JP2008219844A - Highly-efficient low-pitched sound emphasizing technology - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide by a simple basic circuit: acoustic equipment which achieves efficient low-pitched sound emphasis that allows a reduction in heat generation of a speaker driving part; an acoustic signal in which the efficient low-pitched sound emphasis is executed; and a special effect device for a distortion musical instrument in which improvement in perception of fundamental tones is executed. <P>SOLUTION: Improvement in perception is made by inducing cocktail party effects while executing a phase shift in a state of making a low-pitched sound emphasizing component utilizing beats generated by higher-harmonic-wave addition and a missing fundamental phenomenon, and a low-pitched sound emphasizing component generated by dynamic amplitude correction, as amplitude functions of an input signal. Efficient low-pitched sound emphasis is achieved by further increasing a maximum amplitude limit amount in a low-pitched sound region compared with the conventional technology. Distortion occurring due to expansion of a bandwidth of an added higher harmonic wave is utilized in the special effect device for a distortion musical instrument so as to achieve similar special effects in the series connection between distortion and a flanger. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an electroacoustic apparatus, and more particularly to a harmonic generator and method necessary for high-efficiency reproduction of a sound signal in a low-frequency region.

As a bass emphasis technique using a harmonic generator, a technique of N.B.Philips Fleuran Penfabrikken in the Netherlands has been disclosed (see Patent Document 1).

As a bass emphasis technique using a harmonic generator, a technique of Korg Co., Ltd. (see Patent Document 2) is disclosed.

As a bass emphasis technique that combines the harmonic generator and the dynamic control of the bass, a technique (see Patent Document 3) of Matsushita Electric Industrial Co., Ltd., Japan is disclosed.

As a technology for improving distortion caused by saturation of a reproduction system such as a speaker while performing bass emphasis by dynamically controlling a bass region in an acoustic signal, a technology of Afex Systems Limited, USA (see Patent Document 4) Is disclosed.

The principle that an increase in volume similar to signal enhancement is obtained in terms of hearing by adding a harmonic signal to an acoustic signal is well known as the Haas Effect.

As an example of signal enhancement that induces the Haas effect by using an audio delay device, there is bass enhancement in the sense of perception such as increased tenacity and sensation that is perceived by adding a delay sound to a bass music instrument such as a bass drum or bass guitar. It is well known as a music recording and production technique.

As an example of signal enhancement similar to the Haas effect, a bass drum, bass guitar, or other low music instrument is processed by a compressor used as a recording effect device, and the perceived stickiness or sensation is increased by increasing the harmonic components. Such low-pitched sound emphasis is well known as a music recording and production technique.

When the fundamental wave does not exist in the acoustic signal source, the beat is known as a phenomenon of perceiving the fundamental wave from listening to the harmonic component. Some of the harmonic groups (harmonic structural sounds) are called virtual pitches and have been confirmed to stimulate the hearing more strongly.

Hearing has been confirmed to discriminate between fundamental wave recognition by beat and fundamental wave recognition by virtual pitch (see Non-Patent Document 1).

The signal emphasis effect by the virtual pitch is called a missing fundamental phenomenon and is applied to improve the audibility of the band-limited sound signal source and sound equipment.
JP-A-5-328481 Japanese Patent Application No. 2000-591608 JP 2006-270698 A JP-A-6-164271 Masaura Miura's Japanese-language homepage, precedence effect by scientific structure harmonic structure sound (http://www.sug.i.ryukoku.ac.jp/miura/pdf_dom/DOM2000-07-SP-VP.pdf)

With the widespread use of multi-channel surround sound reproduction and lifestyle changes, the mainstream of household speakers is shifting to smaller products.

Small speakers are difficult to reproduce in the low frequency range due to a decrease in the enclosure volume, a rise in the minimum resonance frequency of the speaker unit, a decrease in input resistance, and so on. Countermeasures are required.

As a method for performing sufficient bass reproduction with a small speaker, a 3D system for reproducing only a bass region with a dedicated monaural speaker has been known for a long time using the fact that auditory directivity and sensitivity are lowered from around 100 Hz.

The 3D system has become widespread due to the need for low-frequency speaker installation space, standing waves generated by the installation location, and the characteristics of the dividing circuit used (phase rotation), which can cause unnatural sound localization. Not in.

