JPH11234788A - Audio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce low frequency sound even with a speaker of a small diameter, to eliminate noise with a simple configuration and to avoid production of a sense of incongruity. SOLUTION: A frequency doubler shifter 11 converts an audio signal ASin into an audio signal whose frequency is multiple of (n) (e.g. twice). A band-pass filter 12 extracts a low frequency component in a frequency range of 60-200 Hz that is reproduced with a small diameter speaker from the frequency- converted audio signal. A combiner circuit 14 parts together the audio signal before frequency conversion with the low frequency component signal (the signal with a frequency range doubling a frequency range of 30-100 Hz of the original low sound signal) and gives the combined signal to the small diameter speaker.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device, and more particularly, to the reproduction of bass sound even with a small-diameter speaker.
The present invention relates to an audio device that can be emphasized.

[0002]

2. Description of the Related Art A large-diameter speaker cannot be mounted on an in-vehicle audio device due to space limitations in a vehicle cabin. For this reason, there is a problem that a low-pitched sound reproduction environment is poor and a sound with good sound quality cannot be reproduced and output. Therefore, an audio device having a configuration as shown in FIG. 2 has been proposed so that even a small-diameter speaker can reproduce and emphasize a low-frequency signal. In FIG. 2, reference numeral 1 denotes a band limiting filter configured by a band-pass filter, which extracts a low-frequency signal component that cannot be reproduced by a small-diameter speaker, for example, an audio signal component of 30 to 100 Hz when an audio signal ASin is input. And output it. 2 is a frequency doubler shifting device, converts the low-frequency signals S ₁ of 30~100Hz extracted by band-limiting filter 1 to the signal S ₂ of the doubled frequency, converted small-diameter speaker band playable ones, 3 is the envelope processing unit, in order to remove noise caused by the discontinuity of the signal S ₂ output from the frequency doubling shifting device, discontinuity is subjected to envelope processing to the signal S ₂ Is reduced to some extent to make it smoother. 4 is a delay circuit for delaying the audio signal ASin by the time required for the low-frequency signal extraction, frequency doubling processing, and envelope processing;
Reference numeral 5 denotes a synthesizing circuit for synthesizing a signal output from the envelope processing unit and an audio signal delayed by the delay circuit and outputting the synthesized signal.

A method of doubling the frequency of the input signal S _{1 in} the frequency doubling shifter 2 is shown in FIG.
Input signal (as a sine wave for explaining are) sampling the S ₁ at a predetermined sampling rate, and stored in a memory (not shown) by AD converting the (2) sampling data, (3) Thereafter, every If the read sampling data from the memory (black dot data signals S ₁₎ at a sampling rate the same speed, and outputs a signal S ₂ (black circle data signal S _2), was Yomiki' the data stored in (4) memory,
The same data is again read out and output every other one from the beginning. Figure 3 stores 40msec component in the sampling data of the signals S ₁ to the memory, and thereafter, reads out the data in every other than the memory and 20msec component signal S ₂ of the data (first reading) was Yomiki' when the same data repeatedly read out of 20msec component of the signal S ₂ data again (second reading), the signal of the total 40 msec S
₂ data.

In the method of doubling the frequency of the input signal, the last data D _L of the first time of the signal S ₂ is used.
Corresponds to the last data D _L 'of the input signal S ₁ and the signal S ₂
The first data D _S 2 nd of corresponding to the first data D _S of the input signal S ₁ '. Therefore, if the first and last data 40msec component of the signal S ₁ is smoothly connected, the discontinuity is not generated in the first and second connecting portions of the signal S _2. However, the first and last generally 40msec data signals S ₁ is not smoothly connected. Therefore, first and discontinuities in the second connecting portion of the signal S ₂ NC1, NC2 is generated. This discontinuity causes noise. Therefore, in the envelope processing unit 3, as shown in FIG.
C1, the multiplication coefficient is small in NC2, generates a window function WF to increase as the multiplication coefficient away from discontinuities, to some extent smoothed discontinuities by multiplying the window function to the signal S _2, noise The occurrence has been reduced.

[0005]

According to the envelope processing, noise due to a discontinuous portion of a signal can be reduced.
The sound fluctuates, and depending on the type of the audio source, there is a case where a considerable sense of incongruity appears. This envelope processing intended for multiplying a window function shown in FIG. 4 to the signal S _2, or to increase the multiplication factor or gain, in equivalent to or smaller Therefore, and out the sound, not out This is because the sound is slightly wavy and beats are generated, and the music causes a sense of incongruity. Further, the proposed audio device has a problem that both a bandpass filter and an envelope processing unit are required. or,
The proposed audio device has a problem that the processing amount is large because the envelope processing is necessary, and the load of the DSP processing in the case of the DSP configuration becomes large. As described above, an object of the present invention is to provide an audio apparatus which does not require envelope processing, can eliminate noise with a simple configuration, eliminates discontinuity, and does not cause discomfort.

[0006]

According to the present invention, there is provided a frequency conversion circuit for converting an audio signal into an audio signal having a frequency n times (n> 1, for example, n = 2), 2) A filter for outputting a low-frequency component of a frequency-converted audio signal, and (3) an audio device having a synthesizing circuit for synthesizing and outputting the audio signal before frequency conversion and the filter output signal.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (a) Overall Configuration FIG. 1 is a block diagram showing the main parts of an audio apparatus according to the present invention.
Sin is an audio signal input from an audio source (not shown) via a graphic equalizer or the like;
t is an audio signal input to an audio circuit such as an amplifier. Numeral 11 is a frequency doubler, which converts the frequency of the input audio signal ASin to double the frequency, and 12 is a band limiting and noise removing filter, for example, a band-pass filter having a band of 60 to 200 Hz. . Reference numeral 13 denotes a delay circuit for delaying the audio signal ASin by the time required for the frequency doubling process and the filtering process. Reference numeral 14 denotes a signal having a band of 60 to 200 Hz output from the band-pass filter 12 and all signals delayed by the delay circuit 13. This is a synthesizing circuit for synthesizing the audio signal of the band and outputting the audio signal ASout.

