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JPH09331223

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Notice
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DESCRIPTION JPH09331223
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
signal processing apparatus capable of simply and variously changing an input signal,
particularly an audio signal.
[0002]
Related Background Art If the frequency characteristic in the reproduction environment of an
audio signal is not flat, a graphic equalizer is used to correct this. Generally, this type of graphic
equalizer is configured to divide an input audio signal into a plurality of bands, adjust the signal
level for each frequency band, and synthesize and output the result. In addition, so-called sound
coloring is also performed by increasing or decreasing the signal level in a specific band by
utilizing this property in reverse.
[0003]
On the other hand, in a car audio apparatus, it is difficult to hear a small level reproduction
sound due to an engine sound or wind noise, so that the output signal level is varied according to
the input signal level. This process gives a large gain to a small level signal and reduces the gain
for a large level signal to give its input / output characteristic a compression characteristic, and is
called compression (compression).
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[0004]
Incidentally, this compression process is performed in an analog manner by utilizing the square
characteristic of the semiconductor or in a digital manner by using a digital signal processor
(DSP). However, although the above-mentioned analog method has the advantage that the
amount of compression can be varied continuously, the deterioration of the sound quality
characteristics is generally remarkable, and the compression characteristics are influenced by the
device characteristics of the semiconductor. In the digital system, although the calculation
process is generally very complicated, basically, there is an advantage that the deterioration of
the frequency characteristic (sound quality) of the reproduction signal does not occur.
[0005]
SUMMARY OF THE INVENTION The gain adjustment processing of each band by the graphic
equalizer described above and the compression processing (compress) by the compressor are
very effective in changing the output characteristics of the audio signal and performing so-called
sound creation. Play a big role. However, each of these signal processing functions is
independent of each other, and it is generally the case that the combination thereof is hardly
considered.
[0006]
The present invention has been made in consideration of such circumstances, and an object
thereof is to provide a signal processing device which enables simple, effective, and more diverse
signal processing.
[0007]
SUMMARY OF THE INVENTION In order to achieve the above object, a signal processing
apparatus according to the present invention divides an input signal into a plurality of bands
using a band pass filter, and for each divided band signal The compression processing is
performed using the compression circuit, and after setting the levels of the compressed
processing of each band to be variable, these are combined and output, and the compression
characteristics by each of the above compression circuits are divided into each band. It is
characterized in that it can be set variably for each time.
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[0008]
In other words, by variably setting the compression characteristics to be given to the signals of
each band as well as variably setting the levels of the signals of a plurality of divided frequency
bands, it is possible to obtain a reproduction signal subjected to a variety of adjustments. It is
characterized by having done.
[0009]
Further, according to the invention as set forth in claim 2, particularly, the compression circuit
used for the compression processing in each of the above-mentioned bands becomes y = a {1-1
(1- [x]) n} with respect to the input signal x It is characterized in that it is realized by a digital
signal processor which obtains an output signal y by performing an operation.
Where [x] is the absolute value of signal x, n is the order that defines the compression
characteristics, and a is a coefficient that takes a value such that <1> when x ≧ 0 and <−1>
when x <0. is there.
[0010]
DESCRIPTION OF THE PREFERRED EMBODIMENT A signal processing apparatus according to an
embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a signal processing apparatus
realized as a graphic equalizer having a compress function, and 1a, 1b,... 1n are band pass filters
(BPFs) for dividing an input signal IN into plural frequency bands. ).
Specifically, the input audio signal having a frequency band of 20 Hz to 20 kHz is equally divided
into 5 or 9 frequency bands by these band pass filters 1a, 1b, to 1n. The number of frequency
bands to be divided may be determined according to the specification.
[0011]
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The digital signal processors (DSPs) 2a, 2b,... 2n provided at the output stages of the respective
band pass filters 1a, 1b,... 1n are, for example, configured as shown in FIG. The compression
processing is performed on the signals of the band under individually set compression
characteristics. The compression process will be described later. The variable gain amplifiers
(VGA) 3a, 3b,... 3n are for individually variably setting the gains for the signals subjected to the
compression processing in each of the above-mentioned bands. Are synthesized via the
synthesizer (ADD) 4 and output as the signal OUT of the original frequency band.
[0012]
Now, as shown in FIG. 2, the digital signal processor 2 includes a positive / negative
determination unit 11, a coefficient conversion processing unit 12, an absolute value processing
unit 13, a first subtraction unit 14, a power multiplication processing unit 15, a second
subtraction unit 16, A multiplication processing unit 17 is provided. Then, the input signal x is
subjected to an operation of y = a {1-1 (1- [x]) n} to obtain an compressed output signal y. In the
above equation, for convenience, the absolute value symbol is shown as []. Accordingly, [x]
indicates the absolute value of the signal x. Also, n is an order that defines the compression
characteristics, and is variably set according to the compression characteristics to be set. Further,
a is a coefficient set according to the polarity of the input signal x, and is set as a value <1> when
xx0 and <−1> when x <0.