The most practical method of reproducing a sufficiently low sound with a small speaker is a method of emphasizing the low frequency range of a reproduced sound with a tone control circuit or an equalizer unit. However, it is pointed out that a small speaker cannot control a sufficient reproduction volume because the effective amplitude of the voice coil is low and the input resistance is low, and the maximum output of the midrange and high range of the reproduced sound is restricted.

Bass enhancement using auditory physiology has been put into practical use as a solution. Methods include adding harmonics to the original acoustic signal (Patent Documents 1 and 2), performing dynamic amplitude correction on the bass region of the original acoustic signal (Patent Document 4), adding harmonics and dynamic amplitude. A correction (Patent Document 3) has been devised.

The present invention is based on the conventional bass emphasis that uses both harmonic addition and dynamic amplitude correction, and induces the hearth effect on the added harmonics, thereby increasing the audible enhancement amount in the bass region to the speaker. By reducing the amplitude of the input bass region and lowering the heat generation of the speaker drive unit such as a voice coil, it is intended to achieve efficient bass enhancement specialized for small speakers.

The sound signal processed by this technology is compressed in the low frequency range, even though the bass is emphasized in the sense of hearing, the spectrum is similar to the processing by the compressor, and there is no sense of incongruity when listening to large speakers or headphones. . For this reason, it is expected to be used as single-ended emphasis (synonymous with pre-emphasis in AM broadcasting) at the time of sound signal transmission by various media.

This technology expands the spectral range of additive harmonics (in the basic circuit, the spectral range of additive harmonics is limited to the low frequency range), so it can generate a distortion effect in which even harmonics are flanged. It is expected to be applied to special effects devices for distortion instruments.

In order to prevent a sense of distortion while realizing a bass emphasis effect sufficient for hearing in a small speaker, the original acoustic signal is a harmonic signal that is gently cut off at 50 dB or lower at 6 dB / oct, and sharply cut off at 200 Hz or higher at 24 dB / oct. The reason why 50 Hz or less is blocked at 6 dB / oct is that it is necessary to secure a band for reproducing the beat component when the added harmonic does not form a harmonic group (harmonic structure sound) with a virtual pitch.

In FIG. 1, which is an example of the actual circuit of FIG. 2, a phase inversion 1 circuit (1) that compensates for phase inversion in the circuit 2, and harmonic generation that controls the amplitude and spectrum of the harmonic signal generated in conjunction with the amplitude limitation. 1 circuit (2), asymmetric amplitude limit and original acoustic signal and harmonic generation Asymmetrical differential operation of output from 1 circuit generates harmonics useful for hearing and less than 50 Hz unnecessary for driving small speakers Harmonic generation 2 circuit (3) for attenuating low-frequency signals, low-pass filter (5) for sharply blocking harmful harmonic components perceived as distortion from the harmonic generation 2 circuit output, and generated harmonics Efficient bass enhancement optimized for a small speaker is realized by an adder circuit (6) for adding the component and the original sound signal and a phase inversion circuit (4) for compensating for phase inversion by the adder circuit.

Conventional bass emphasis by adding harmonics enhances the bass by the beat and missing fundamental phenomenon generated by adding harmonic components that have amplitude correlation with the original sound signal to the original sound signal. When reproducing, the speaker needs to have sufficient bass reproduction capability. When excessive harmonic addition is performed in anticipation of the missing fundamental phenomenon, the reproduced sound is distorted.

The conventional bass enhancement by dynamic amplitude correction emphasizes the bass when the speaker output is low to medium, and attenuates the low frequency when the speaker output is too high. This is a method with less harmful effects. However, it is pointed out that a sound source with a large amplitude change from a low range to a mid range, such as an impact sound, changes its tone due to low range attenuation.

In order to alleviate these problems, bass enhancement that combines harmonic addition and dynamic amplitude correction was devised. In this method, the weakness of the bass enhancement effect, which is a problem caused by harmonic addition, and the sense of distortion are suppressed. However, it is possible to mask the change in timbre due to dynamic amplitude correction by adding harmonics, and the problems of both systems can be improved.

In the present invention, the application of the articulation improvement technique by adding the flanging effect frequently used in the sound recording effect device is studied while the bass emphasis is combined with the harmonic addition and the dynamic amplitude correction.

