nonlinear distortion (hereinafter, referred to as a “system”) uses a nonlinear filter. One known nonlinear filter used for such general systems is a Volterra filter. The Volterra filter refers to connecting a one-dimensional filter, a two-dimensional filter, . . . an n-dimensional filter in parallel, performing a convolution operation of an input signal with respect to each filter, and then adding and outputting the results.
Such a method has a problem in that the amount of operation increases to an excessive degree as the number of dimensions increases from a two-dimensional filter to a three-dimensional filter and to an n-dimensional filter. For example, even in the case of removing only a two-order distortion from a loudspeaker as a system, a large-scale apparatus is required to perform a real-time two-dimensional convolution operation of an input audio signal.
The U.S. Pat. No. 4,709,391 to Kaizer at al. entitled “Arrangement for converting an electric signal into an acoustic signal or vice versa and a non-linear network for use in the arrangement” (assigned to U.S. Philips Corporation) and the European Patent application No. 0 168 078 A1 filed in the names of the same inventors propose a nonlinear circuit for correcting a nonlinear distortion referred to as a two-order distortion or a three-order distortion of an electro-acoustic transducer. The method described in these documents is as follows. The nonlinearities of the magnetic flux density of the magnetic circuit of the loudspeaker, inductance of the voice coil, and spring constant of the damper are modelled by an equivalent circuit of an electric circuit to obtain respective constants. Then, the input and output characteristic of the loudspeaker is modelled by a series referred to as the Volterra series in which a usual transfer characteristic is connected in parallel to a nonlinear distortion characteristic. A nonlinear filter for providing an equivalent effect as that by the Volterra filter is connected as a distortion correction circuit to the stage prior to the loudspeaker. By the nonlinear filter, a distortion compensation signal for compensating for the distortion generated by the loudspeaker is added to the audio signal, and the resultant signal is sent to the loudspeaker.
By this method, a distortion removing effect which is equivalent to the effect obtained by two-dimensional and three-dimensional convolution operations is effected without performing such convolution operations.
However, this method requires a significant amount of trouble in order to measure constants for determining the nonlinear transfer characteristic of the loudspeaker, such as the magnetic flux density, inductance and spring constant. Moreover, when any of the measurement results includes a relatively large error and thus a satisfactory effect is not obtained by the above-described procedure, it is difficult to identify which of the constants includes an error. Thus, this method requires significant experience of the operator.
When this method is used for a system from which a nonlinear distortion is to be removed in order to, for example, remove a distortion from a dynamic electric loudspeaker, in the case where the factor of the distortion is clear, it is possible to design a distortion correction circuit. In the case where the distortion generation cannot be modelled by an equivalent circuit, such as in the case of a general system, it is impossible to design a distortion correction circuit.
The U.S. Pat. No. 5,438,625 to W. Klippel entitled “Arrangement to correct the linear and nonlinear transfer behavior or electro-acoustical transducers” (assigned to JBL Incorporated) and the German Patent No. DE 41 11 884 C2 (granted to the same inventor) propose a nonlinear circuit for removing a nonlinear distortion in an electro-acoustic transducer and a method for automatically updating the coefficient for the circuit. According to the method described in these documents, as the method proposed by Kaizer et al., some factors of generation of a nonlinear distortion in the loudspeaker are formulated and a nonlinear circuit to be used as an inverse system is designed. This method is based on the concept of the Volterra filter, but constructs a distortion removing circuit not as a circuit for performing a two- or higher dimensional convolution operation but as a nonlinear circuit for providing the same effect as obtained by the convolution operation.
This method also requires formulation of some factors of the generation of distortion in the loudspeaker as a system in order to design a distortion removing circuit. Such a method is only usable for a system, the mechanism of generation of a distortion of which is clear. Moreover, it is necessary to measure the constants of the expressions after the formulation, which is quite complicated.
The two methods described in the above-described documents require formulation of the mechanism of generation of the distortion in a system in order to remove a distortion therefrom. Accordingly, when the factors of the distortion are not clearly known or when formulation cannot be performed with high precision, these methods cannot be used.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a distortion removal apparatus connected between a signal source and a signal input section of a dist
Katayama Taro
Serikawa Mitsuhiko
Harvey Minsun Oh
Matsushita Electric - Industrial Co., Ltd.
Renner Otto Boisselle & Sklar
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