JP2009071697A - Audio signal processor and audio signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal processor for simultaneously expanding upward and shifting sound image localization to the right or left with a simple circuit configuration, and to provide an audio signal processing method. <P>SOLUTION: A phase delay circuit 2 corrects amplitude and phase in a high frequency band of respective audio signals of right-left channels. A surround circuit 3 applies surround signal processing to the output signal of the phase delay circuit 2 to generate a surround signal. A balance circuit 4 adjusts gain values of surround signals of the right and left channels to generate a desired localization state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an audio signal processing apparatus and an audio signal processing method for performing signal processing for moving a sound image localization in a surround type sound field formed by speakers of two left and right channels.

  Conventionally, various techniques for freely moving sound image localization by a two-channel speaker have been proposed.

  For example, Patent Document 1 discloses a first original sound signal obtained by dividing an original sound signal of two left and right channels into a first and second original sound signal, setting a balance amount thereof, and inverting the phase. And the second original sound signal from which the in-phase component of both channels is removed and the left / right balance of the signal synthesized for each channel is made variable so that the sound image position can be set to a predetermined position in the front / rear / left / right direction. Has been.

  In Patent Document 2, panning of a sound image having a sense of breadth is performed by localizing each of a plurality of sound images generated by a musical sound signal separated into two left and right channels at predetermined positions on the front, rear, left and right sides of the listener. An apparatus capable of performing is disclosed.

Patent Document 3 discloses an apparatus that realizes upward enlargement of a sound image by performing speaker characteristic conversion by correcting the amplitude and phase of a high-frequency band for left and right channel audio signals and further performing surround signal processing. ing.
JP-A-8-47100 JP 7-87600 A JP 2006-42316 A

  In the apparatus disclosed in Patent Document 1, the sound image position can be moved back and forth and left and right, but cannot be moved up and down. In addition, the circuit scale is large and the cost performance is low.

  Also, the apparatus disclosed in Patent Document 2 can only move the sound image position to the left and right, and cannot move it in the vertical direction. Further, the configuration is fully digital, and in principle, processing by a CPU (Central Processing Unit) and a DSP (Digital Signal Processor) is used. Therefore, the circuit scale is large and complicated, and the price is high.

  In addition, the apparatus disclosed in Patent Document 3 enables the sound image to be enlarged upward, but does not mention the localization transition of the sound image in the left-right direction.

  The present invention has been made in view of the above, and an object of the present invention is to provide an audio signal processing device and an audio signal processing method capable of simultaneously realizing upward expansion of a sound image and left-right localization transition with a simple circuit configuration.

  In order to achieve the above object, the audio signal processing apparatus of the present invention performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field, the supplied left channel audio signal and right signal. An audio signal processing apparatus that performs an audio signal of a channel, amplifying an amplitude of a predetermined first high frequency band in the audio signal of the left channel and the audio signal of the right channel, and the first high frequency A first phase delay means (2) for performing correction processing for delaying the phase of the band; and a difference signal between the left channel audio signal and the right channel audio signal corrected by the first phase delay means. Filter means (R11, C3) for removing a band above a predetermined frequency in the filter, and the filter Second phase delay means (35A, 35B) for performing phase delay processing on the difference signal from which the band equal to or higher than the predetermined frequency has been removed by the stage, and the correction processing performed by the first phase delay means First mixing means (32) for mixing a left channel audio signal and the difference signal subjected to phase delay processing by the second phase delay means to generate a left channel surround signal; The right channel audio signal corrected by the phase delay means and the difference signal phase delayed by the second phase delay means are mixed to generate a right channel surround signal. A combination of the mixing means (31) and the gain value of the left channel surround signal and the gain value of the right channel surround signal is preset. So that one of the combinations of the number of gain values, characterized in that it comprises a gain adjusting means for adjusting (4) the gain value of the surround signal and a surround signal of the right channel of the left channel.

  Also, the audio signal processing apparatus of the present invention performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on the supplied left channel audio signal and right channel audio signal. An audio signal processing apparatus for amplifying a predetermined first high frequency band amplitude in the left channel audio signal and the right channel audio signal, and delaying the phase of the first high frequency band The first phase delay means (2) for performing the correction processing, and the sum signal of the left channel audio signal and the right channel audio signal corrected by the first phase delay means A mid-range correction filter means (34) for performing a band correction process and a correction process by the first phase delay means. Filter means (R11, C3) for removing a band of a predetermined frequency or higher in the difference signal between the left channel audio signal and the right channel audio signal, and a band of the predetermined frequency or higher by the filter means. Second phase delay means (35A, 35B) for performing phase delay processing on the removed difference signal, the left channel audio signal corrected by the first phase delay means, and the mid-range First mixing means (32) for generating a left channel surround signal by mixing the sum signal corrected by the correction filter means and the difference signal phase-delayed by the second phase delay means. ), The right-channel audio signal corrected by the first phase delay means, and the mid-range correction filter A second mixing unit (31) that mixes the sum signal corrected by step (b) and the difference signal phase-delayed by the second phase delay unit to generate a right channel surround signal; The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And a gain adjusting means (4) for adjusting a gain value of the surround signal of the right channel, and a predetermined second in the first high frequency band in the surround signal of the left channel and the surround signal of the right channel. Attenuating means (C6, C7) for attenuating the high frequency band is provided.