The masking effect and cocktail party effect, which are well known as auditory physiology, are completely opposite to the result of listening to the listener under the same conditions, and the psychological state and memory of the listener greatly affect the improvement of intelligibility. Can be understood.

From these, at less than 100 Hz where the decrease in audibility is noticeable, auditory stimulation is stimulated by adding a component similar to the flanging effect to the original sound signal, and the perception level improvement (decrease in masking level) due to the cocktail party effect. I guessed it was possible.

Based on the above consideration, low-pass filtering is performed on the high-order even-order harmonic signal group and the high-order odd-order harmonic signal group (generated simultaneously by two harmonic generation circuits) that are phase-shifted as an amplitude function of the input signal. When added to the original sound signal, it was confirmed that the bass emphasis effect higher than that of the conventional method was obtained while reducing the amount of harmonic addition necessary to reproduce beats and missing fundamental phenomena.

As the means for realizing the circuit by giving priority to inexpensive, small and simple, the use of the analog computing unit of FIG. 1 is the best and advantageous from the viewpoint of realizing the cost. In addition, the use of this circuit configuration is considered to be the best when applied to all digital processing such as digital home appliances.

For applications such as recording effect devices, special effects devices for distortion instruments, and single-ended emphasis that require bold sound quality changes, the harmonic spectrum adjustment function, filter cutoff characteristic adjustment function, and input as shown in Fig. 3 The addition of a function for adjusting the addition ratio with the acoustic signal is considered to be the best mode.

FIG. 4, which is an example of a practical circuit of the present invention, realizes bass enhancement optimized for a small speaker through the following process.

When a 40 Hz sine wave having a maximum of 3 V (peak to peak value) is input as the original acoustic signal, the low-pass filter of the circuit 21 functions as an inversion buffer because the cutoff frequency is about 100 Hz. The reason why the circuit 21 is a low-pass filter is that the lagging phase component generated in the circuit 22 when a realistic signal such as a musical sound is input is canceled by the leading phase component of the circuit 21, and the clarity of the vocal component due to the null point generated in the final output This is to reduce the decrease.

The circuit 22 is a soft clip circuit in which a diode is incorporated in a negative feedback loop, and the output waveform becomes a square waveform with a gradual rise and fall of the waveform as shown in FIG. 14, and generation of low-order odd-order harmonic components can be confirmed. On the other hand, the waveform of which the amplitude is limited by a circuit called a normal compressor only changes the amplitude as shown in FIG. 13 and the spectrum does not change (when the attack time and the release time are 0 seconds).

Further, by using a multiplier in the circuit 22 so that the amplitude limiting operation start time (attack time) can be varied, the edge of the waveform can be emphasized, and the order of the harmonic component can be controlled. Furthermore, since the amplitude limiting operation start time can be relatively changed by changing the amplitude limiting operation opening time (release time), the order of the harmonic component can be controlled.

FIG. 15 shows a waveform whose amplitude is limited by a diode clip circuit, and generates a high-order odd-order harmonic component because a diode is used in a non-feedback state. Although it has a square wave shape but is a hard clip, the waveform has sharp rise and fall, and is unsuitable for applications other than distortion-type special effects devices such as distortion that do not ask for clarity of the fundamental tone. FIG. 12 shows a circuit example in which the circuit 22 is replaced with a diode clip circuit.

It is empirically known that the odd-order harmonic components change the perceptual effect depending on the order of the order, and if there are odd-order harmonic components in the audible band, the sharpness and the metallic feeling are low in the higher order. In the following case, the feeling of stickiness or power increases. In the present invention, a soft clip circuit is used for the circuit 22 from this rule of thumb.

The circuit 23 generates high-order even-order harmonic components from the output of the circuit 22, performs even-order harmonic component phase shift as an amplitude function of the original acoustic signal, and removes unnecessary low-frequency components.

The point A at this time outputs a waveform as shown in FIG. 16, and this spectrum has a high content of even harmonic components perceived as harmony as shown in FIG. It is possible to confirm the decrease in stickiness, the tenacity of bass, and the improvement in power.

The low-pass filter of the circuit 25 is used to sharply cut off harmonic components which are perceived as distortion from the output of the circuit 23 and are unnecessary for reproducing the beat and the missing fundamental phenomenon when the bass is emphasized. Since the circuit 27 is an inverting adder, the amplitude attenuation in the low frequency region of the original sound signal can be performed simultaneously with the addition of the harmonic component in the sound signal output of FIG.

When the original acoustic signal decreases to about 1 V at the maximum, the waveform at point A is output as shown in FIG. The asymmetric component of the waveform compared with FIG. 16 approximates in the bass region, and therefore the even harmonic component is phase-shifted as an amplitude function of the original acoustic signal, and the fundamental component is positively added in the bass region of the original acoustic signal. Amplitude enhancement can be performed.

Since this phase shift amount is 10 msec or more at a frequency of less than 40 Hz, it is perceived as an increase in volume due to the Haas effect. In addition, at frequencies where the amount of phase shift is 20 msec or more, the perception is reduced, and the phase shift operation is an amplitude function of the input signal. Is called.

FIG. 11 is a circuit in which the phase shift operation is deleted from FIG. 4. Despite almost the same basic configuration, this circuit does not improve the perceptual level due to the cocktail party effect. In order to obtain a sufficient bass emphasis effect, it is necessary to increase the amount of addition of harmonics. As in the conventional method, a sense of distortion at the time of bass emphasis and a decrease in clarity such that the phrase cannot be heard occur.

The circuit 26 is a variable resistor that adjusts the added ratio of the generated harmonic component and amplitude-controlled low-frequency component and the original acoustic signal to an optimum value, and the circuits 24 and 27 add the output of the circuit 26 and the original acoustic signal. An adder circuit is configured. Various adder circuits are conceivable, but the inversion type is used according to the legend. In the implementation of digital signal processing, the circuit 24 and the circuit 27 are unnecessary if the phase relationship is the same.

8 is a small amplitude output, FIG. 9 is a medium amplitude output, and FIG. 10 is an outline of an acoustic signal output spectrum at the time of large amplitude output. Small, medium, and large output amplitudes are expedient expressions. In actual application, it is necessary to adjust the level diagram by using the output immediately before the subsequent amplifier or speaker generates distortion as the large amplitude output.

FIGS. 5 and 6 are application examples of FIG. 1. In the circuit 28, a resistor is connected in series to a diode in the negative feedback loop of the circuit 3, and in the circuit 29, the diode of the circuit 28 is reversely connected. The circuits 28 and 29 operate as even-order harmonic generation circuits. However, by connecting a diode and a resistor in series, it becomes possible to amplify a symmetric component of the input waveform and amplify an odd-order harmonic component. .

Since the odd harmonic components amplified by the circuits 28 and 29 are perceived as sharpness or a metallic feeling, the optimum value makes the sound of the picking of the bass guitar or the skin of the bass drum clear. The connecting direction of the diode is the phase of the even harmonic component to be generated (Phase), and this phase shift amount (Shifting) is 20 msec or more in the bass region, so that it is perceived as a difference in attack feeling in the bass guitar. Then, it is possible to get a stronger attack feeling.

FIG. 18 is a circuit example of a special effect device for a distortion instrument, and the distortion and flanger are connected in series by replacing the low-pass filter of the circuit 25 with a soft clip circuit that also emphasizes the fundamental tone and generated harmonics of the low music instrument. A similar special effect is achieved.

Since high-quality bass enhancement optimized for small speakers can be realized at low cost, it can be effectively used for video game machines, mobile phones, and PC speakers. Furthermore, since the harmonic generation function according to the present invention can generate harmonic components having a strong correlation with the input waveform, the harmonic reproduction technology, outline processing to various characters and graphic data, resolution improvement technology for video signals, various waveform responses It can be applied to the future prediction of the future, demodulation of sub-Nyquist sampled signal sources, etc.

Circuits 2 and 3 can be replaced by multipliers, but they are composed of analog computing units and general-purpose components such as diodes, capacitors, and registers without using special components such as multipliers in order to realize inexpensive and simple circuits. This is an example. FIG. 2 is a block diagram showing an outline of the circuit operation of FIG. 1. This is an example of application to recording effect equipment and single-ended emphasis. It is the detail of the example of a practical circuit. It is the example of a circuit which reversed the phase of the original acoustic signal of FIG. 1, and the generation | occurrence | production harmonic signal, and added odd-order harmonic signal amplification. This is a circuit example in which odd-order harmonic signal amplification is added to FIG. It is a spectrum example of the harmonic component produced | generated by this invention. It is the acoustic signal output spectrum example 1 of FIG. It is the acoustic signal output spectrum example 2 of FIG. It is the example 3 of an acoustic signal output spectrum of FIG. 5 is a circuit example in which the phase shift operation is deleted from FIG. 4. This is a circuit example in which the circuit 22 is replaced with a diode clip circuit. This is an example of amplitude limitation by a general compressor. It is an example of amplitude limitation by a soft clip circuit. It is an example of amplitude limitation by a diode clip circuit. It is an A point waveform comparison figure with an original acoustic signal of about 3 V at maximum. It is a point A waveform comparison figure with an original sound signal of about 1 V at maximum. This is an application example to a special effect device for a distortion instrument.

Explanation of symbols

1 Phase Inversion 1 Circuit 2 Spectrum Control and Harmonic Generation 1 (Low Order Odd Harmonic Generation) Circuit 3 Differential Operation, Harmonic Generation 2 (High Order Even Order Harmonic Generation) and Low Frequency Cutoff Circuit 4 Phase Inversion 2 Circuit 5 Low frequency filtering circuit 6 Original acoustic signal, generated harmonic addition circuit 7 Block diagram notation of phase inversion 1 circuit 8 Block diagram notation of spectrum control and harmonic generation 1 (low order odd harmonic generation) circuit 9 Differential Arithmetic, harmonic generation 2 (high-order even harmonic generation) and low-frequency cutoff circuit block diagram notation 10 phase inversion 2 circuit block diagram notation 11 low-frequency filtering circuit block diagram notation 12 Original acoustic signal, generated harmonics Block diagram notation of adder circuit 13 Block diagram notation of RMS conversion circuit 14 Block diagram notation of envelope shape adjustment circuit by differential processing and integration processing 15 Spectrum of input acoustic signal by multiplication Control and harmonic generation 1 (low order odd harmonic generation) circuit block diagram representation 16 Harmonic generation 1 (low order odd harmonic generation) circuit output addition amount adjustment circuit block diagram representation 17 Differential operation and Harmonic generation 2 (high order even harmonic generation) circuit output addition adjustment and amplitude limit adjustment circuit block diagram notation 18 Harmonic generation 2 (high order even harmonic generation) circuit output low frequency cut-off frequency Block diagram notation of adjustment circuit 19 Block diagram notation of low frequency filtering and cutoff frequency adjustment circuit 20 Block diagram notation of original acoustic signal and generated harmonic addition amount adjustment circuit 21 Phase inversion 1 actual circuit 22 Spectrum control and harmonic generation 1 (Low order odd harmonic generation) Actual circuit 23 Differential operation, harmonic generation 2 (High order even harmonic generation) and low frequency cutoff actual circuit 24 Phase inversion 2 actual circuit 25 Low frequency filtration actual operation circuit 6 Generated harmonic addition ratio adjustment resistor 27 Original acoustic signal and generated harmonic addition operation circuit 28 Differential operation, inverted harmonic generation 2 (high order even harmonic generation), odd harmonic amplification and low frequency cutoff Circuit 29 Differential input, harmonic generation 2 (high order even harmonic generation), odd harmonic amplification and common input waveform for comparison to low frequency cutoff circuits 30 31, 32, 33 (40 Hz sine of about 3V maximum) wave)
31 Example of output waveform of general compressor 32 Example of output waveform by circuit 21 and circuit 22 Example of output waveform by diode clip circuit 34 Example of input waveform to FIG. 4 (up to about 3V)
35 Example of point A waveform with 34 inputs 36 Example of input waveform to Fig. 4 (up to about 1.2V)
37 Example of point A waveform with 36 inputs A Output waveform of circuit 23

Claims (17)

