JP4872086B2 - High frequency signal interpolator - Google Patents

Description

  The present invention relates to a high-frequency signal interpolating apparatus suitable for use in digital audio equipment with compression such as MP3, telephones and the like. Specifically, the high frequency signal missing due to compression or the like is artificially interpolated.

  In recent years, audio data representing audio such as music has been actively used by being distributed via a network such as the Internet or recorded on a recording medium such as an MD (Mini Disk). In this way, in audio data distributed over a network or recorded on a recording medium, in order to avoid an increase in the amount of data and an increase in occupied bandwidth due to an excessively wide band, generally music to be supplied, etc. Of these, the components above a certain frequency are removed.

  That is, for example, in the audio data in the MP3 (MPEG1 audio layer 3) format, frequency components of about 16 kilohertz or more are removed. Further, in the audio data in the ATRAC3 (Adaptive TRansform Acoustic Coding 3) format, frequency components of about 14 kilohertz or more are removed.

  The reason why the high frequency components are removed in this way is that it is considered unnecessary to use frequency components that exceed the audible range in relation to human hearing. However, it has been pointed out that the sound quality of the signal from which the high frequency components have been completely removed as described above is slightly changed and the sound quality is deteriorated compared to the original music. .

  On the other hand, in the conventional high frequency signal interpolation, an interpolated signal is generated by frequency-converting the interpolated signal (for example, see Patent Document 1), or a high-frequency signal having no correlation is added to the original signal. Is known (for example, see Patent Document 2).

That is, the technique described in Patent Document 1 generates an interpolation signal by frequency-converting an interpolated signal in high-frequency signal interpolation. Moreover, the technique of patent document description 2 extracts the high frequency component of the signal from a white noise generator, and adds the high frequency signal without correlation to an original signal.
JP 2004-184472 A Japanese Patent Laid-Open No. 2-311006

  However, the techniques described in Patent Documents 1 and 2 both interpolate the removed high frequency signal, but the technique described in Patent Document 1 uses a DSP (Digital Signal Processor) for frequency conversion. A complicated circuit configuration such as use is required. Further, the technique described in Patent Document 2 cannot obtain a sufficient effect because it is a high-frequency signal having no correlation.

  On the other hand, the present inventor previously disclosed a “high-frequency signal interpolation method and high-frequency signal interpolating apparatus” in Japanese Patent Application No. 2005-210124 that extracts the harmonic part of the envelope component of the original signal and interpolates the missing high-frequency component. As filing. In the prior invention, a high-frequency component is formed by using a Hilbert transform that decomposes a signal into a real part and an imaginary part in order to extract a harmonic part, and performing a square root calculation of the real part and the imaginary part. As a result, the invention of the prior application is able to perform extremely high-quality interpolation, and has been highly evaluated, such as being used in commercially available audio products.

  However, in the prior invention, a relatively large amount of calculation processing is required for the Hilbert transform and the square root calculation for extracting the harmonic part. For this reason, particularly in a small-sized device, there is a problem that the load on the processing circuit increases when the processing circuit is used in combination with other functions (video display or the like) performed by the device. Further, strengthening the capacity of the processing circuit only for increasing the load causes a problem in terms of economy because a required circuit device becomes expensive. Furthermore, the DSP used for such signal processing has a problem of high power consumption.

  Therefore, the present inventor further detects the peak value of the original signal, generates a rectangular wave obtained by holding the detected peak value, extracts the harmonic part of the generated rectangular wave, and adds it to the original signal. As a result, a “High-frequency signal interpolation method and high-frequency signal interpolation device” for interpolating the missing high-frequency component was filed as Japanese Patent Application No. 2006-282830.

  That is, in FIG. 7, the input terminal 1 is supplied with a reproduction signal from a device with compression processing such as MP3 or ATRAC3 as an original signal. The original signal supplied to the input terminal 1 is supplied to a peak value detection / holding circuit 2 that detects and holds a peak value to generate a rectangular wave signal. The rectangular wave signal generated here includes harmonic components of the input signal. This rectangular wave signal is supplied to a high pass filter (HPF) 3 to extract a harmonic component.