  Further, the first phase delay means according to the audio signal processing device of the present invention amplifies the amplitude of the first high frequency band in the left channel audio signal and the right channel audio signal, and The first high frequency in the left channel audio signal and the right channel audio signal amplified and delayed by the predetermined phase delay amount after the phase of the high frequency band is delayed by a predetermined phase delay amount It is a means for further delaying the phase of the band.

  Also, the audio signal processing method of the present invention performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on the supplied left channel audio signal and right channel audio signal. An audio signal processing method performed on the left channel audio signal and the right channel audio signal for amplifying a predetermined first high frequency band amplitude and changing the phase of the first high frequency band. A correction step for performing a delaying correction process; a step of removing a band of a predetermined frequency or higher in a difference signal between the left channel audio signal and the right channel audio signal corrected in the correction step; Phase difference with respect to the difference signal from which the frequency band above A left-channel surround signal is generated by mixing a phase delay step for processing, the left channel audio signal corrected in the correction step, and the difference signal phase-delayed in the phase delay step. Mixing the right channel audio signal corrected in the correction step and the difference signal phase delayed in the phase delay step to generate a right channel surround signal; The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And adjusting the gain value of the right channel surround signal; Characterized in that it contains.

  Also, the audio signal processing method of the present invention performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on the supplied left channel audio signal and right channel audio signal. An audio signal processing method performed on the left channel audio signal and the right channel audio signal for amplifying a predetermined first high frequency band amplitude and changing the phase of the first high frequency band. A correction step for performing a delay correction process, and a mid-range correction step for performing a correction process for a voice band on the sum signal of the left channel audio signal and the right channel audio signal corrected in the correction step. And the audio of the left channel corrected in the correction step. A step of removing a band of a predetermined frequency or higher in a difference signal between the signal and the audio signal of the right channel, and a phase delay step of performing a phase delay process on the difference signal from which the band of the predetermined frequency or higher is removed And the left channel audio signal corrected in the correction step, the sum signal corrected in the midrange correction step, and the difference signal phase delayed in the phase delay step. Generating a left channel surround signal, the right channel audio signal corrected in the correction step, the sum signal corrected in the midrange correction step, and a phase in the phase delay step. Mixing the delayed difference signal to generate a right channel surround signal; The left channel surround signal and the left channel surround signal so that the combination of the gain value of the left channel surround signal and the gain value of the right channel surround signal is one of a plurality of preset gain value combinations. Adjusting the gain value of the right channel surround signal and attenuating a predetermined second high frequency band within the first high frequency band in the left channel surround signal and the right channel surround signal; It is characterized by including.

  Further, the correction step according to the audio signal processing method of the present invention amplifies the amplitude of the first high frequency band in the left channel audio signal and the right channel audio signal, and the first high frequency The phase of the first high frequency band in the left channel audio signal and the right channel audio signal amplified and phase delayed by the predetermined phase delay amount after delaying the phase of the band by a predetermined phase delay amount Is a step of further delaying.

  According to the present invention, the upward expansion of the sound image and the left-right localization transition can be realized simultaneously with a simple circuit configuration.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  First, considerations regarding the focus and sound image localization transition of the present invention will be described in detail.

(A) Virtual sound source formation by speaker characteristic conversion A general full-range speaker used in a relatively low-priced left and right two-channel stereo playback device includes a simulation diagram of amplitude characteristics and phase characteristics shown in FIG. As can be seen from the simulation diagram of the impedance characteristic and the phase characteristic shown in FIG. 2, the high frequency reproduction limit is low, the phase advances as the frequency increases, and the impedance increases as the frequency increases.

  On the other hand, as can be seen from the simulation diagram of the amplitude characteristic and phase characteristic of the 2-way speaker shown in FIG. 3, although the high-frequency reproduction limit of the 2-way speaker used in the high-class stereo reproduction apparatus is high, the phase characteristic is woofer and tweeter. Before and after the crossover point, it changes greatly due to the influence of the network circuit, and further delays as the frequency increases.

  As described above, the static characteristics of the full-range speaker and the 2-way speaker have their respective disadvantages, and the ideal high-frequency reproduction limit as shown in FIG. 4 is 20 kHz or more and the phase characteristics are flat over the entire area. The actual situation is that the amplitude characteristics and phase characteristics of the speaker system are greatly different.

  In general theory, it is said that human hearing is easy to capture directivity in a high frequency band of 1 kHz or higher, and conversely, directivity is difficult to recognize in a low frequency band. In other words, the 2-way speaker has a wider reproduction band and wider directivity than a full-range speaker, and is easily recognized by human hearing.

  Focusing on this point, the characteristics and characteristics of the ideal speaker system are simulated by converting the amplitude and phase of the full-range speaker at the same time (in other words, improving the phase advance caused by the voice coil of the speaker and increasing the upward direction). If possible, it is possible to improve the sound quality and expand the sound image.

  That is, by performing speaker characteristic conversion (high frequency band phase shift and amplification correction), the high frequency reproduction limit of the full range speaker is extended upward, and the phase characteristic is flattened, so that the high frequency band is This will improve the time gap of the sound and will produce a reproduced sound close to the original sound.

  5A and 5B are conceptual diagrams of an enlarged sound source by speaker characteristic conversion. FIG. 5A is a diagram viewed from the front of the speaker, and FIG. 5B is a diagram viewed from the side of the speaker. As a result of the characteristic conversion of the speakers, the sound source reproduction area in the middle and high frequency band is expanded, and as a result, as shown in FIG. 5, the expansion of the sound image as a whole (expanded sound source) is expected.