(B) Frequency double shift device In the frequency double shift device 11, 11a is a sampling and holding circuit for sampling the audio signal ASin at a predetermined speed fs, 11b is an AD converter for performing AD conversion on the sampled and held signal, Reference numeral 11c denotes a memory for storing AD-converted digital audio data, and includes memory units A and B. Audio data for 40 msec is alternately written into these memory sections A and B, and data is alternately read out. When data is written in one memory unit, data is read out from the other memory unit every other data. 11d is a DA converter for converting digital audio data read from the memory into analog, and 11e is a read / write control unit. The read / write control unit 11e (1) alternately writes AD conversion data into the memory units A and B every 40 msec at the sampling frequency fs, and (2) the memory unit where data is not being written, that is, the data has already been written. Every other data from the memory unit is read and output at the same speed as the sampling speed (first reading), and when the data stored in the memory is completely read, the same data is placed again from the beginning of the memory. In the same manner as above (2nd reading). As described above, as shown in FIG.
The frequency of Sin (= S ₁ ) is doubled and output as a signal S ₂ .

(C) Operation The low-frequency band in which the small-diameter speaker cannot reproduce is 30 to 100 Hz. Therefore, the frequency of the audio signal in this band is doubled, that is, the unreproducible band of 30 to 100 Hz is converted to a reproducible band of 60 to 200 Hz, and this signal is input to a small-diameter speaker. In addition, the bass can be reproduced and emphasized even with a small-diameter speaker. This is the principle that bass can be reproduced and emphasized even with a small-diameter speaker.
Therefore, in FIG.
The frequency of the audio signal of the entire band is not limited to 0 Hz but is 2
Converted to 2 times, and the band is 60 to 200Hz by the band pass filter 12.
Is extracted and output. As a result, a signal of 30 to 100 Hz that cannot be reproduced by a small-diameter speaker can be reproduced by 60
The signal is converted into a signal of up to 200 Hz and input to the synthesis circuit 14. Here Notably, a band-pass filter 12 band 60～200Hz, discontinuities NC1 contained in the signal S ₂ output from the frequency twice the shift device 11, NC2
(See FIG. 3).
This is because the frequency of the noise generated by the discontinuous portion of the signal is relatively high, and is often higher than the required band (60 to 200 Hz).

On the other hand, the delay circuit 13 delays the audio signal ASin of the entire band by a predetermined time and inputs it to the synthesizing circuit 24. 40 ms for the memory sections A and B of the frequency doubler 11
If data is written and read alternately in units of ec, a delay of 40 msec occurs in the frequency double shift device 11, so the delay time of the delay circuit 13 is 40 msec. The synthesizing circuit 14 outputs a signal having a band of 60 to 200 Hz (30 to 100 Hz of the original bass signal frequency output from the bandpass filter 12).
The combined signal ASout is input to a small-diameter speaker via an amplifier (not shown) or the like. As a result, even a small-diameter speaker can reproduce and output low-pitched sound, and can improve the sound quality of reproduced sound. In the above description, the frequency of the audio signal is doubled. However, the frequency is not necessarily doubled. There may be. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0011]

As described above, according to the present invention, an original audio signal is converted into an audio signal whose frequency is n times (for example, twice), and a low-frequency component which can be reproduced by a small-diameter speaker from the frequency-converted audio signal is converted. Since the extracted audio signal and the low-frequency component are synthesized and output, by inputting the synthesized signal to a small-diameter speaker, bass sound included in the original audio signal can be reduced even with a small-diameter speaker. Playback and emphasis can be performed, and the sound quality of the reproduced sound can be improved. Further, according to the present invention, since noise generated due to a discontinuous portion included in the frequency-converted audio signal can be removed by the filter, a high-quality sound without noise can be output.

Further, according to the present invention, the filter is used for 60 to 200 hours.
It is only necessary to extract and output the z band component, and no envelope processing is required, so that sound fluctuation does not occur as in the related art, and it is possible to enjoy a high-quality reproduced sound without a sense of incongruity. Further, according to the present invention, a frequency conversion circuit for converting the frequency of an original audio signal, a filter for outputting a low-frequency component of the frequency-converted audio signal, and combining and outputting the original audio signal and the filter output signal Therefore, it can be realized with a simple configuration. In addition, since the envelope processing is unnecessary, the processing amount can be remarkably reduced in the case of using a DSP.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an audio device of the present invention.

FIG. 2 is a configuration diagram of a proposed audio device.

FIG. 3 is an explanatory diagram of a method of doubling a frequency.

FIG. 4 is an explanatory diagram of an envelope process.

[Explanation of symbols]

11. Frequency doubler 12. Filter for band limitation and noise removal (for example, band pass filter) 13. Delay circuit 14. Synthesis circuit

Claims (1)

[Claims] 1. An audio signal having an n-fold frequency (n> n)
1) a frequency conversion circuit for converting the audio signal into an audio signal, a filter for outputting a low-frequency component of the frequency-converted audio signal, and a synthesis circuit for synthesizing and outputting the audio signal before frequency conversion and the filter output signal. An audio device, characterized in that: