JP2010258880

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DESCRIPTION JP2010258880
An object of the present invention is to improve the sound quality at low cost by improving
transient characteristics immediately before an on-vehicle speaker with a small amount of
calculation, and as a result, improve the feeling of sound field. A digital waveform compensation
circuit (12) delays an input signal by a delay time until a distortion component of a first wave at
the time of impulse input obtained by an impulse response measurement result of a vehiclemounted speaker (15). 121, and a low pass filter (LPF 122) that generates a waveform having a
width corresponding to the distortion waveform of the first wave of the delayer output based on
the filter characteristics obtained by the impulse response measurement result, and the output of
the low pass filter The phase inversion circuit 123 generates an opposite phase signal
component that reduces the distortion component of the first wave, and the adder 125 adds the
input signal and the output of the phase inversion circuit. [Selected figure] Figure 2
Digital waveform compensation circuit
[0001]
The present invention relates to a digital waveform compensation circuit suitable for use in an
amplifier to which an on-vehicle speaker is connected.
[0002]
In-vehicle speakers used in the vehicle interior acoustic space have distortion response
waveforms that are less responsive than an ideal sound waveform due to insufficient strength of
vehicle structures such as iron plates and interior materials used as enclosures around the
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1
speakers It is known that many components (undershoot and overshoot) occur.
This distortion component waveform is an unnecessary component not included in the original
waveform, and is one of the causes that adversely affect the sound quality.
[0003]
For this reason, although improvement tendency is seen by securing the strength of the vehicle
structure etc., complete measures are difficult, and cost for that purpose was required. In
addition, in order to secure the strength, the weight increase is caused, the adverse effect on the
fuel efficiency is considered, and sufficient measures can not be taken. Therefore, measures have
conventionally been taken on the amplifier side to which the in-vehicle speaker is connected. For
example, distortion component waveform reduction processing is performed by convolution
operation of an impulse response using an adaptive filter (FIR: Finite Impulse Response) It had
been.
[0004]
On the other hand, conventionally, with regard to the non-uniformity of the frequency
characteristic at the viewing point due to the interference between the direct sound from the
speaker and the reflected sound from the wall etc., the frequency of the reflected sound
intervened between the delay means and the level adjustment means A sound field correction
device has been proposed that compensates with a low pass filter (LPF) whose filter
characteristics are determined based on the characteristics (see, for example, Patent Document
1).
[0005]
Japanese Patent Application Laid-Open No. 60-193776
[0006]
However, according to the reduction processing of the distortion component waveform by the
convolution operation using the above-mentioned adaptive filter, a huge amount of operation is
required, resulting in an increase in cost.
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Further, the technology disclosed in Patent Document 1 relates to sound field correction for
interference between direct sound and reflected sound, and is not sound field correction for
direct sound on the front surface of a speaker.
[0007]
The present invention has been made to solve the above-mentioned problems, and the transient
characteristics immediately before a vehicle-mounted speaker are improved with a small amount
of calculation to improve the sound quality at a low cost, and as a result, the feeling of sound
field is improved. It is an object of the present invention to provide a digital waveform
compensation circuit that can
[0008]
In order to solve the above-mentioned problems, the digital waveform compensation circuit of
the present invention has an input signal corresponding to the delay time until the distortion
component of the first wave at the time of impulse input obtained by the impulse response
measurement result of the on-vehicle speaker A low-pass filter for generating a waveform having
a width corresponding to the distortion waveform of the first wave of the delayer output based
on the delay characteristic delayed by just a second delay, the filter characteristic obtained by the
impulse response measurement result, A phase inverting circuit that generates an antiphase
signal component that reduces the distortion component of the first wave from the output of a
band pass filter, and an adder that adds the input signal and the output of the phase inverting
circuit It is.
[0009]
According to the digital waveform compensation circuit of the present invention, it is possible to
improve the sound quality at low cost by improving the transient characteristics immediately
before the on-vehicle speaker with a small amount of calculation, and as a result, it is possible to
improve the feeling of sound field.