  Next, the expansion sound source is considered in consideration of the influence of the installation surface such as the floor surface, which is a general use state. 6A and 6B are conceptual diagrams of an enlarged sound source by speaker characteristic conversion when the speaker is installed on a flat surface. FIG. 6A is a diagram seen from the front of the speaker, and FIG. 6B is a diagram seen from the side of the speaker. FIG.

  In general, energy is enhanced in the low frequency band because the installation surface has a high reflectance, but the high frequency band is absorbed by the installation surface in the opposite manner, and the energy often decreases. In other words, when the speaker is installed on a flat desk or floor, as shown in FIG. 6, the expanded sound source does not expand downward but expands in the other direction to synthesize the entire spectrum. The center of the virtual sound source is now shifted upward. Therefore, if these phenomena are perceived by human auditory sense, the entire sound image can be felt by being localized in the upward direction. This is because a virtual sound source is created by recognizing a high frequency band by hearing.

(B) Formation of sound image upward enlargement using a surround circuit The enlarged sound source / virtual sound source by the speaker characteristic conversion in the above (a) is considered as a (2-channel) stereo sound source.

  FIG. 7 is a conceptual diagram of changes in the sound source center and sound source reproduction range of the front left and right speakers as viewed from the listener. As shown in FIG. 7, in the case of a stereo sound source (L / R channel), when the reproduction range is expanded by speaker characteristic conversion, the left and right channels are close to each other and the stereo feeling is reduced. Become. As a means for solving this, a surround circuit is considered suitable. This is because, as can be seen from FIG. 7, the virtual sound source after the surround signal processing spreads to the left and right positions, and the LR difference (distance between the sound sources) of the expanded sound source increases.

  From FIG. 7, it can be seen that the left and right virtual sound sources that give an effective stereo effect to the outside upward direction of the original sound source are formed as a result of the above-described speaker characteristic conversion and surround signal processing. The above is one purpose of using the surround circuit.

  Next, the mechanism of sound image localization in space is considered based on human hearing.

FIG. 8 is a schematic diagram showing the mechanism of sound image localization in space as a vector. In FIG. 8, the original sound L / R is a stereo sound source. If the time difference between both ears of the dummy head M is Δt1, the left and right surround signals can be expressed as L + Δt1 (LR), R + Δt1 (LR). When the upward shift distance is Δd2, the correlation can be expressed by the following (Formula 1) to (Formula 4).

  Here, θ1 is a phase angle generated when the original sound L / R is shifted by Δd2, and θ2 is a case where the surround signals L + Δt1 (LR) and R + Δt1 (LR) are further shifted upward by Δd2. The phase angle generated in

Further, when Δt2 transition is performed with the localization direction of the original sound L / R as a time difference in the right direction and Δt3 is a time difference when the surround signal is shifted at the same localization ratio, the correlation is expressed by the following (Equation 5) to (Expression 9)

  Here, θ3 is a phase angle generated when the localization direction of the original sound L / R is shifted Δt2 to the right, and θ4 is a phase angle generated when the localization direction of the surround signal is shifted Δt3 to the right.

  From the above (Formula 5) to (Formula 7), it is possible to realize a localization transition for a longer time when the surround signal processing is performed than when the surround signal processing is not performed. That is, it becomes easy to be recognized by human hearing. Further, from (Equation 7), since θ3 and θ4 are different values, a sound quality that is less susceptible to ear interference and less uncomfortable is obtained audibly. All of these are applied when the localization of the original sound and the localization processed by the surround signal are in a proportional relationship as shown in (Formula 8).

  As described above, the signal enlarged above the sound image is subjected to surround signal processing, so that a desired left-right localization transition can be easily performed and maintained without impairing the sound quality. Further, by selecting the upward shift distance Δd2 as a desired upward enlargement and adjusting the left / right localization transition time difference Δt3, optimal sound image localization can be performed.

  From the above considerations, in order to perform effective sound image upward enlargement and left-right localization transition, it is important to combine the phase delay circuit, surround circuit, and balance circuit for performing the above-mentioned speaker characteristic conversion. is there.

  Therefore, as shown in FIG. 9, the audio signal processing device 1 according to the embodiment of the present invention is a phase that simultaneously performs amplitude correction and phase correction of the first high frequency band for the audio signals of the left and right channels. A delay circuit 2; a surround circuit 3 that performs surround signal processing on the output signal of the phase delay circuit 2 to generate a surround signal for the left and right channels; a balance circuit 4 that adjusts the gain of the surround signal for the left and right channels; The circuit configuration includes a control circuit 5 that controls each of the components.

  The phase delay circuit 2 includes a right channel phase delay circuit 21A and a left channel phase delay circuit 21B.

  The right-channel phase delay circuit 21A includes an operational amplifier 22, and a non-inverting input terminal and an inverting input terminal receive a right-channel audio signal from an audio signal source (not shown) via resistors R1 and R2. Is done. A capacitor C1 is connected to the non-inverting input terminal of the operational amplifier 22, and a grounded emitter transistor Q1 is connected between the capacitor C1 and the ground. A feedback resistor R3 is connected between the inverting input terminal and the output terminal of the operational amplifier 22.

