JPH04301935A - Acoustic equipment for vehicle - Google Patents

Abstract

PURPOSE:To exactly measure an S/N without-being affected by the fluctuation of receiving electric field strength or the fluctuation of the modulation level of received radio waves. CONSTITUTION:At the acoustic equipment for vehicle equipped with a voice reproducing means 9 connected through voice output forming means 7 and 8 to an intermediate frequency band amplifying means 6, a received signal level detecting means 10 is provided to detected the level of a signal received at the intermediate frequency amplifying means 6, a noise level detecting means 13 is provided to detect the noise level of a voice signal at the voice reproducing means, and a storing means 15 is provided to store correlative relation between the detected value of the received signal level detecting means and the peak value of the voice signal level in the case of receiving a prescribed reference signal. Further, a calculating means 14 is provided to calculate the peak value of the voice signal level corresponding to the received signal level and to calculate the S/N according to the calculated peak value and the detected value of the noise level detecting means based on the detected value of the received signal level detecting means and the correlative relation stored in the storing means in the case of receiving broadcasted radio waves by a receiving means.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention measures the S/N ratio when receiving and reproducing broadcast waves while driving.
The present invention relates to a vehicle acoustic device that allows more accurate evaluation of sensitivity during actual driving.

0002

[Prior Art] Various efforts have been made to improve the noise characteristics of vehicle audio equipment. For example, in Japanese Patent Laid-Open No. 62-279719, the output from an AGC detector in a vehicle-mounted radio receiver has been proposed. A system has been proposed in which noise is reduced and sensitivity is improved by controlling the gain of an intermediate frequency amplifier according to the AGC voltage applied.

[0003] By the way, when evaluating the sensitivity of the antenna or the on-vehicle tuner system including the antenna in a vehicle audio device equipped with an antenna and a tuner for receiving broadcast waves such as radio broadcasts, a convenient method is used. As a method, evaluation is performed using the antenna induced voltage or the signal level at the intermediate frequency amplification stage of the tuner system, that is, the voltage value (S meter voltage) of a signal meter (S meter) that can display the signal level as a DC voltage value. method is known.

However, the conventional method described above evaluates the maximum sensitivity of the receiving system during actual driving by measuring only the received signal level without measuring the noise level. This is far from the practical sensitivity, which is affected by the level.

That is, as is well known, when a receiving system of an in-vehicle audio device receives broadcast radio waves from a broadcast station while a vehicle is running, the received electric field strength generally varies depending on changes in the reception environment due to the movement of the vehicle, etc. It varies depending on. Further, the received signal level and generated noise level of the receiving system change according to their own characteristics in accordance with fluctuations in received field strength when receiving broadcast waves. In other words, the received signal level decreases when the received electric field strength decreases below a predetermined value, while the noise level decreases according to the decrease.
When the received electric field strength decreases below a predetermined value, it increases in accordance with the decrease. Therefore, if only the antenna induced voltage or S-meter voltage is measured, it is not possible to evaluate the effect of noise increase when the received field strength decreases, and the practical sensitivity of the receiving system during actual operation cannot be evaluated. There was a problem that it was not possible to evaluate properly.

On the other hand, as a method for evaluating the sensitivity of a broadcast wave receiving system, the ratio of the output signal level of the system at the time of reception to the signal level of the noise component contained in the signal (so-called S/N ratio) is used. The evaluation method is generally well known and is useful as a method for evaluating practical sensitivity including the influence of noise level. This S/N ratio is calculated by measuring the output signal level and the noise level when the receiving system receives a radio wave with a predetermined standard modulation level (for example, 100% modulation or 30% modulation), and calculates the ratio between the two. It is calculated and displayed as a value indicating the sensitivity characteristics of the receiving system.

[0007]

However, while the vehicle is running, the received electric field strength fluctuates as the vehicle moves as described above, and the received signal level and noise level also fluctuate. Further, the modulation level of broadcast radio waves from a broadcast station is different from the above-mentioned reference modulation level, and is not constant but constantly fluctuates. Therefore, without being affected by these
Accurately measure the above output signal level and noise level,
Conventionally, it has been difficult to calculate the S/N ratio.

[0008] The present invention was made in view of the above-mentioned problems, and it is possible to accurately measure the S/N ratio without being affected by fluctuations in received electric field strength or modulation level of received radio waves. The purpose of the present invention is to provide a vehicle audio device.

[0009]

[Means for Solving the Problems] Therefore, the present invention has the following features:
For vehicles, comprising a receiving means for receiving broadcast radio waves, an intermediate frequency range amplifying means connected to the receiving means, and an audio reproducing means connected to the intermediate frequency range amplifying means via an audio output forming means. In the acoustic device, a received signal level detecting means detects a received signal level at the intermediate frequency band amplifying means, a noise level detecting means detects a noise level of the audio signal at the audio reproducing means, and a predetermined reference signal. storage means for storing the correlation between the detected value of the received signal level detection means and the peak value of the audio signal level when the received signal level is received; Based on the detection value of the detection means and the correlation stored in the storage means, a peak value of the audio signal level corresponding to the received signal level is calculated, and the calculated value and the detection value of the noise level detection means are calculated. A calculation means is provided for calculating the SN ratio from the following.

