JPH11202007A - Frequency analyzer - Google Patents

Abstract

(57) [Problem] To provide a frequency analyzer capable of arbitrarily setting a frequency to be measured or displayed. SOLUTION: A frequency analysis device 1 has an audio input unit 2, a microphone 4, and an A for measuring and displaying a signal level of an arbitrary band frequency set by a user.
A / D converter 6, a spectrum analysis unit 8, a control unit 10, an operation unit 12, a display driver 14, and a display unit 16 are provided. When the user operates the operation unit 12 to set the band frequency, the control unit 10 sets each coefficient of the digital filter that realizes each bandpass filter of the spectrum analysis unit 8. If the number of bands for which frequency analysis is performed by the spectrum analyzer 8 exceeds the number of bands that can be displayed on one screen, the bands are displayed on a plurality of screens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency analyzer for measuring and displaying the distribution of frequency components such as audio signals.

[0002]

2. Description of the Related Art A frequency analyzer (spectrum analyzer) measures a frequency component of an input signal for each frequency band (band) and displays the distribution thereof. It can be easily realized by using a dedicated IC in which a set of bandpass filters is used. For example, in a car audio system, a 7-band or 14-band frequency analyzer using a dedicated IC is often used.
By providing a display unit such as a liquid crystal display device, frequency components of each band are displayed.

[0003]

In the above-mentioned conventional frequency analyzer, the frequency components are measured and the number of bands to be displayed is determined in advance, so that the user knows other frequency components. I couldn't do that and felt inconvenient. FIG. 8 is a diagram illustrating an example of a display unit of a conventional frequency analysis device. For example, in the case of a frequency analyzer for measuring frequency components of seven bands, as shown in FIG. 8, the display unit includes seven display bars, but the number of bands to be measured and each frequency are predetermined. Therefore, only a specific frequency component can be displayed on the display unit. Further, these display bars not only have a role of simply displaying the frequency components of each band, but also have a role of visually entertaining the user by changing the display in accordance with the music being played. . Therefore, the user may want to display a band having a large change in display, that is, a band having a large change in frequency component.However, conventionally, a frequency to be measured corresponding to each band is predetermined. The frequency component of the band desired by the user could not be displayed.

[0004] When an acoustic expert analyzes the acoustic characteristics of a vehicle cabin and adjusts an amplifier or the like, 31 bands or 64 bands are used to measure the frequency components of many bands.
Band frequency analyzer is often used, but as the number of bands increases, the display area of the display unit increases,
In addition, since it becomes expensive, it is difficult to use such a multi-band frequency analyzer for a vehicle-mounted audio system in terms of space and cost. For this reason, when analyzing the acoustic characteristics of the cabin, it is necessary to use a multi-band frequency analyzer in addition to the frequency analyzer used for the audio system for the vehicle, which hinders miniaturization and cost reduction. At the same time, the analysis work and the accompanying carry-in work were troublesome.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a frequency analysis apparatus capable of arbitrarily setting a frequency to be measured or displayed. .

[0006]

In order to solve the above-mentioned problems, in the frequency analyzer of the present invention, the center frequency of the band-pass filter is variably set by frequency setting means, and the band component of the band component passing therethrough is set. The signal level is detected by the level detecting means, and is visually displayed by the display means. By using a band-pass filter whose frequency can be changed, the frequency to be displayed can be set arbitrarily. Further, since a plurality of types of frequency components can be displayed in a common display area of the display means, the display area of the display means can be reduced, and the size and cost of the device can be reduced. In particular, by making it possible to arbitrarily set the number of bands of the above-described bandpass filter, it is possible to realize a number of bands suitable for various uses.

If the number of bandpass filters for performing frequency analysis, that is, the number of bands that can be displayed is smaller than the number of bands that can be measured, the display switching means changes the pass center frequency of the bandpass filter to be displayed. By switching, frequency components having a greater number of bands than can be displayed at a time can be measured and displayed. In other words, in order to measure and display frequency components of a large number of bands, a display unit having a small display area can be used, and the size and cost of the device can be reduced.

In particular, it is preferable that the above-mentioned band-pass filter is a digital filter realized by digital processing by a processor (for example, a digital signal processor). A digital filter realized by digital processing allows the number and coefficients of bandpass filters to be set freely within a certain range, so the number of bandpass filters and the center frequency of each pass can be set arbitrarily. Suitable for.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A frequency analyzer according to an embodiment of the present invention is characterized in that a band frequency to be measured or displayed can be set arbitrarily. Hereinafter, a frequency analyzer according to an embodiment will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a frequency analyzer according to an embodiment to which the present invention is applied. The frequency analysis device shown in FIG. 1 extracts an audio band or the like from an audible frequency band of an audio signal or the like and displays a frequency component of each band. It includes an A / D converter 6, a spectrum analysis unit 8, a control unit 10, an operation unit 12, a display driver 14, and a display unit 16.