  Thus, the right channel phase delay circuit 21A is configured by connecting the inverter circuit composed of the operational amplifier 22 and the resistors R1 to R3 and the filter circuit composed of the capacitor C1 and the resistor R1. The base of the transistor Q1 is connected to the control circuit 5. The transistor Q1 is turned on and off by a control signal CTL1 from the control circuit 5, so that the connection and unconnection of the capacitor C1 can be switched. .

  Similarly, the left channel phase delay circuit 21B includes an inverter circuit including an operational amplifier 23 and resistors R4 to R6, a filter circuit including a capacitor C2 and a resistor R4, and a transistor Q2. The transistor Q2 is turned on and off by the control signal CTL1 supplied to the capacitor C2, so that the connection and disconnection of the capacitor C2 can be switched.

  The surround circuit 3 includes operational amplifiers 31 to 33, a mid-range correction filter circuit 34, and phase delay devices 35A and 35B. The non-inverting input terminal of the operational amplifier 31 is connected to the output terminal of the operational amplifier 22 of the right channel phase delay circuit 21A. The non-inverting input terminal of the operational amplifier 32 is connected to the output terminal of the operational amplifier 23 of the left channel phase delay circuit 21B.

  The output terminals of the operational amplifiers 22 and 23 are connected to each other through resistors R7 and R8, and the midpoint of connection is connected to a mid-range correction filter circuit 34 that corrects the audio band. The output end of the mid-range correction filter circuit 34 is connected to the non-inverting input terminals of the operational amplifiers 31 and 32 via resistors R12 and R13. A switch SW1 is provided at the output end of the mid-range correction filter circuit 34, and is configured to be switched between connected and unconnected under the control of the control circuit 5.

  The non-inverting input terminal of the operational amplifier 33 is connected to the output terminal of the operational amplifier 22 of the right channel phase delay circuit 21A via the resistor R9, and the inverting input terminal is connected to the operational amplifier of the left channel phase delay circuit 21B via the resistor R10. 23 output terminals.

  The output terminal of the operational amplifier 33 is connected to a two-stage phase delay device 35A, 35B via a resistor R11, and a capacitor C3 is connected between the input terminal of the phase delay device 35A and the ground. The resistor R11 and the capacitor C3 constitute a CR filter for removing a band of a predetermined frequency or higher. Further, phase delay amount adjusting capacitors C4 and C5 are connected to the phase delay devices 35A and 35B, respectively.

  The output terminal of the phase delay device 35B is connected to the non-inverting input terminal of the operational amplifier 31 via the resistor R14, and is connected to the inverting input terminal of the operational amplifier 32 via the resistor R15. The output terminals of the operational amplifiers 31 and 32 are connected to the respective inverting input terminals. A switch SW2 is provided at the output terminal of the phase delay device 35B, and can be switched between connected and unconnected under the control of the control circuit 5.

  The output terminals of the operational amplifiers 31 and 32 are connected to the balance circuit 4. In the balance circuit 4, a series circuit including a resistor R 17, a capacitor C 6, and a transistor Q 3, a series circuit including a resistor R 18 and a transistor Q 4, and a resistor R 19 are connected in parallel to an output terminal of the operational amplifier 31 via a resistor R 16. And the emitters of the transistors Q3 and Q4 and one end of the resistor R19 are grounded.

  Similarly, a series circuit including a resistor R21, a capacitor C7, and a transistor Q5, a series circuit including a resistor R22 and a transistor Q6, and a resistor R23 are connected in parallel to the output terminal of the operational amplifier 32 through a resistor R20. The emitters of the transistors Q5 and Q6 and one end of the resistor R23 are grounded.

  The bases of the transistors Q3 to Q6 are connected to the control circuit 5. By turning the transistors Q3 to Q6 on and off by the control signals CTL2 to CTL5 from the control circuit 5, resistors R17, 18, 21, 22 and a capacitor The connection between C6 and C7 can be switched. When the H level signal is input as the control signals CTL2 to CTL5, the transistors Q3 to Q6 are turned on, and when the L level signal is input, the transistors Q3 to Q6 are turned off.

  In the audio signal processing apparatus 1 described above, the purpose of the phase delay circuit 2 is to perform amplitude correction and phase correction of the first high frequency band (for example, about 1 to 100 kHz) for forming the virtual sound source described above. To do at the same time.

  In this regard, in the conventional method, the amplitude correction is performed by the equalizer circuit and the phase is corrected by the phase delay circuit. However, in this method, the phase also changes in the equalizer. It has been difficult to correct it with a circuit and perform a desired phase delay.

  In the audio signal processing apparatus 1 according to the present embodiment, the phase delay circuit 2 is implemented by a single circuit stage in order to improve characteristics, reduce the number of circuit stages, and prevent deterioration in sound quality.

  As described above, the phase of a general full-range speaker advances due to the influence of the inductive component of the voice coil as the frequency increases. By performing amplitude correction and phase correction on this, it is possible to reproduce an ideal speaker system.

  In the right channel phase delay circuit 21A, when the value of the resistor R2 is set to a value smaller than the resistor R3, the transfer function G1 is as follows.

When the frequency F is from 0 to the cutoff frequency determined by Fc = 1 / 2π · C1 · R1, the transfer function G1 is expressed by the following (Equation 10). This circuit functions as an all-pass filter, and G1 = 1. It is fixed. Further, the phase in this band does not change.