0010

According to the present invention, since the storage means is provided, the level of the received signal when a predetermined reference signal (for example, a signal at a reference modulation level such as 100% modulation or 30% modulation) is received. The correlation between the detection value of the detection means and the peak value of the audio signal level can be stored. Further, since the calculation means is provided, when a broadcast radio wave is received by the reception means, the reception signal level is determined based on the detected value of the reception signal level detection means and the correlation stored in the storage means. It is possible to calculate the peak value of the audio signal level corresponding to , and to calculate the SN ratio from the calculated value and the detected value of the noise level detection means.

In this case, the detection value of the received signal level detection means is converted into the peak value of the audio signal level when the predetermined reference signal is received, according to the correlation stored in the storage means. , it is possible to accurately measure the signal level of the output signal without being affected by fluctuations in received electric field strength or modulation level of received radio waves. As a result, an accurate S/N ratio can be measured during actual driving, and appropriate sensitivity evaluation can be performed for the receiving system of the vehicle acoustic device.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. As shown in FIG. 1, in the vehicle audio device 1 according to the present embodiment, a tuner 4 is connected via a changeover switch 3 to an antenna 2 that can receive broadcast radio waves from a broadcast station. The tuner 4 includes, from the front side to the rear side, for example, a high frequency amplifier 5 that directly amplifies the tuned high frequency signal of the desired broadcast station, an intermediate frequency amplifier 6, a detector 7, and a main amplifier 8. are arranged in order, and a speaker 9 is connected to the main amplifier 8. Further, the intermediate frequency amplifier 6 is equipped with a signal meter (S meter) capable of displaying the strength of the received radio wave as a DC voltage value, as a received signal level detection means in the present application.
10 is attached, and the voltage value of the S meter 10 (S meter voltage) is input to an arithmetic unit 14, which will be explained in detail later.

In the normal state in which the changeover switch 3 is switched and set to connect the antenna 2 and the tuner 4, the broadcast radio waves received by the antenna 2 select the high frequency signal of the desired broadcasting station from among the high frequency signals. After the signal is selected and tuned, it is suitably amplified by the high frequency amplifier 5, and then converted to a constant intermediate frequency by a frequency conversion circuit (not shown). This intermediate frequency signal is suitably amplified by the intermediate frequency amplifier 6, and then converted into an audio signal by the detector 7, and then sent to the main amplifier 8. After being amplified by the main amplifier 8, the sound is output from a speaker 9 into the vehicle interior.

In this embodiment, more preferably, a signal generator 12 capable of generating a reference signal of a predetermined modulation level is disposed on the input side of the tuner 4, and the changeover switch 3
By switching the signal generator 12 and connecting the signal generator 12 to the tuner 4, a reference signal of a predetermined modulation level generated by the signal generator 12, that is, 100% modulation at 1 KHz, which is the reference when measuring the S/N ratio, can be obtained. The resulting signal can be input to the tuner 4.

In this embodiment, a fast Fourier transformer 13 is connected between the tuner 4 and the speaker 9, and performs fast Fourier transform on the audio signal output from the tuner 4 to the speaker 9. , the frequency spectrum pattern of the audio signal can be obtained. and,
The measurement data of the frequency spectrum pattern is input to the arithmetic unit 14.

The arithmetic unit 14 is configured with a microcomputer as its main part, for example, and when the changeover switch 3 is switched to the signal generator 12 side, the S meter voltage from the S meter 10 and the high speed From the measurement data of the frequency spectrum pattern from the Fourier transformer 13, a reference signal (1 KHz, 100%) with a predetermined modulation level is
The correlation between the S meter voltage and the peak value (peak voltage) of the audio signal level when a modulated signal is received can be calculated, and the correlation can be stored in the attached memory 15. On the other hand, the changeover switch 3 is connected to the antenna 2.
When switched to the side, the fast Fourier transformer 1
3, the noise level is calculated based on the measurement data of the frequency spectrum pattern, and the S meter 10
The received signal level during actual driving is converted to the signal level when the reference signal is received, based on the S meter voltage from the S meter voltage and the correlation stored in advance in the memory 15. /N ratio can be calculated.

Measurement of the S/N ratio during actual driving will be explained below. First, set the changeover switch 3 to the signal generator 1.
2 side, the output signal of the signal generator 12 is set to a 100% modulated signal at 1 KHz and input to the tuner 4. Next, while changing the signal strength from a small signal to a large signal, the S meter voltage is recorded, and the audio signal at each signal strength is fast Fourier transformed, and each peak value Smax ( f) respectively. This data is then stored in the memory 15 as a correlation between the S meter voltage and the peak value Smax(v) of the audio signal level. An example of the above correlation is shown in the graph of FIG.