[0010]
It is a figure which shows the structural example of the vehicle-mounted acoustic equipment in
which the digital waveform compensation circuit which concerns on Embodiment 1 of this
invention is used.
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It is the figure which showed the internal structure of the digital waveform compensation circuit
which concerns on Embodiment 1 of this invention with an equivalent circuit.
FIG. 5 is a diagram schematically showing the operation of the digital waveform compensation
circuit according to the first embodiment of the present invention.
It is the figure which showed the internal structure of the digital waveform compensation circuit
which concerns on Embodiment 2 of this invention with an equivalent circuit.
It is the figure which showed the internal structure of the digital waveform compensation circuit
which concerns on Embodiment 3 of this invention with an equivalent circuit. It is the figure
which showed the frequency characteristic by the digital waveform compensation circuit based
on Embodiment 1 of this invention in comparison with a prior art example.
[0011]
Hereinafter, a digital waveform compensation circuit according to an embodiment of the present
invention will be described in detail with reference to the drawings. Embodiment 1 FIG. 1 is a
diagram showing a configuration example of an on-vehicle acoustic device in which a digital
waveform compensation circuit according to a first embodiment of the present invention is used.
[0012]
As shown in FIG. 1, the in-vehicle audio device 1 includes an ADC (Analog Digital Converter) 11, a
digital waveform compensation circuit 12 according to the first embodiment of the present
invention, a DAC (Digital Analog Converter) 13, and a power amplifier. 14 and an on-vehicle
speaker 15.
[0013]
The ADC 11 converts an analog input audio signal into a digital audio signal and outputs the
digital audio signal to the digital waveform compensation circuit 12.
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As described later, the digital waveform compensation circuit 12 generates the first sound
(overshoot / undershoot) at the time of impulse input obtained from the impulse response
measurement result of the in-vehicle speaker 15 in advance of the digital audio signal output
from the ADC 11 The delay output is delayed by a delay time until a distortion component
occurs, and this delay output is also formed into a waveform having a width corresponding to the
distortion waveform of the first wave of the delay output based on the filter characteristics
obtained by the impulse response measurement result. Further, the signal component of the
opposite phase for reducing the distortion component of the first wave is generated, added to the
input digital audio signal, and output to the DAC 13. Details will be described later.
[0014]
The DAC 13 converts the digital audio signal output from the digital waveform compensation
circuit 12 into an analog audio signal and outputs the analog audio signal to the power amplifier
14. The power amplifier 14 amplifies the analog audio signal output by the DAC 13 and outputs
the amplified signal to the on-vehicle speaker 15 which is an electroacoustic transducer.
[0015]
Here, each of the ADC 11, the digital waveform compensation circuit 12, and the DAC 13 is
implemented by being implemented in the digital signal processing device 10 (DSP) and
subjected to signal processing in the DSP 10. Details will be described later.
[0016]
FIG. 2 is a diagram showing an internal configuration of the digital waveform compensation
circuit 12 according to the first embodiment of the present invention as an equivalent circuit.
The digital waveform compensation circuit 12 is composed of an IIR (Infinite Impulse Response)
filter having an impulse response function that returns a nonzero value at infinite time, and a
delay unit (Delay) 121 and a low pass filter 122 (hereinafter referred to as LPF 122). , A phase
inverting circuit 123, a level adjusting circuit 124, and an adder 125.
[0017]
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The delay unit 121, delay time until the distortion waveform component of the first wave related
to the overshoot and undershoot at the time of impulse input obtained by the impulse signal
measurement result of the in-vehicle speaker 15 and the input signal (INPUT) The signal is
delayed by (td) and output to the LPF 122.
[0018]
The LPF 122 generates a waveform having a width corresponding to the distortion waveform of
the first wave at the output of the delay device 121 based on the filter characteristic obtained by
the impulse response measurement result in advance, and outputs the waveform to the phase
inversion circuit 123.