In the band where the frequency F is equal to or higher than the cut-off frequency of Fc = 1 / 2π · C1 · R1, the impedance of the capacitor C1 decreases. Therefore, the circuit functions as an inverting amplifier circuit, and the transfer function G1 is expressed by the following (Equation 11). Is done.

  That is, the amplitude characteristic changes with Fc = 1 / 2π · C1 · R1 as an inflection point. Further, from the above (Equation 12), by appropriately setting the values of the resistor R1 and the capacitor C1, the delay amount of the phase θ can be adjusted in the range of 0 to −180 °.

  In this way, a desired phase delay amount and amplification degree can be obtained for the target speaker, set size, etc. by appropriate selection of the circuit constants R1, R2, R3, C1 of the right channel phase delay circuit 21A. Can be set. In the above description, the phase delay circuit 21A for the right channel has been described. Similarly, the phase delay circuit 21B for the left channel can be set to a desired phase delay amount by appropriately selecting the circuit constants R4, R5, R6, and C2. The degree of amplification can be set.

  For example, if the circuit constants of the phase delay circuit 21A for the right channel are R1 = 10 kΩ, R2 = 4.7 kΩ, R3 = 10 kΩ, and C1 = 0.0047 μF, Fc = 3383 Hz. FIG. 10 shows a change in static characteristics when the sound quality correction of the full range speaker is performed using this circuit. Comparing FIG. 10 with FIG. 3 representing the characteristics of the ideal speaker system, it can be seen that the characteristics of the full range speaker corrected by the right channel phase delay circuit 21A approximate the characteristics of the ideal speaker. That is, the amplitude of the high frequency band that is lacking in the full range speaker is compensated, and at the same time, the phase advance in the middle and high frequency band is improved, so that a reproduced sound close to the original sound can be obtained.

  Of course, only the phase delay circuit 2 does not realize the sound image upward enlargement and left-right localization transition, which are the main focus of the present invention, but the surround circuit 3 and the balance circuit 4 are connected to the phase delay circuit 2 as shown in FIG. Thus, the present invention is established.

  As described above, there are two purposes for using the surround circuit 3. One purpose is to expand the sound field and the localization transition effect, and the other purpose is to enable upward expansion of the sound image with a small amount of phase delay by left and right expansion of the sound field. The purpose of using the balance circuit 4 is to perform localization control by varying the left and right signal levels and to give different frequency characteristics to the left and right signals.

  In the surround circuit 3, first, the signals R and L that have passed through the right channel phase delay circuit 21A and the left channel phase delay circuit 21B in the previous stage are each divided into three signals. One is directly input to the non-inverting input terminals of the operational amplifiers 31 and 32 at the subsequent stage. The other is input to the operational amplifier 33 of the circuit for generating the difference signal (R−L) of R and L. Here, a band of a predetermined frequency or higher (for example, about 10 kHz or higher) is removed from the difference signal (R−L) by a CR filter including the resistor R11 and the capacitor C3. As a result, the band that has been corrected by the right channel phase delay circuit 21A and the left channel phase delay circuit 21B and has become excessively high and unnecessary is removed. Further, the difference signal (R−L) from which the band equal to or higher than the predetermined frequency has been removed passes through the two-stage phase delay devices 35A and 35B and is added to the subsequent operational amplifiers 31 and 32, respectively.

  Further, the other signal is a sum signal (L + R) of L and R, which is input to the mid-range correction filter circuit 34 and corrects the voice band that is lost by the surround circuit 3.

  In the operational amplifier 31, the signal R from the phase delay circuit 21A for the right channel, the sum signal (L + R) corrected by the mid-range correction filter circuit 34, and the difference signal (RL) that has passed through the phase delay devices 35A and 35B. Are mixed and input to the balance circuit 4 as a surround signal for the right channel. Further, in the operational amplifier 32, the signal L from the phase delay circuit 21B for the left channel, the sum signal (L + R) corrected by the mid-range correction filter circuit 34, and the difference signal (R−) passing through the phase delay devices 35A and 35B. L) is mixed and becomes a surround signal of the left channel and is input to the balance circuit 4.

  The balance circuit 4 is provided with two control terminals on the left and right sides. By turning on and off the transistors Q3 to Q6 by the control signals CTL2 to CTL5, the gain can be set in four steps independently on the left and right.

  As described above, the audio signal processing apparatus 1 according to the present embodiment is configured with a simple minimum analog circuit in order to simplify the circuit configuration. Further, the transistors Q1 and Q2 provided in the phase delay circuit 2 can be selected to enlarge the sound image upward. That is, if the capacitors C1 and C2 are not connected, the operational amplifiers 22 and 23 simply function as buffer amplifiers, and no signal change occurs. In addition, the use of the mid-range correction filter circuit 34 and selection of non-use can be made by setting the switch SW1 according to conditions such as the arrangement and structure of the use set. Similarly, whether the surround function is used or not can be selected by setting the switch SW2.

Here, the left and right channel output signals Lo and Ro obtained by the audio signal processing apparatus 1 shown in FIG. 9 can be expressed by the following (Expression 13) to (Expression 16). G1 is the transfer function of the preceding phase delay circuit 2, G2 is the transfer function of the right channel of the balance circuit 4, G3 is the transfer function of the left channel of the balance circuit 4, Δt is the phase delay amount of the surround circuit 3, and K is This is the mid-range correction coefficient.

