JP5983835B2 - Audio signal processing device - Google Patents

Description

  The present invention relates to an audio signal processing apparatus that performs various processes on an input audio signal.

  2. Description of the Related Art Conventionally, for example, a process as shown in Patent Document 1 is known as a method of giving a sense of sound spread with a monaural speaker.

  In Patent Document 1, an L-R signal that is a difference component between an L-channel input signal and an R-channel input signal is generated and added to the L + R signal with a predetermined gain through a low-pass filter, so that a sense of sound spread is obtained. What gives is described.

Japanese Patent No. 4526757

  An object of the present invention is to provide an audio signal processing apparatus that adjusts the level of a main signal obtained by synthesizing a surround signal including a surround component and audio signals of a plurality of channels.

  An audio signal processing apparatus according to the present invention includes an input unit that inputs audio signals of a plurality of channels, a surround signal generation unit that generates a surround signal including a surround component from the audio signals of the plurality of channels, and the audio signals of the plurality of channels. A main signal generator for generating a synthesized main signal, a first level adjuster for adjusting the gain of the main signal, a second level adjuster for adjusting the gain of the surround signal, the first level adjuster, and And an output unit that synthesizes and outputs the output signal of the second level adjuster.

  The audio signal processing device includes a frequency processing unit that changes a frequency characteristic of a gain of the surround signal, and a phase shift processing unit that changes a frequency characteristic of the phase of the main signal, and the first level adjuster Adjusts the gain of the output signal of the phase shift processing unit, the second level adjuster adjusts the gain of the output signal of the frequency processing unit, and the frequency processing unit changes the frequency characteristics of the gain. And a phase frequency characteristic corresponding to the phase frequency characteristic of the phase shift processing unit.

  In the method of Patent Document 1, since a low-pass filter is used, the phase of the LR signal does not change, but the phase of the high frequency side changes. For this reason, when the LR signal is added to the L + R signal, the frequency characteristics are lost, and only the low frequency is emphasized as the gain of the LR signal is increased. However, the audio signal processing apparatus of the present invention changes the frequency characteristics and phase of a surround signal (for example, an LR signal) including a surround component, but synthesizes audio signals of a plurality of channels according to the phase change of the surround signal. By changing the phase of the main signal (for example, L + R signal), the phase difference between the surround signal and the main signal is controlled. If this phase difference is maintained in a certain band (for example, less than 10 kHz, which has a great influence on sound quality), the frequency characteristic does not collapse within the band, and only a certain band is emphasized even if the gain of the surround signal is increased. Disappears. Further, when the gain of the second level adjuster is increased, the surround feeling is enhanced, and when the gain of the first level adjuster is increased, the in-phase component is enhanced. For example, if the source includes human voice, the gain of the first level adjuster may be increased to emphasize the human voice. Conversely, if the source is BGM, The gain of the second level adjuster may be lowered to emphasize the surround feeling.

  Further, the phase difference between the main signal and the surround signal may be maintained only in a specific band, but it is preferable in terms of sound quality to be maintained in the entire audible band.

  Further, changing the frequency characteristic and phase of the surround signal can be realized by using a first-order bandpass filter. In this case, the center frequency of the bandpass filter is desirably set to a frequency (generally about 300 Hz to 5 kHz) that affects the sense of localization.

  The phase shift processing unit can be realized by a first-order all-pass filter. The all-pass filter has a characteristic in which the phase gently changes from 0 degrees to -180 degrees from the low frequency band to the high frequency band. Therefore, the band-pass filter has a characteristic that matches the frequency characteristic (phase characteristic) of the phase of the all-pass filter. It is preferable to set the phase characteristic. For example, the frequency at which the 90-degree phase shift occurs matches the center frequency of the bandpass filter. In addition, the frequency characteristic (gain frequency characteristic) of the bandpass filter is set so that the phase characteristic of the bandpass filter is substantially the same as the phase characteristic of the allpass filter.

  The phase shift processing unit and the frequency processing unit can be realized by digital signal processing using a DSP, but can also be realized by using an analog circuit such as an operational amplifier, a resistor, and a capacitor. is there. In the case of an analog circuit, it can be realized at a very low cost compared to digital signal processing using a DSP.