The phase inversion circuit 123 generates, from the output of the LPF 122, a signal component
of the opposite phase for reducing the distortion component of the first wave, and outputs the
signal component to the adder 125.
[0019]
The adder 125 adds the signal obtained by adjusting the level of the input signal (INPUT) by the
level adjustment circuit 124 and the output of the phase inversion circuit 123 described above,
and outputs the result as an OUTPUT signal to the power amplifier 14.
[0020]
FIG. 3 is a diagram schematically showing the operation of the digital waveform compensation
circuit 12 according to the first embodiment of the present invention.
The operation of the digital waveform compensation circuit 12 according to the first embodiment
of the present invention shown in FIG. 1 and FIG. 2 will be described below with reference to FIG.
[0021]
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As described above, in the on-vehicle speaker 15, distortion waveforms of overshoot and
undershoot with poor transient response occur with respect to the input sound signal. Here,
waveform compensation in the digital domain is performed in order to cancel out this distortion
waveform component. Therefore, the in-vehicle speaker 15 is installed in the vehicle
compartment in advance, the impulse response waveform on the front surface of the in-vehicle
speaker 15 is measured (a), and attention is paid to distortion waveform components generated
after fundamental wave driving. It is necessary to set in advance in DSP 10 (digital waveform
compensation circuit 12) parameters including delay time and filter characteristics for simulating
the distortion component of the first wave for the shoot.
[0022]
After the above-described preparation processing, the digital waveform compensation circuit 12
delays the signal branched from the input signal (INPUT) by the time td according to the
parameter set by the delay unit 121 and passes it through the LPF 122 and the LPF 122 A
waveform corresponding to the width of the distortion waveform component is generated and
output to the phase inversion circuit 123.
[0023]
The phase inversion circuit 123 generates a signal (distortion compensated waveform) having an
opposite phase to the distortion waveform of the first wave by the output of the LPF 122 (b), and
the adder 125 adjusts the input signal (INPUT) by the level adjustment circuit 124. Is added to
the level-converted signal to cancel the distorted waveform (c), and the distortion component is
reduced by outputting to the power amplifier 14.
[0024]
Here, td is the delay time until the distortion component of the first wave is generated at the time
of impulse input which is obtained by the impulse response measurement result of the in-vehicle
speaker 15 performed in advance, and the filter characteristic is also the same in advance. This
refers to a parameter for generating a waveform having a width corresponding to the distortion
waveform of the first wave obtained by the impulse response measurement result of the onvehicle speaker 15 performed.
[0025]
According to the digital waveform compensation circuit according to the first embodiment of the
present invention described above, only the delay time up to the occurrence of the distortion
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component of the first wave at the time of impulse input obtained by the impulse response
measurement result of the on-vehicle speaker 15 The delayed output is used to generate a
distortion waveform component having a width corresponding to the distortion waveform based
on the filter characteristic similarly obtained by the impulse response measurement result, and
generates an antiphase signal component that reduces the distortion component of the first
wave. Digital waveform compensation is realized by adding and outputting the input digital audio
signal, and the sound quality can be improved.
Further, by configuring the above-described digital waveform compensation circuit 12 with an
IIR filter and processing the signal by the DSP 10, the amount of calculation is small, and the
sound quality is improved inexpensively, and as a result, the sound field feeling of the on-vehicle
speaker 15 is obtained. It can be improved.
[0026]
Second Embodiment
FIG. 4 is a diagram showing an internal configuration of a digital waveform compensation circuit
according to a second embodiment of the present invention as an equivalent circuit.
[0027]
As shown in FIG. 4, in the digital waveform compensation circuit according to the second
embodiment of the present invention, the digital waveform compensation circuit 12 according to
the first embodiment of the present invention shown in FIG. On the other hand, more effective
waveform compensation can be performed by performing a plurality of digital waveform
compensations including the second wave.
Here, a second-order IIR filter is shown. Therefore, the sound quality is improved, and as a result,
the sound field feeling of the in-vehicle speaker 15 can be improved. Further, by processing the
respective digital waveform compensation circuits 12 connected in parallel by the DSP 10, the
amount of calculation is small, and the sound quality can be improved inexpensively.