  Further, the original signal from the input terminal 1 is supplied to a delay circuit 4 corresponding to the processing time in the above-described peak value detection / holding circuit 2, and a signal with a uniform delay time is supplied to a low-pass filter (LPF) 5. Then, the signal from which the high frequency component is removed is taken out. The output signals of the high pass filter 3 and the low pass filter 5 are added by the adder circuit 6 and output to the output terminal 7. As a result, a signal on which the high frequency signal is superimposed (emphasized) is obtained from the output terminal 7.

  In this way, for example, high-frequency signal interpolation is performed on a digital audio signal reproduced from a device with compression such as MP3 or ATRAC3. That is, the high frequency signal can be interpolated by adding the harmonic portion of the rectangular wave signal formed by the peak value holding circuit 2 to the original signal from which the high frequency component has been removed. Therefore, the calculation used in this process is only the detection of the peak value and the processes of the high pass filter 3 and the low pass filter 5.

  In this process, when the original signal supplied to the input terminal 1 has a waveform as shown by a solid line in FIG. 8, the peak value of the original signal is detected as indicated by a circle in the figure. . Therefore, when this peak value is held, a rectangular wave signal as shown by a dotted line in the figure is formed. Since this rectangular wave signal is a signal formed with the harmonic components included in the input signal emphasized, the high frequency signal of the input signal can be obtained by extracting the harmonic part from this rectangular wave signal. Is taken out.

  In FIG. 8, no harmonic component is generated when the original signal (solid line) has a constant amplitude as in the period indicated by the symbol a. However, such a signal is originally considered to have few high frequency components, and it can be seen that the present invention is faithful to such a signal. During the period of the symbol a, the original signal supplied to the input terminal 1 is supplied to the adder circuit 6 through the low-pass filter 5, but no harmonic component is supplied from the HPF 3 to the adder circuit 6. The original signal is output without high frequency emphasis.

  As described above, the harmonic component held by the rectangular wave obtained by performing peak detection and holding of the input signal is very close to the high frequency component characteristic of the original signal. Therefore, if the original signal is interpolated with this harmonic component, extremely good high-frequency signal interpolation can be performed. 9A shows a signal before interpolation, and FIG. 9B shows a signal after interpolation. As can be seen from FIG. 9, according to the present invention, extremely good high-frequency signal interpolation is performed. In this manner, in the prior invention, high-frequency signal interpolation can be realized with a relatively small amount of calculation.

  However, even in this prior invention, there were cases where the burden of calculation processing was still large. Further, when such signal processing is performed digitally, processing by the high-pass filter 3 and the low-pass filter 5 also becomes a heavy burden. Therefore, a DSP is still required to realize these processes, and such a DSP still has a problem of high power consumption.

  The present invention has been made in view of such problems, and an object of the present invention is to reduce the burden of calculation processing by using an analog circuit, and is good without using a DSP. Therefore, it is possible to realize high-frequency signal interpolation.

  In order to solve the above problems and achieve the object of the present invention, the invention described in claim 1 includes means for detecting a peak value of an original analog signal supplied to an input terminal, and a detected peak value. Means for generating a corresponding pulse width modulation signal, means for extracting a harmonic part of the generated pulse width modulation signal, and means for adding the extracted harmonic part to the original analog signal supplied to the input terminal A high-frequency signal interpolating device characterized by comprising:

  In the high-frequency signal interpolating apparatus according to claim 2, the original analog signal supplied to the input terminal is band-limited and supplied to the analog-digital conversion input of the microcomputer, and the microcomputer detects the peak value. And generating a pulse width modulation signal.

  In the high-frequency signal interpolating device according to claim 3, the peak value is detected when the central value of three consecutive sampled values is equal to or greater than the immediately preceding value and greater than the immediately following value. The center value is detected as a peak value.

  According to a fourth aspect of the present invention, the pulse width modulation signal is generated by presetting a peak value in a counter and down-counting with a predetermined clock signal.

  The high-frequency signal interpolating device according to claim 5 is characterized in that means for generating a rectangular wave by converting the pulse width modulation signal into a direct current is provided.