An audio input unit 2 receives an audio signal from a CD player, an FM / AM tuner, or the like. The microphone 4 is for collecting white noise radiated into the vehicle interior to analyze, for example, acoustic characteristics in the vehicle interior. The A / D converter 6 samples an analog audio signal input through the audio input unit 2 or an analog output of the microphone 4 at a predetermined sampling frequency (for example, 44.1 kHz) and converts the analog audio signal into digital audio data. .

The spectrum analysis unit 8 includes a DSP (Degita
l Signal Processor) has an equivalent plurality of (for example, seven) band-pass filters realized by digital processing.
The spectrum analysis is performed on the digital audio data output from the / D converter 6. The control unit 10 issues an instruction to change the pass band of each band pass filter of the spectrum analysis unit 8 so as to match each band frequency (pass center frequency of each band) arbitrarily set by the user, Control is performed to display on a screen the frequency components of each band analyzed by the spectrum analysis unit 8.

The operating section 12 has a "band setting" key for the user to set the pass center frequency of each band. The pass center frequency is set at a predetermined interval (for example,
20 Hz, 25 Hz, 31.5 Hz, 40 Hz,..., 3 octave intervals), and a method of selecting and setting a plurality of options, or directly inputting and setting the value of the pass center frequency. Various methods such as a method are conceivable. Further, the operation unit 12 includes a “display switching” key for switching the display of the frequency components when the number of pass center frequencies is large and the frequency components of all the bands cannot be displayed at once. The display driver 14 includes the control unit 1
0, and drives the display unit 16 to graphically display the level value of each band.

FIG. 2 is a diagram showing a detailed configuration of the spectrum analyzer 8 shown in FIG. As shown in the figure, the spectrum analysis unit 8 includes a de-emphasis correction unit (DE
P) 20, band-pass filters (BPF) 30-1 to 30-3
0-n, level detectors 40-1 to 40-n, an interface unit 50, and a timing generator 52,
As described above, these are realized by digital processing by the DSP.

The de-emphasis correction section 20 has, for example, 1
The following IIR (Infinite Impulse Response) type digital filter performs de-emphasis correction for removing the influence of noise and distortion on the input digital audio signal. Bandpass filters 30-1 to 30-
n is, for example, a second-order IIR type digital filter, and passes a frequency component near a predetermined frequency set by the user. Level detectors 40-1 to 40-n
Detects the signal level of each output of the band-pass filters 30-1 to 30-n, and outputs the detection result to the interface unit 50.

The interface unit 50 sends an operation instruction and various setting signals sent from the control unit 10 to each component in the spectrum analysis unit 8, or sends a signal to the level detection unit 40-1.
Band-pass filter 30-1 output from .about.40-n
The signal level of each output of the signals 30 to 30-n is output to the control unit 10. The timing generator 52 creates various timing signals for designating the operation timing of each component based on the input external clock signal.

FIG. 3 is a diagram showing the configuration of the band-pass filters 30-1 to 30-n realized by digital processing by the DSP. As shown in the figure, each of the band-pass filters 30-1 to 30-n is, for example, a second-order IIR filter, and includes delay units 61 to 64, a multiplier 7
1 to 74 and an adder 80. By changing the set values of the coefficients An, -An, Bn, and Cn of the four multipliers 71 to 74, the bandpass filter 30
The pass center frequency of -1 to 30-n can be changed and set to an arbitrary value.

The above-described level detectors 40-1 to 40-n
Are the control unit 10, the display driver 14,
The display unit 16 corresponds to a display unit, the control unit 10 corresponds to a frequency setting unit, and the control unit 10 and the display driver 14 correspond to a display switching unit.

The frequency analyzer 1 of the present embodiment has such a configuration, and the operation will be described next. In addition,
In the following description, it is assumed that the display screen of the display unit 16 includes a maximum of seven bands of display bars on one screen.

FIG. 4 is a flowchart showing the operation procedure of the frequency analyzer 1 for displaying the level value of each band set to an arbitrary value, and mainly shows the operation of the control unit 10. When the power of the frequency analysis device 1 is turned on, the control unit 10
It is determined whether the “band setting” key of the operation unit 12 has been pressed by the user (step 100). When the “band setting” key is pressed by the user, the control unit 10 determines whether or not the frequency input operation is performed by the user (step 101) and the operation is determined (step 101). Step 102).