After storing the above correlation in the memory 15, the selector switch 3 is switched to the antenna 2 side. In this state, when the antenna 2 receives a broadcast radio wave, for example while traveling in the field, the audio signal corresponding to the broadcast radio wave is fast Fourier transformed by the fast Fourier transformer 13, and the frequency spectrum pattern of the audio signal is obtained. This frequency spectrum pattern is expressed as a graph of changes in audio signal level with respect to the frequency axis, as an example of which is shown in FIG. Next, from this frequency spectrum pattern, as shown in FIG. 4, a histogram accumulated on the frequency axis is created, and the appearance frequency of each signal level is counted. Since a signal level that appears particularly frequently compared to other signal levels (see signal level N in FIG. 4) can be identified as a noise component included in the audio signal, from this histogram, The noise level N during actual driving can be detected.

On the other hand, the S meter voltage during the field driving is inputted to the arithmetic unit 14. The arithmetic unit 14 calculates the S meter voltage during actual driving based on the correlation between the S meter voltage stored in the memory 15 and the peak value Smax(v) of the audio signal level, and calculates the S meter voltage when the reference signal is received. It is converted into a peak value Smax(v) of the audio signal level. And Smax(v
)/N, the S/N during actual driving can be calculated.
Now you can find the ratio.

The above calculations are performed one after another, and a graph of the calculation results is drawn on the recording paper 16, for example, as shown in FIG. In this case, the paper feed motor 17 is driven by the pulses of the odometer 18, and the recording paper 16 is fed in proportion to the travel distance, thereby making it possible to draw a graph.

As explained above, according to this embodiment, since the memory 15 is provided, the S meter voltage and the audio signal when a predetermined reference signal (for example, 1 KHz, 100% modulation signal) is received The correlation between the level and the peak value can be stored. Furthermore, since the arithmetic unit 14 is provided, when the antenna 2 receives broadcast radio waves, based on the S meter voltage and the correlation stored in the memory 15, an audio signal corresponding to the S meter voltage is generated. The peak value Smax(v) of the signal level is calculated, and Smax(v) is calculated from the calculated value Smax(v) and the noise level N.
The N ratio can be calculated.

In this case, the S meter voltage is:
According to the correlation stored in the memory 15, it is converted to the peak value Smax(v) of the audio signal level when the predetermined reference signal is received, so fluctuations in the received electric field strength or fluctuations in the modulation level of the received radio waves It is possible to accurately measure the signal level of the output signal without being affected by As a result, the accurate S/N ratio was measured during actual driving, and the reception system of the above-mentioned vehicle acoustic device was
This allows for appropriate sensitivity evaluation.

By installing an audio device capable of measuring the S/N ratio during actual driving as described above, for example, the tuner can be stored in advance with the correlation between the S meter voltage and the maximum value of the audio signal level. By automatically measuring the S/N ratio while driving, and applying muting when the S/N ratio deteriorates below a predetermined value, it is possible to eliminate urban noise, especially when the received electric field strength changes irregularly. For external noise such as
This can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram schematically showing the circuit configuration of a vehicle audio device according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of the correlation between the S meter voltage and the maximum value of the audio signal level.

FIG. 3 is a graph showing an example of a frequency spectrum pattern obtained by performing fast Fourier transform on an audio signal.

FIG. 4 is a graph showing an example of a histogram showing the frequency of appearance of audio signal levels in the frequency spectrum pattern.

FIG. 5 is an explanatory diagram showing an example of data of calculated values recorded by the vehicle audio device.

[Explanation of symbols]

1...Vehicle audio equipment 2...Antenna 4...Tuner 6...Intermediate frequency amplifier 9...Speaker 10...Signal meter (S meter) 13...Fast Fourier transformer 14... Arithmetic unit 15...Memory N...Noise level

Claims (1)

[Claims] 1. A receiving means for receiving broadcast radio waves, an intermediate frequency range amplifying means connected to the receiving means, and an audio reproduction means connected to the intermediate frequency range amplifying means via an audio output forming means. A vehicle acoustic device comprising: a received signal level detecting means for detecting a received signal level at the intermediate frequency band amplifying means; a noise level detecting means for detecting a noise level of the audio signal at the audio reproducing means;
A storage means is provided for storing a correlation between a detection value of the received signal level detection means and a peak value of the audio signal level when a predetermined reference signal is received, and when a broadcast radio wave is received by the reception means. , calculates the peak value of the audio signal level corresponding to the received signal level based on the detected value of the received signal level detection means and the correlation stored in the storage means, and calculates the peak value of the audio signal level corresponding to the received signal level, and calculates the peak value of the audio signal level corresponding to the received signal level, and calculates the peak value of the audio signal level corresponding to the received signal level, and calculates the peak value of the audio signal level corresponding to the received signal level A vehicular audio device characterized by comprising a calculating means for calculating an SN ratio from a detected value of the detecting means.