[0013]
Specifically, the positive / negative determination unit 11 determines whether the positive /
negative of the input signal x in the divided frequency band is, for example, <x ≧ 0, and the
coefficient processing unit 12 determines the result The value of the coefficient a is set according
to. That is, as described above, when the input signal x is <x ≧ 0>, the coefficient processing unit
12 sets the value of the coefficient a as <1>, and when <x <0> The value is set as <-1>. The value
of the coefficient a is given to the multiplication processing unit 17 as polarity information for
the output signal y.
[0014]
On the other hand, the absolute value processing unit 13 obtains the absolute value of the
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amplitude (level) of the input signal x as [x]. The first subtraction processing unit 14 subtracts
the absolute value [x] from the constant <1> to obtain a complement when the maximum
amplitude value of the input signal x is normalized as <1>. According to the complement <1- [x]>,
the attenuation amount according to the level of the input signal x is given logarithmically, and
the power processing unit 15 sets the compression characteristic to set the compression
characteristic according to the signal level. The above-mentioned complement <1- [x]> is
subjected to exponentiation according to n. Specifically, when the order n is <2>, an
exponentiation process of <1- [x]> × <1- [x]> = <1- [x]> 2 is performed, and the order n is In the
case of <3>, <1- [x]> × <1- [x]> × <1- [x]> = <1- [x]> 3 is to be multiplied by a power of n, and
the order n When <4>, <1- [x]> × <1- [x]> × <1- [x]> × <1- [x]> = <1- [x]> 4 As you are
performing exponentiation. That is, the attenuation process to be applied to the input signal x is
obtained according to the signal level by this power process. The inverse compression
characteristic is set such that the higher the signal level, the smaller the amount of attenuation,
and the lower the signal level, the larger the amount of attenuation.
[0015]
The second subtraction processing unit 16 sets an attenuation amount to be actually applied to
the input signal x by subtracting the attenuation amount obtained as described above from the
normalized value <1>. It is. The compression characteristic as shown in FIG. 3 is set such that the
attenuation amount is larger as the level of the input signal x is higher by this subtraction
processing, and the attenuation amount is smaller as the signal level is lower, depending on the
level of the input signal x. A varied signal is obtained as 1- <1- [x]> n. The signal output from the
second subtraction processing unit 16 is led to the multiplication processing unit 17, multiplied
by the above-described coefficient a, converted into an output signal y of a polarity
corresponding to the polarity of the input signal x, and output. .
[0016]
Thus, according to the DSP 2 that executes the above-mentioned signal processing, it is possible
to compress the input signal x under a compression characteristic defined by the order n by
simple processing, that is, without requiring division processing. . That is, the input signal x can
be compressed according to the signal level.
[0017]
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Therefore, according to the present apparatus, the signal divided into a plurality of frequency
bands is subjected to compression processing for each band, the gain for the signal is variably set
thereon, and this is synthesized and output. Since the output characteristics of the signal
components in the band can be set individually, it is possible to variably set the overall gain, in
particular, variably setting the compression characteristics. Therefore, it is possible to easily
perform special signal correction such as, for example, increasing a change in signal level in
another frequency band while making the signal level in a specific frequency band substantially
constant. In other words, it is possible to change the compression characteristics in each band
individually while making use of the function as graphic equalizer, and obtain an output signal
that is color-matched (integer tone change) that matches the playback environment of the audio
signal. It becomes.
[0018]
The present invention is not limited to the embodiment described above. For example, all
functions shown in FIG. 1 can be realized by a DSP, and conversely, a log amplifier (log amplifier;
Log-Amp. It is also possible to set the compression characteristic of each frequency band using.
Further, when the apparatus is actually configured, it is of course possible to appropriately
provide a bypass circuit for the DSP 2 and the VGA 3. Furthermore, after setting the gain for each
signal of the divided frequency band variably, it is also possible to apply compression processing
to this. In short, the present invention can be implemented with various modifications without
departing from the scope of the invention.
[0019]
As described above, according to the present invention, compression processing is applied to
each signal divided into a plurality of bands, and after the gain is variably set, the signals of each
band are combined and output. Therefore, it is possible to give different compression
characteristics to each band while fully utilizing the function as a graphic equalizer, so that it is
possible to give a signal change that could not be expected up to now, and various signal
reproductions Is possible. In particular, special coloring can be applied to the audio signal, and
the configuration of the device itself is simple, and effects such as a large signal processing effect
can be achieved.
[0020]
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Brief description of the drawings
[0021]
1 is a block diagram showing a schematic configuration of a signal processing apparatus
according to an embodiment of the present invention.
[0022]
2 is a diagram showing an example of the configuration of a compression circuit by the digital
signal processor used in the signal processing apparatus shown in FIG.
[0023]
3 is a diagram showing an example of the compression characteristics of the compression circuit
shown in FIG.
[0024]
Explanation of sign
[0025]
1a, 1b,... 1n Bandpass filters (BPF) 2a, 2b,... 2n Digital signal processor (DSP; compress circuit) 3a,
3b,... 3n Variable gain amplifier (VGA) 4 Synthesizer 11 Positive / negative judgment unit 12
coefficient Processing unit 13 absolute value processing unit 14 first subtraction unit 15
exponentiation processing unit 16 second subtraction unit 17 multiplication processing unit
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