FIG. 5 is a diagram showing an example of the input screen of the band frequency. As shown in the figure, seven display bars 90-1 to 90-7 corresponding to seven bands to be displayed are shown on the frequency input screen. Each display bar 90
Below -1 to 90-7, there are provided frequency input areas 92-1 to 92-7 for inputting respective band frequencies. For example, a horizontal cursor key provided on the operation unit 12 is pressed. Each time, the frequency input area 92-1
Any one of .about.92-7 blinks cyclically. When any one of the frequency input areas 92-1 to 92-7 is in a blinking state, the user presses the numeric keypad of the operation unit 12 so that the band frequency corresponding to the display bar is displayed in the blinking frequency input area. Can be entered directly.

Alternatively, instead of directly inputting the band frequency, the band frequency may be selected from a plurality of candidate values prepared in advance. For example, as described above, when one of the frequency input areas 92-1 to 92-7 is in a blinking state and a vertical cursor key provided on the operation unit 12 is pressed, a plurality of selection candidate values are displayed. A partial selection window screen is displayed. Each candidate value included in the selection window screen is provided with a selection number, and by inputting a selection number corresponding to a candidate value to be selected using a numeric keypad, this candidate value can be input as a band frequency. it can.

The band frequencies need not be set in ascending or descending order along the positions where the display bars 90-1 to 90-7 are arranged, and the same band frequency is set in a plurality of display bars. It may be. Further, it is not necessary to input a band frequency corresponding to all of the seven display bars 90-1 to 90-7 shown in FIG. 5, and a band frequency may be input corresponding to less than seven display bars. It may be.

Further, at the lower right of the frequency input screen shown in FIG. 5, a "confirm" button 94 for confirming the inputted band frequency is displayed. When selected, the control unit 10 determines that the input operation of the band frequency has been determined.

When the input operation of the band frequency by the user is determined, the control unit 10 then transmits the n number of signals to the spectrum analysis unit 8 so that only signals in the vicinity of these input and set band frequencies are passed. Bandpass filter 30
-1 to 30-n, and the number n of the bandpass filters 30-1 and the like,
The coefficients An, -An, Bn, and Cn are set (step 103). For example, in the band frequency input screen shown in FIG. 5, seven frequency input areas 92-1 to 92-7 corresponding to all the seven display bars 90-1 to 90-7.
, The number n of the band-pass filters is 7, and the band-pass filters 30-1 to 30-
7, coefficients An, -An, Bn, and Cn are set.

When the setting of each band frequency is completed in this way, or when the setting processing of the band frequency is not selected (No in step 100).
Immediately after the power is turned on, the control unit 10 sends an instruction to start the frequency analysis operation to the spectrum analysis unit 8, and the signal level of each component of the set band frequency is extracted (step 104). Next, the control unit 10 captures the signal level of each band extracted by the spectrum analysis unit 8 (step 105), and creates image data necessary for displaying the captured signal level of each band, The display driver 14 is controlled to display the signal level of each band on the display unit 16 at that time (step 106).

FIG. 6 is a diagram showing a specific example of a display screen on which signal levels for seven bands set by the user are displayed. The seven display bars show the band frequency 20H set using the band frequency input screen shown in FIG.
z, 40Hz, 200Hz, 1kHz, 4kHz, 8k
Hz and 16 kHz are set, and the signal level of each frequency component included in the audio signal input via the audio input unit 2 is graphically displayed.

Next, the control unit 10 determines whether or not a predetermined time (for example, 50 msec) has elapsed after instructing the spectrum analysis unit 8 to perform the frequency analysis operation in step 104 (step 107). Then, the processing after step 100 is repeated.

As described above, the frequency analyzer 1 of the above-described embodiment can arbitrarily set the number of bands and each band frequency by operating the operation unit 12 by the user. In particular, when each band-pass filter 30-1 in the frequency analysis unit 8 is realized by digital processing by a DSP, the number of bands and each band frequency can be set freely.

In particular, when a band-pass filter is formed by an analog circuit, it is not easy to change the number of bands and the band frequency, and errors due to variations in characteristic values of capacitors and resistors, and a spectrum using a switched capacitor. An error of the CR oscillator in the analysis IC occurs, but when a band-pass filter is realized by digital processing by the DSP, the band-pass filter operates in synchronization with an external clock with a small error supplied from a crystal oscillator or the like. The error of the filter 30 is small, and it is easy to realize a high-order filter with high accuracy.