Add low-order odd-order harmonic signal group in the audible band of low level generated from the original acoustic signal and low-order even-order harmonic signal group in the audible band of medium to high level to the original acoustic signal, and audible band Using the beat component generated by shifting the inner low-order even-order harmonic signal group as an amplitude function of the original sound signal, it is possible to obtain a sufficient bass enhancement effect for hearing without giving excessive amplitude to the speaker diaphragm. A characteristic additional circuit and device for an audio equipment. The middle- to high-level audible in-band low-order even-order harmonic signals used in the bass emphasis process according to claim 1 are output with a phase shift operation of a maximum of 180 degrees as an amplitude function of the input signal. Audio equipment additional circuit and device to perform. Add low-order odd-order harmonic signal group in the audible band of low level generated from the original acoustic signal and low-order even-order harmonic signal group in the audible band of medium to high level to the original acoustic signal, and audible band Special effects for distortion instruments such as bass distortion and bass fuzz by adding beat components generated by phase shift of inner and lower order even harmonics as an amplitude function of the original sound signal Audio equipment additional circuit and device for realizing the device. The middle- to high-level audible in-band low-order even-order harmonic signals used in the distortion-type musical instrument special effect device according to claim 3 are output with a phase shift operation of a maximum of 180 degrees as an amplitude function of the input signal. Audio equipment additional circuit and device characterized by the above. The circuit configuration shown in FIGS. 2 and 3 is employed, and the circuit operation is an amplitude limiting circuit and an even harmonic generation circuit that generate a low order odd harmonic signal such as a soft clip circuit, a compressor circuit, or a limiter circuit. By using the harmonic signal and the original sound signal that are generated by connecting the subordinates to each other and performing the asymmetric differential operation with the original sound signal, the bass emphasis effect is achieved by bass emphasis, attenuation, and beat generation in the bass region. An audio equipment additional circuit and device characterized by that. A middle to high level audible in-band low-order even harmonic signal group used in the bass emphasis process according to claim 5 is output with a phase shift operation of 180 degrees at maximum as an amplitude function of the input signal. Audio equipment additional circuit and device to perform. Circuits 9 and 18 have a cutoff frequency of 50 Hz or less and a cutoff characteristic of 6 dB / oct. The middle- to high-level audible in-band low-order even-order harmonic signals used in the bass emphasis process according to claim 7 are output with a phase shift operation of a maximum of 180 degrees as an amplitude function of the input signal. Audio equipment additional circuit and device to perform. The circuit 11 and the circuit 19 have a cutoff frequency of 200 Hz or more and a cutoff characteristic of 24 dB / oct. The middle- to high-level audible in-band low-order even-order harmonic signals used in the bass emphasis process according to claim 9 are output with a phase shift operation of a maximum of 180 degrees as an amplitude function of the input signal. Audio equipment additional circuit and device to perform. 9. An audio equipment additional circuit and apparatus that realizes claims 5 to 8 in a digital signal processing process used for a digitized audio signal source including irreversible compression processing. The circuit configuration shown in FIGS. 5 and 6 is used, and the circuit operation is an amplitude limiting circuit and an even-order harmonic generation circuit for generating a low-order odd-order harmonic signal such as a soft clip circuit, a compressor circuit, or a limiter circuit. By using the harmonic signal and the original sound signal that are generated by connecting the subordinates to each other and performing the asymmetric differential operation with the original sound signal, the bass emphasis effect is achieved by bass emphasis, attenuation, and beat generation in the bass region. An audio equipment additional circuit and device characterized by that. The middle- to high-level audible in-band low-order even-order harmonic signals used in the bass emphasis process according to claim 12 are output with a phase shift operation of a maximum of 180 degrees as an amplitude function of the input signal. Audio equipment additional circuit and device to perform. The circuit 28 and the circuit 29 have a cut-off frequency of 50 Hz or less and a cut-off characteristic of 6 dB / oct, respectively. The circuit 8 and the circuit 15 use a voltage control resistor or a multiplier (multiplier) such as a VCA (voltage control amplifier), FET, transistor, transconductance amplifier, and optocoupler. 15. An audio equipment additional circuit and device that produces an effect equivalent to that of claims 12 to 14. 16. The acoustic equipment additional circuit and apparatus according to claim 5, wherein the order of the odd harmonic signal generated by changing the attack time and release time of the amplitude limiting operation of the circuit 8 and the circuit 15 is controlled. A recording medium on which a program for realizing the audio equipment additional circuit and apparatus according to claim 1 through digital signal processing by using an electronic computer such as a home computer or a microcomputer or a dedicated processor (DSP) is recorded.

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