  The first term of the above (Formula 13) and (Formula 14) indicates that the left and right signals L and R are converted by the phase delay circuit 2 with the transfer function G1. Further, gain conversion is performed by the transfer functions G2 and G3. As a result, the original sounds L and R are amplified in amplitude and phase-delayed by the transfer function G1 of the above (Formula 11).

  Similarly, the second term indicates that the surround difference signal component (L−R) or (R−L) is signal-converted by the phase delay circuit 2 with the transfer function G1. As a result, amplitude amplification and phase delay are also performed for the difference signal component (LR) or (RL) which is an indirect sound. Further, it can be seen that the indirect sound is also subjected to gain conversion by the transfer functions G2 and G3 to determine the left and right localization.

  Similarly, for the third term, it is understood that the midrange correction component is signal-converted by the transfer function G1 by the phase delay circuit 2 and further gain-converted by the transfer functions G2 and G3 to determine the left and right localization.

  As a result of these signal processings, the amplitude of the first high frequency band increases, the phase advance is improved and flattened, and the sound field is expanded in the left-right direction. Therefore, the virtual sound source SL2, shown in FIG. SR2 is formed, and the localization is determined by its level.

  On the other hand, the left and right control terminals of the balance circuit 4 can shift left and right by the active control. What is characteristic here is that the balance circuit 4 includes capacitors C6 and C7 connected in series to the resistors R17 and R21.

  Even when the capacitors C6 and C7 are not provided in the balance circuit 4, the transition of the left and right localization can be realized by setting the balance of the surround signals of the left and right channels. However, by providing the capacitors C6 and C7, the balance circuit 4 is simple. In addition to setting the balance of the surround signals of the left and right channels, the second delay, which is an unnecessary frequency band within the first high frequency band, increases too much in the phase delay circuit 2 when the gain is attenuated. An operation of attenuating a frequency band (for example, about 5 to 100 kHz) is performed. This can be seen from (Equation 15) and (Equation 16). By attenuating only the unnecessary second high frequency band, level control is possible without dropping the mid-tone band, which is the voice band, and a left-right localization transition is realized without causing unnatural sound quality changes. be able to.

  In addition, the balance circuit 4 is not only used as an attenuator, but also used as a left / right gain variable circuit. That is, a desired localization state is created by combining the maximum attenuation and the minimum attenuation with the center localization as the center of the attenuation. For example, when the right direction localization is maximum, the gain of the right channel is maximum and the gain of the left channel is minimum. In center localization, the gain of each channel is the same and is an intermediate gain.

  As an example, in the balance circuit 4 of FIG. 9, the localization state and gain setting when R16 = R20 = 6.8 kΩ, R17 = R18 = 10 kΩ, R19 = 100 kΩ, R21 = R22 = 10 kΩ, and R23 = 100 kΩ are shown in FIG. Shown in

  In this case, three levels of gain settings (−0.57 dB, −4.8 dB, and −7.7 dB) are independently performed on the left and right sides by combining the H and L level signals in the control signals CTL2 to CTL5 as shown in FIG. Furthermore, sound image localization control in five stages (maximum right direction localization to maximum left direction localization) can be performed from these combinations. For example, when the control signals CTL2 and CTL3 are L level signals and the control signals CTL4 and CTL5 are H level signals, the right channel gain is maximum (−0.57 dB) and the left channel gain is minimum (−7.7 dB). And the right direction localization is maximum.

Next, simulation diagrams of amplitude characteristics and phase characteristics of the output signal obtained by the audio signal processing apparatus 1 shown in FIG. 9 are shown in FIGS. FIG. 12 is a simulation diagram of the amplitude characteristic and phase characteristic of the right channel output signal R ₀ when CTL 3 is an L level signal, and FIG. 13 is an amplitude characteristic of the right channel output signal R ₀ when CTL 3 is an H level signal. It is a simulation figure of a phase characteristic. 12 and 13, it can be seen that the amplitude characteristic rises with the valley of the surround as an inflection point. Further, in FIG. 13, it can be seen that the increase in the amplitude characteristic reaches a peak due to the influence of the capacitor C6, particularly in the high frequency band of 10 kHz or more, compared to FIG.

  Depending on the distance between the left and right speakers or the enclosure size of the two-channel audio system, there may be a case where the phase delay amount is insufficient in the configuration having only one stage of the phase delay circuit 2 such as the audio signal processing device 1 of FIG. In such a case, as shown in FIG. 14, the phase delay circuit 2A having the same configuration as that of the phase delay circuit 2 is connected in series so that a maximum phase delay amount of -360 ° can be obtained. Is desirable.

  In the audio signal processing apparatus shown in FIG. 14, the phase delay circuit 2 </ b> A further applies the left and right channel audio signals subjected to the amplitude correction of the first high frequency band and the −180 ° phase delay process by the phase delay circuit 2. By performing the phase delay processing of the first high frequency band, a phase delay amount of up to −360 ° can be obtained. As a result, a desired sound image can be enlarged upward.

  Further, in the audio signal processing device 1 of FIG. 9, the case where the left and right control terminals of the balance circuit 4 are two is shown, but more control terminals may be provided. For example, by using a balance circuit 4A having four control terminals on the left and right as shown in FIG.