  According to the high frequency signal interpolating apparatus of the present invention, the peak value of the original analog signal is detected, and the harmonic part of the rectangular wave generated by the pulse width modulation signal generated according to the peak value is extracted and interpolated. Therefore, a good high frequency signal can be formed with a very simple configuration, and practical high frequency signal interpolation can be performed without increasing the load on the processing circuit.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an embodiment of an apparatus to which a high frequency signal interpolation apparatus according to the present invention is applied. In the high-frequency signal interpolating device of this example, an analog audio signal reproduced from a device with compression processing such as MP3 or ATRAC3 is supplied as an original analog signal.

  Therefore, the original analog signal supplied to the input terminal 11 is supplied to an analog low-pass filter (LPF) 12 having a cutoff frequency of 10 kHz, for example. Here, a maximum frequency of 10 kHz is assumed as the fundamental frequency of the musical instrument. A signal whose band is limited by the low-pass filter 12 is supplied to the A / D conversion input 14 of the microcomputer 13. Further, in the microcomputer 13, the peak value detection 15 of the input signal is performed, and a pulse width modulation (PWM) 16 is performed on the detected peak value to extract the PWM signal.

  The PWM signal extracted from the microcomputer 13 is supplied to an analog low-pass filter (LPF) 17 that removes 100 kHz or more, which is the PWM carrier frequency, to form a rectangular wave. This rectangular wave signal is supplied to an analog high pass filter (HPF) 18 having a cut-off frequency of 20 kHz for extracting a harmonic part. Further, the high frequency signal extracted from the high pass filter 18 is supplied to the adder 19, added to the original analog signal from the input terminal 11, and extracted to the output terminal 20.

  Therefore, in the high-frequency signal interpolating device according to the present invention, since the low-pass filters 12, 17 and the high-pass filter 18 are all formed of analog circuits, they do not become a burden of signal processing and consume very little power.

  Further, in the signal processing, besides using the existing A / D conversion input 14 for the microcomputer 13, only the peak value detection 15 and the pulse width modulation (PWM) 16 are performed, so that the signal processing load is reduced. The hardware can be realized by a so-called CPU (Central Processing Unit). Such a CPU consumes very little power.

  Furthermore, since the processing by the CPU can be performed at a higher speed than a general audio signal, the delay circuit used in the circuit of the prior invention is not required. Therefore, the circuit configuration can be simplified and no extra circuit is provided, so that the product price can be reduced.

  Next, the operation of the peak value detection 15 in the high frequency signal interpolating device of FIG. 1 will be described based on the flowchart shown in FIG.

  As shown in FIG. 2, when the process starts, first, a variable n is initialized to “n = 1” (step S1), and then, three consecutive sampling values An− of the supplied digital audio signal are obtained. 1, An, An + 1 are extracted (step S2). These three sampling values An-1, An, and An + 1 are compared, and it is determined whether or not the value An-1 = An and the value An> An + 1 (step S3).

  If the determination in this determination step S3 is Yes, then the value An is taken out as a peak value (step S4). When the value An-1 = An and the value An> An + 1 is not satisfied (No) in the determination step S3, that is, when An-1 ≠ An or the value An <An + 1, the value An-1 <An. And it is judged whether or not the value An> An + 1 (step S5). If the determination in this determination step S5 is Yes, the process similarly proceeds to step S4, and the value An is extracted as the peak value.

  That is, if An satisfies one of the relationships between the determination step S3 and the determination step S5, that is, if the sampling value of the original signal satisfies the relationship shown in FIG. The value An is held. On the other hand, if it is determined that An does not satisfy any of the relationship between the determination step S3 and the determination step S5 (No), n is set to n + 1 and the process returns to step S2 (step S6). In this way, the process of detecting and holding the peak value of the original signal is repeatedly performed every sampling period of the digital audio signal.

  Further, FIG. 4 shows another example of the flowchart. In this example, after step S2, three sampling values An-1, An, and An + 1 are compared, and it is determined whether or not the value An-1> An (step S3 '). If it is determined No in this determination step S3 ′, it is subsequently determined whether or not the value An> An + 1 (step S5 ′). If it is determined Yes in the determination step S5 ', the value An is extracted as a peak value (step S4).