If the DSP used in another audio device such as a CD player has sufficient processing capability, the function of the spectrum analyzer 8 can be realized using this DSP. There is no need to provide an IC dedicated to analysis, and the number of components can be reduced to reduce cost.

As described above, by using the band-pass filter 30-1 or the like capable of changing the band frequency, a plurality of types of frequency components can be displayed on a common display bar on the display screen. The screen area can be reduced, and the size and cost of the device can be reduced.

By the way, in order to analyze the acoustic characteristics of the cabin, it is necessary to measure the signal levels of many bands. In the frequency analyzer 1 described above, the number of bands can be increased by setting the number n of the band-pass filters 30-1 and the like to a large value. Since the size cannot be made too large, the display screen shown in FIG. 6 cannot be made large according to the number of bands. Therefore, when the number of measurement bands exceeds the number of display bands (= 7), the band frequency to be displayed is switched as shown below,
That is, by switching the display screen, it is possible to realize the display of the signal level of a larger number of bands.

FIG. 7 is a flowchart showing the operation procedure of the frequency analyzer 1 when the number of measurement bands is larger than the number of display bands. When the power of the frequency analyzer 1 is turned on, the control unit 10 causes the user to perform “band setting” on the operation unit 12.
It is determined whether a key has been pressed (step 20).
0). When the “band setting” key is pressed by the user, the control unit 10 determines whether or not a frequency input operation has been performed by the user (step 201) and the operation has been determined (step 201). Step 202).

As shown in FIG. 6, the maximum value of the number of bands that can be displayed on one screen is 7, but by selecting a "display switch" button 96 included in the band frequency input screen shown in FIG. The frequency input band can be switched. By selecting the "display switching" button 96 as appropriate and directly inputting the value of each band frequency, or selecting one of a plurality of candidate values, for example, frequencies for 28 bands are input.

When the input operation of the band frequencies for the 28 bands by the user is determined, the control section 10 sends the spectrum analysis section 8 a signal to the 28 band pass filters 30-1 to 30-1 having the respective band frequencies. Coefficients An, -An, Bn, C
n is set (step 203).

When the setting of the band-pass filters 30-1 for 28 bands is completed in this way, the control unit 10
Sends an instruction to start the frequency analysis operation to the spectrum analyzer 8, and extracts the signal levels of the 28 bands set by the spectrum analyzer 8 (step 204). Further, the control unit 10 captures the signal levels of the extracted 28 bands (step 205),
The image data necessary to display the signal level of each of the captured bands is created for 28 bands (for four screens),
The display driver 14 is controlled to display the signal level of each band at that time for one screen on the display unit 16 (step 206).

Next, the control unit 10 determines whether or not a predetermined time has elapsed after instructing the spectrum analysis unit 8 to perform the frequency analysis operation in step 204 (step 207). Repeat the process. If the predetermined time has not elapsed, the control unit 10 determines whether or not the user has issued a display screen switching instruction (step 208). For example, when the number of measurement bands exceeds seven, a “display switching” button shown in FIG. 5 is displayed on a part of the screen shown in FIG. When the "switch" button is selected, the band selected as the display target is switched for one screen, and the signal levels of seven bands for one screen after this switching are displayed (step 20).
6). In this way, screen switching is performed in order, and 28
The display of each signal level of the band is performed.

As described above, the display screen is appropriately switched according to the user's instruction to display the signal levels for the seven bands included in each screen, thereby analyzing the acoustic characteristics of the vehicle interior and adjusting the amplifier and the like. , The signal levels of many bands that cannot be displayed on one screen can be displayed. In addition, even when displaying multi-band signal levels in this manner, it is not necessary to increase the size of the scene on the display unit 16, and the size and cost of the frequency analysis device 1 can be reduced. .

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, when the frequency components for 28 bands are displayed according to the operation procedure shown in FIG. 7, the user sets each of the band frequencies for 28 bands. The frequency may be fixedly set. That is, it is the same in that multi-band signal levels are switched and displayed, and the multi-band signal levels can be displayed by the frequency analyzer 1 having a narrow display screen. Cost reduction can be realized.