  In the balance circuit 4A, a series circuit including a resistor R25, a capacitor C8, and a transistor Q7, and a series including a resistor R26, a capacitor C9, and a transistor Q8 are connected to the output terminal of the operational amplifier 31 of the surround circuit 3 via a resistor R24. A circuit, a series circuit composed of a resistor R27 and a transistor Q9, a series circuit composed of a resistor R28 and a transistor Q10, and a resistor R29 are connected in parallel, and the emitters of the transistors Q7 to Q10 and one end of the resistor R29 are grounded. .

  Similarly, a series circuit including a resistor R31, a capacitor C10, and a transistor Q11 and a series circuit including a resistor R32, a capacitor C11, and a transistor Q12 are connected to the output terminal of the operational amplifier 32 of the surround circuit 3 via a resistor R20. A series circuit composed of a resistor R33 and a transistor Q13, a series circuit composed of a resistor R34 and a transistor Q14, and a resistor R35 are connected in parallel, and the emitters of the transistors Q11 to Q14 and one end of the resistor R35 are grounded.

  The bases of the transistors Q7 to Q14 are connected to the control circuit 5. By turning the transistors Q7 to Q14 on and off by the control signals CTL6 to CTL13 from the control circuit 5, resistors R25 to R28, R31 to R34, and capacitors The connection between C8 to C11 and non-connection can be switched. Here, when the H level signal is input as the control signals CTL6 to CTL13, the transistors Q7 to Q14 are turned on, and when the L level signal is input, the transistors Q7 to Q14 are turned off.

  In such a balance circuit 4A, when R24 = R30 = 6.8 kΩ, R25 = R26 = R27 = 15 kΩ, R28 = 10 kΩ, R29 = 100 kΩ, R26 = R27 = R28 = 15 kΩ, R34 = 10 kΩ, R35 = 100 kΩ FIG. 16 shows the localization state and gain setting. Further, FIG. 17A shows an image of vertical sound image localization transition, and FIG. 17B shows an image of horizontal sound image localization transition.

In this case, six levels of gain settings (−0.5 dB, −2.5 dB, −4.8 dB, and left and right independent, respectively) by the combination of the H and L level signals in the control signals CTL6 to CTL13 as shown in FIG. −7 dB, −8.5 dB, −9.7 dB), and from these combinations, seven steps (rightward localization maximum (R _max )) as shown in FIGS. 16, 17 (a), (b) Sound image localization control with a maximum leftward localization (L _max ) can be performed.

  As described above, according to the present embodiment, the phase delay circuit 2 performs amplitude correction and phase correction of the first high frequency band on the audio signals of the left and right channels, and the output signal of the phase delay circuit 2 The surround circuit 3 is subjected to surround signal processing, and the balance circuit 4 is used to adjust the gains of the surround signals of the left and right channels. For example, as shown in FIGS. A clear left and right localization transition can be realized simultaneously.

  For this reason, even when there is only a place where a speaker is installed, such as the floor of the corner of the room, the optimal listening state can be obtained by localizing the sound image to a desired position. It becomes possible.

  In addition, the circuit system of the audio signal processing apparatus 1 of the present embodiment is analog, and the circuit can be realized with a simple circuit configuration. For this reason, there also exists an advantage that it is excellent in cost performance.

It is a simulation figure of the amplitude characteristic and phase characteristic of a full range speaker. It is a simulation figure of the impedance characteristic and phase characteristic of a full range speaker. It is a simulation figure of the amplitude characteristic and phase characteristic of a 2-way speaker. It is a figure of the amplitude characteristic and phase characteristic of an ideal speaker system. It is the conceptual diagram of the expansion sound source by speaker characteristic conversion, (a) is the figure seen from the front of a speaker, (b) is the figure seen from the side of the speaker. It is the conceptual diagram of the expansion sound source by speaker characteristic conversion at the time of installing a speaker in a plane, (a) is the figure seen from the front of a speaker, (b) is the figure seen from the side of the speaker. It is a conceptual diagram of the change of the sound source center and sound source reproduction range of the front left and right speakers viewed from the listener. It is the schematic diagram which represented the mechanism of the sound image localization in space with the vector. 1 is a circuit diagram of an audio signal processing device according to an embodiment of the present invention. It is a simulation figure which shows the amplitude characteristic and phase characteristic of a full-range speaker showing the improvement effect of the characteristic conversion by a phase delay circuit. FIG. 10 is a table showing an example of a combination of left and right localization in the audio signal processing device shown in FIG. 9. FIG. 10 is a simulation diagram illustrating an example of amplitude characteristics and phase characteristics of an output signal obtained by the audio signal processing device illustrated in FIG. 9. FIG. 10 is a simulation diagram illustrating another example of an amplitude characteristic and a phase characteristic of an output signal obtained by the audio signal processing device illustrated in FIG. 9. It is a block diagram which shows the audio signal processing apparatus which connected the phase delay circuit in two steps. It is a circuit diagram of a balance circuit having four control terminals on the left and right. FIG. 16 is a table showing an example of a combination of left and right localization in the audio signal processing apparatus using the balance circuit shown in FIG. 15. (A) is a figure which shows the image of the sound image localization transition of a perpendicular direction, (b) is a figure which shows the image of the sound image localization transition of a horizontal direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Audio signal processing device 2, 2A Phase delay circuit 3 Surround circuit 4, 4A Balance circuit 5 Control circuit 21A Right channel phase delay circuit 21B Left channel phase delay circuit 22, 23, 31-33 Operational amplifier 34 Middle sound range correction filter circuit 35A, 35B phase delay