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[0028]
Also in the second embodiment described above, the impulse response waveform on the front
surface of the in-vehicle speaker 15 installed in the vehicle compartment is measured in advance
as in the first embodiment, and the distortion component is detected in the DSP 10 (digital
waveform compensation circuit 12). It is essential to set parameters related to delay time and
filter characteristics to simulate.
[0029]
Third Embodiment
FIG. 5 is a diagram showing an internal configuration of a digital waveform compensation circuit
according to Embodiment 3 of the present invention as an equivalent circuit.
[0030]
As shown in FIG. 5, in the digital waveform compensation circuit according to the third
embodiment of the present invention, the digital waveform compensation circuit 12 according to
the first embodiment of the present invention shown in FIG. In the second embodiment described
above, the impulse response is also added / subtracted by connecting the digital waveform
compensation circuits 12 in parallel, but as shown in the third embodiment, when the digital
waveform compensation circuits 12 are slave-connected, The convolution of each of the cascaded
digital waveform compensation circuits 12 makes it possible to perform waveform compensation
with higher effect.
[0031]
Therefore, according to the digital waveform compensation circuit according to the third
embodiment, the sound quality can be improved, and as a result, the sound field feeling of the onvehicle speaker 15 can be improved. Further, by performing signal processing of the dependently
connected digital waveform compensation circuit 12 with the DSP 10, more effective waveform
compensation is performed, the amount of calculation is small, and the sound quality can be
improved inexpensively.
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[0032]
Also in the third embodiment described above, as in the first and second embodiments, the
impulse response waveform on the front surface of the in-vehicle speaker 15 installed in the
vehicle compartment is measured in advance, and the DSP 10 (digital waveform compensation
circuit 12) It is essential to set parameters related to delay time and filter characteristics to
simulate distortion components.
[0033]
FIG. 6 is a diagram showing the frequency characteristics of the digital waveform compensation
circuit 12 according to the first embodiment of the present invention described above in
comparison with a conventional example.
6 (a) shows a conventional example, and FIG. 6 (b) shows a response waveform of the digital
waveform compensation circuit 12 according to the first embodiment of the present invention
immediately before the on-vehicle speaker 15 and is shown in FIG. Thus, it can be seen that the
overshoot and undershoot first wave distortion components are reduced. Here, a value set as a
parameter in the DSP 10 (digital waveform compensation circuit 12) exemplifies a case where
the delay time (td) of the delay unit 121 is 0.15 ms and the cutoff frequency (fc) of the LPF 122
is 800 Hz. There is.
[0034]
As described above, according to the digital waveform compensation circuit according to the first
to third embodiments of the present invention, the transient characteristic immediately before
the on-vehicle speaker is improved with a small amount of calculation to improve the sound
quality inexpensively. As a result, the feeling of the sound field can be improved.
[0035]
The functions of the digital waveform compensation circuit 12 shown in FIG. 2, FIG. 4 and FIG. 5
may all be realized by software by the DSP 10, or at least a part of them may be realized by
hardware.
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For example, the digital waveform compensation circuit 12 delays the input signal by a delay
time until the distortion component of the first wave at the time of impulse input obtained by the
impulse response measurement result of the on-vehicle speaker 15 is generated, thereby
measuring impulse response. Based on the filter characteristics obtained as a result, the
distortion waveform of the first wave is generated, the signal component of the reverse phase is
generated to reduce the distortion component of the first wave, and the data processing of
adding to the input signal is one or more. The program may be realized on a computer, and at
least a part of the program may be realized in hardware.
[0036]
Reference Signs List 1 in-vehicle audio device, 10 DSP, 11 ADC, 12 digital waveform
compensation circuit, 13 DAC, 14 power amplifier, 15 in-vehicle speaker, 121 delay unit, 122
low pass filter (LPF), 123 phase inverting circuit, 124 level adjustment Circuit, 125 adders.
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