In the above-described embodiment, when setting the band frequency, the numerical value of the frequency is directly input or selected from options. However, the minimum value and the maximum value of the band frequency to be measured are set. Thereby, a band frequency may be automatically set at a predetermined interval between these frequencies. For example, when the band frequency is set every 1/3 octave, the minimum frequency is set to 20H
z, by setting the maximum frequency to 80 Hz, 2
0Hz, 25Hz, 31.5Hz, 40Hz, 50H
z, 63 Hz and 80 Hz are set as band frequencies.

Also, the band frequencies may be automatically and uniformly set by setting the minimum and maximum band frequencies and the number of bands therebetween.

In the above embodiment, the Q (pass band width / pass center frequency) of each band pass filter is not particularly limited. For example, when Q is a constant value for all band pass filters. Also, there is a case where the value of Q is reduced as the band frequency increases. By decreasing the value of Q as the band frequency increases, the pass bandwidth can be kept constant even when the band frequency changes. In particular, by realizing a bandpass filter using a DSP, the value of Q can be set freely.

In the above-described embodiment, when frequency analysis of multiple bands (for example, 28 bands) is performed by the frequency analyzer 1 in order to analyze the acoustic characteristics of the vehicle interior,
It is desirable to emit white noise from a sound source set in the passenger compartment. This white noise is generated by a DSP or the like that implements the spectrum analysis unit 8 and is output from a speaker (not shown). A noise signal may be recorded, and white noise may be generated by a CD player.

[0045]

As described above, according to the present invention, the pass center frequency of the band-pass filter is variably set by the frequency setting means, and the signal level of the band component passing therethrough is detected by the level detecting means. The frequency to be displayed can be set arbitrarily by using a band-pass filter which is visually displayed by the display means and whose frequency can be changed. Further, since a plurality of types of frequency components can be displayed in a common display area, the display area of the display means can be reduced, and the size and cost of the device can be reduced.

When the number of bands that can be displayed is smaller than the number of bands that can be measured, by switching the pass center frequency of the bandpass filter to be displayed, the number of bands that can be displayed at one time is increased. Since the frequency components of the number of bands can be measured and displayed, a display means having a small display area can be used when trying to measure and display the frequency components of a large number of bands. And cost reduction becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a frequency analysis device according to an embodiment to which the present invention is applied.

FIG. 2 is a diagram showing a detailed configuration of a spectrum analyzer shown in FIG.

FIG. 3 is a diagram illustrating a detailed configuration of a bandpass filter illustrated in FIG. 2;

FIG. 4 is a flowchart illustrating an operation procedure of the frequency analysis device that displays a level value of each band set to an arbitrary value.

FIG. 5 is a diagram illustrating an example of a band frequency input screen.

FIG. 6 is a diagram showing an example of a screen on which signal levels for seven bands set by a user are displayed.

FIG. 7 is a flowchart showing an operation procedure of the frequency analysis device when the number of measurement bands is larger than the number of display bands.

FIG. 8 is a diagram showing an example of a display screen of a conventional frequency analyzer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frequency analysis apparatus 2 Audio input part 4 Microphone 6 A / D converter 8 Spectrum analysis part 10 Control part 12 Operation part 14 Display driver 16 Display part 30-1-30-n Bandpass filter 40-1-40-n level Detector 61-64 Delayer 71-74 Multiplier

Claims (5)

[Claims] 1. A pass center frequency can be set, a band pass filter having a predetermined number of bands for extracting a predetermined band component from an input signal, and a signal level of a band component passed through the band pass filter. Level detecting means for detecting, display means having a display area for visually displaying the magnitude of the signal level detected by the level detecting means, and frequency setting means for setting a pass center frequency of the band-pass filter. A frequency analysis device comprising: 2. The frequency analyzer according to claim 1, wherein the number of bands of the band-pass filter can be arbitrarily set, and the number of bands is set by the frequency setting unit. 3. The band according to claim 1, wherein the number of bands of the band-pass filter is set to a value larger than the number of bands that can be displayed at one time by the display unit. A frequency analysis apparatus comprising: a display switching unit that switches a pass center frequency of the bandpass filter to be displayed on the display unit by changing a pass filter. 4. A band-pass filter having a predetermined number of bands for extracting a predetermined band component from an input signal; a level detection unit for detecting a signal level of the band component passed through the band-pass filter; A display unit that has a display area corresponding to the number of bands smaller than the number of bands of the pass filter, and that visually displays the magnitude of the signal level detected by the level detection unit in the display area; And a display switching unit that switches a pass center frequency of the band-pass filter to be displayed on the display unit by changing the band-pass filter corresponding to (b). 5. The frequency analysis device according to claim 1, wherein the band-pass filter is a digital filter realized by digital processing by a processor.