Claims (6)

An audio signal processing apparatus that performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on a supplied left channel audio signal and right channel audio signal,
First phase delay means for amplifying the amplitude of a predetermined first high frequency band in the left channel audio signal and the right channel audio signal and performing a correction process for delaying the phase of the first high frequency band When,
Filter means for removing a band of a predetermined frequency or higher in a difference signal between the left channel audio signal and the right channel audio signal corrected by the first phase delay means;
Second phase delay means for performing phase delay processing on the difference signal from which the band equal to or higher than the predetermined frequency has been removed by the filter means;
The left channel audio signal corrected by the first phase delay means and the difference signal phase delayed by the second phase delay means are mixed to generate a left channel surround signal. First mixing means;
The right channel audio signal corrected by the first phase delay means and the difference signal phase delayed by the second phase delay means are mixed to generate a right channel surround signal. A second mixing means;
The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And an audio signal processing device comprising: gain adjusting means for adjusting a gain value of the surround signal of the right channel. An audio signal processing apparatus that performs signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on a supplied left channel audio signal and right channel audio signal,
First phase delay means for amplifying the amplitude of a predetermined first high frequency band in the left channel audio signal and the right channel audio signal and performing a correction process for delaying the phase of the first high frequency band When,
A mid-range correction filter means for performing an audio band correction process on the sum signal of the left channel audio signal and the right channel audio signal corrected by the first phase delay means;
Filter means for removing a band of a predetermined frequency or higher in a difference signal between the left channel audio signal and the right channel audio signal corrected by the first phase delay means;
Second phase delay means for performing phase delay processing on the difference signal from which the band equal to or higher than the predetermined frequency has been removed by the filter means;
The left channel audio signal corrected by the first phase delay means, the sum signal corrected by the mid-range correction filter means, and the phase delay processed by the second phase delay means First mixing means for mixing the difference signal to generate a left channel surround signal;
The right channel audio signal corrected by the first phase delay means, the sum signal corrected by the mid-range correction filter means, and the phase delay processed by the second phase delay means A second mixing means for mixing the difference signal and generating a right channel surround signal;
The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And gain adjusting means for adjusting the gain value of the surround signal of the right channel;
An audio signal processing apparatus comprising: attenuation means for attenuating a predetermined second high frequency band in the first high frequency band in the left channel surround signal and the right channel surround signal.   The first phase delay means amplifies the amplitude of the first high frequency band in the left channel audio signal and the right channel audio signal, and the phase of the first high frequency band is a predetermined phase delay. Means for further delaying the phase of the first high frequency band in the left channel audio signal and the right channel audio signal amplified and delayed by the predetermined phase delay amount after being delayed by an amount. The audio signal processing apparatus according to claim 1, wherein the audio signal processing apparatus is an audio signal processing apparatus. An audio signal processing method for performing signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on a supplied left channel audio signal and right channel audio signal,
A correction step of amplifying the amplitude of a predetermined first high frequency band in the left channel audio signal and the right channel audio signal and performing a correction process of delaying the phase of the first high frequency band;
Removing a band of a predetermined frequency or higher in a difference signal between the left channel audio signal and the right channel audio signal corrected in the correction step;
A phase delay step for performing a phase delay process on the difference signal from which the band equal to or higher than the predetermined frequency has been removed;
Mixing the left channel audio signal corrected in the correction step and the difference signal phase delayed in the phase delay step to generate a left channel surround signal;
Mixing the right channel audio signal corrected in the correction step and the difference signal phase delayed in the phase delay step to generate a right channel surround signal;
The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And adjusting the gain value of the right channel surround signal. An audio signal processing method for performing signal processing for obtaining a surround signal to be reproduced by a speaker to create a surround sound field on a supplied left channel audio signal and right channel audio signal,
A correction step of amplifying the amplitude of a predetermined first high frequency band in the left channel audio signal and the right channel audio signal and performing a correction process of delaying the phase of the first high frequency band;
A mid-range correction step of performing a correction process of a voice band on the sum signal of the left channel audio signal and the right channel audio signal corrected in the correction step;
Removing a band of a predetermined frequency or higher in a difference signal between the left channel audio signal and the right channel audio signal corrected in the correction step;
A phase delay step for performing a phase delay process on the difference signal from which the band equal to or higher than the predetermined frequency has been removed;
Mixing the left channel audio signal corrected in the correction step, the sum signal corrected in the midrange correction step, and the difference signal phase delayed in the phase delay step, Generating a surround signal for the left channel;
Mixing the right channel audio signal corrected in the correction step, the sum signal corrected in the midrange correction step, and the difference signal phase delayed in the phase delay step, Generating a right channel surround signal;
The left channel surround signal so that the combination of the left channel surround signal gain value and the right channel surround signal gain value is one of a plurality of preset gain value combinations. And adjusting the gain value of the right channel surround signal and attenuating a predetermined second high frequency band within the first high frequency band in the left channel surround signal and the right channel surround signal. An audio signal processing method comprising the steps of: The correcting step amplifies the amplitude of the first high frequency band in the left channel audio signal and the right channel audio signal, and delays the phase of the first high frequency band by a predetermined phase delay amount. And further delaying the phase of the first high frequency band in the left-channel audio signal and the right-channel audio signal that have been amplified and phase-delayed by the predetermined phase delay amount. The audio signal processing method according to claim 4 or 5.

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