  The present invention emphasizes the surround feeling of the synthesized monaural signal by adjusting the level when synthesizing the surround signal including the surround component and the main signal obtained by synthesizing the audio signals of a plurality of channels. The voice of a person can be emphasized.

It is a block diagram which shows the structure of a signal processing apparatus. FIG. 2A is a diagram illustrating the frequency characteristics of the amplitude, and FIG. 2B is a diagram illustrating the frequency characteristics of the phase. It is a block diagram which shows the structure of the signal processing apparatus which concerns on the modification 1. It is a block diagram which shows the structure of the signal processing apparatus which concerns on the modification 2. It is a block diagram which shows the structure of the signal processing apparatus which concerns on the modification 3.

  FIG. 1 is a block diagram showing the configuration of the signal processing apparatus of the present invention. The signal processing apparatus according to the present embodiment is an apparatus that inputs audio signals of a plurality of channels, mixes them down, and outputs them as monaural audio signals. In the present embodiment, all audio signals will be described as analog signals unless otherwise specified.

  The signal processing device includes an input interface (I / F) 11, an adder 12, an adder 13, an all-pass filter (APF) 14, a band-pass filter (BPF) 15, a level adjuster 16, a level adjuster 17, and an output I. / F18 is provided.

  The input I / F 11 corresponds to the input unit of the present invention, and inputs an audio signal from another device or a content reproduction unit (not shown) in the own device. In this embodiment, an example in which an analog audio signal is input will be described. When a digital audio signal is input, a D / A converter is provided in the input I / F 11. In addition, when inputting encoded data such as MP3, a decoder is also provided. Among the input audio signals, the left channel (L) signal and the right channel (R) signal are supplied to the adder 12 and the adder 13, respectively.

  The adder 12 corresponds to the main signal generation unit of the present invention, adds the L signal and the R signal, generates a sum signal (L + R signal), and outputs it. The adder 13 corresponds to the surround signal generation unit of the present invention, and generates and outputs a difference signal (LR signal) by subtracting the R signal from the L signal. The difference signal may be generated as an RL signal obtained by subtracting the L signal from the R signal.

  Such a difference signal is obtained by eliminating the in-phase component of the L signal and the R signal, and includes a component that mainly affects a surround feeling such as reverberation. The signal processing apparatus according to the present embodiment adds the difference signal to the sum signal, thereby giving a broad sense of surround even when the sum signal is output from a single speaker and monaural reproduction is performed. It can be done. However, when the sum signal and the difference signal are simply added, the L signal component or the R signal component is deleted. Therefore, the signal processing apparatus of the present invention performs phase shift processing and frequency processing with the APF 14 and the BPF 15 as shown below, so that the L signal component and the R signal component are eliminated even if the sum signal and the difference signal are added. Signal processing that is not performed and the frequency characteristic of the output signal at the final stage does not change significantly is realized.

  The APF 14 corresponds to the phase shift processing unit of the present invention, and is a first-order filter that changes the phase by 90 degrees while maintaining the frequency characteristic (gain frequency characteristic) of the input signal. An L + R signal is input to the APF 14. The BPF 15 corresponds to the frequency processing unit of the present invention, and is a primary filter that passes a predetermined frequency band of an input signal. The LPF signal is input to the BPF 15.

  The frequency at which the 90 degree phase shift of the APF 14 and the center frequency of the BPF 15 are set to be the same frequency. In the present embodiment, the circuit characteristics are set so that a 90-degree phase shift occurs at 1 kHz for the APF 14 and the center frequency of the BPF 15 is 1 kHz. Note that the frequency at which 90-degree phase shift in the APF 14 and the center frequency of the BPF 15 are set to a frequency band (approximately 300 Hz to 5 kHz) that affects localization, but actually the characteristics of the speaker and the input audio signal (source) Set as appropriate according to the contents of. The frequency characteristic (gain frequency characteristic) of the BPF 15 is set according to the frequency characteristic (phase characteristic) of the phase of the APF 14 as will be described in detail later.

  The output signal of the APF 14 is input to the level adjuster 16, and the output signal of the BPF 15 is input to the level adjuster 17. The level adjuster 16 and the level adjuster 17 adjust the levels of the input L + R signal and LR signal, respectively, and output them to the output I / F 18.