  Also in this case, if the sampling value of the original signal satisfies the relationship shown in FIG. 3A or B, the value An when the peak occurs is held. On the other hand, when it is determined Yes in the determination step S3 ′ or when it is determined No in the determination step S5 ′, n is set to n + 1 and the process returns to the step S2 (step S6). In this way, the process of detecting and holding the peak value of the original signal is repeatedly performed every sampling period of the digital audio signal.

  The operation of the pulse width modulation (PWM) 16 in the high frequency signal interpolating device of FIG. 1 will be described based on the flowchart shown in FIG.

  As shown in FIG. 5, when the process starts, it is first determined whether or not a preset pulse has been input (step S11), and when it has not been input (No), this step S11 is repeated. When a preset pulse is input in step S11 (Yes), the input peak value is preset to the value N (step S12).

  Further, it is determined whether or not the value N = 0 (step S13). When N ≠ 0 (No), [N = N-1] is set (step S14), and step S13 is repeated. If N = 0 in step S13 (Yes), the process returns to step S11.

  Thus, for example, when a preset pulse as shown in FIG. 6A is supplied, the subsequent processing time in steps S13 and S14 is set to the clock cycle as shown in FIG. Is called. Then, as shown in FIG. 6C, a pulse width modulation (PWM) signal corresponding to the input peak value is formed until the count value N becomes zero.

  As described above, in the configuration of this example, signal processing for high-frequency signal interpolation can be realized only by simple processing of peak value detection and pulse width modulation (PWM), and signal processing is not burdened on the circuit. It can be implemented with less. Furthermore, by using an analog circuit for the low-pass filter and the high-pass filter, it is possible to further reduce the burden on the processing circuit and perform good high-frequency signal interpolation without using a DSP. .

  As described above, according to the high frequency signal interpolating device of the present invention, the peak value of the original analog signal supplied to the input terminal is detected, and the pulse width modulation signal corresponding to the detected peak value is generated and generated. By taking out the harmonic part of the pulse width modulation signal and adding it to the original analog signal supplied to the input terminal, a good high-frequency signal is formed with a very simple configuration, and practical high-frequency signal interpolation is performed. Is something that can be done.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the claims.

It is a block diagram which shows the structure of one Embodiment of the apparatus to which the high frequency signal interpolation apparatus by this invention is applied. It is a flowchart figure of an example which shows the process of a peak value detection. It is a wave form diagram for the explanation. It is a flowchart figure of the other example which shows the process of peak value detection. It is a flowchart figure of an example which shows the process of pulse width modulation (PWM). It is a wave form diagram for the explanation. It is a block diagram which shows the structure of the high frequency signal interpolation apparatus which this inventor proposed previously. It is a wave form diagram for the explanation. It is a wave form diagram for explanation of the effect.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Input terminal, 12 ... Analog low pass filter (LPF), 13 ... Microcomputer, 14 ... A / D conversion input, 15 ... Peak value detection, 16 ... Pulse width modulation (PWM), 17 ... Analog low pass filter (LPF) 18 ... analog high pass filter (HPF), 19 ... adder, 20 ... output terminal

Claims (5)

Means for detecting the peak value of the original analog signal supplied to the input terminal;
Means for generating a pulse width modulation signal according to the detected peak value;
Means for extracting a harmonic portion of the generated pulse width modulation signal;
And a means for adding the extracted harmonic part to the original analog signal supplied to the input terminal. In the high frequency signal interpolating device according to claim 1,
Band-limiting the original analog signal supplied to the input terminal and supplying it to the analog-digital conversion input of the microcomputer,
The high-frequency signal interpolating apparatus, wherein the microcomputer detects the peak value and generates the pulse width modulation signal. In the high frequency signal interpolation apparatus according to claim 1 or 2,
The detection of the peak value is to detect the central value as the peak value when the central value of three consecutive sampled values is equal to or greater than the immediately preceding value and greater than the immediately following value. A high-frequency signal interpolating device. In the high frequency signal interpolation apparatus according to claim 1 or 2,
The pulse width modulation signal is generated by presetting the peak value in a counter and down-counting with a predetermined clock signal. In the high frequency signal interpolation apparatus according to claim 1 or 2,
Means for generating a rectangular wave by converting the pulse width modulation signal into a direct current is provided.

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