  If the gain of the level adjuster 17 is increased, the surround feeling is enhanced, and if the gain of the level adjuster 16 is increased, the in-phase component is enhanced. For example, if the source includes human voice, the gain of the level adjuster 16 may be increased to emphasize the human voice. Conversely, if the source is BGM, The gain of the adjuster 16 may be lowered to emphasize the surround feeling. Or you may set according to a listener's liking. Moreover, although the gain of the level adjuster 16 and the level adjuster 17 may be fixed, it is good also as an aspect which can provide a user interface and can adjust each gain.

  The output I / F 18 corresponds to an output unit of the present invention, synthesizes the L + R signal output from the level adjuster 16 and the LR signal output from the level adjuster 17, and outputs the combined signal to the outside. Output to. Although not shown, the output signal is amplified by the power amplifier and then output to the speaker.

  Next, the frequency characteristics and phase characteristics of the APF 14 and the BPF 15 will be described with reference to FIG. FIG. 2A is a diagram illustrating frequency characteristics (gain frequency characteristics) of the APF 14, the BPF 15, and the output signal (the output signal of the output I / F 18). FIG. 2B illustrates the APF 14, the BPF 15, and the output. It is a figure which shows the phase characteristic (frequency characteristic of a phase) of a signal.

  As shown in FIGS. 2 (A) and 2 (B), the frequency characteristic of the APF 14 is completely flat (0 dB in the entire band), and gently from 0 degrees to -180 degrees from the low frequency band to the high frequency band. Have a phase characteristic in which the phase changes. In the present embodiment, the circuit characteristics of the APF 14 are set so that the phase is −90 degrees at 1 kHz, which has a great effect on the sense of localization.

  Further, as shown in FIG. 2A, the center frequency of the BPF 15 is set to 1 kHz. As shown in FIG. 2B, the phase does not change at this center frequency. Therefore, at 1 kHz, the phase difference between the output signal of the APF 14 and the output signal of the BPF 15 is 90 degrees. In this example, the peak gain of the BPF 15 is −3 dB. However, as an example, the gain characteristic of the BPF 15 (the gain of the level adjuster 17) is set so that the gain of the output signal is −6 dB. Therefore, the actual peak gain of the BPF 15 is appropriately set according to the required gain of the output signal.

  As shown in FIG. 2B, the circuit characteristics of the BPF 15 are set so as to exhibit substantially the same phase characteristics as the phase characteristics of the APF 14. That is, the frequency characteristic of the BPF 15 is gently set to set a wide band (for example, a -3 dB width of about 300 Hz to 5 kHz), and the circuit characteristic corresponding to the phase characteristic of the APF 14 is set.

  Thus, since the APF 14 and the BPF 15 maintain the phase difference over the entire audible band, the output signal of the APF 14 and the output signal of the BPF 15 are added as shown in the frequency characteristics of the output signal in FIG. Even if the gain of the difference signal is increased (for example, to the same gain as the sum signal), the frequency characteristics will not be greatly degraded, and only a certain band will not be over-emphasized, giving a broad sense of surround without affecting the sound quality. It becomes possible.

  Further, the APF 14 and the BPF 15 having the above characteristics can be realized at a very low cost by using an analog circuit such as an operational amplifier, a resistor, and a capacitor. However, the phase shift processing unit and the frequency processing unit of the present invention can also be realized by digital signal processing using a DSP, respectively, depending on the signal processing unit that changes only the phase of the sum signal and the phase change of the sum signal. And a signal processing unit for changing the frequency characteristics and phase of the difference signal.

  In the above embodiment, the example has been shown in which the frequency characteristic of the BPF 15 is set so that the phase difference with the APF 14 is maintained over the entire audible band. However, in the present invention, the phase difference needs to be maintained over the entire audible band. Absent. In particular, the phase difference may only be maintained in a band (for example, less than 10 kHz) that greatly affects sound quality.

  In this embodiment, an example in which the L channel and the R channel are reproduced using a monaural speaker is shown. However, even when the input signal is the rear L channel (SL) and the rear R channel (SR), The present invention can be applied. In this case, the sum signal becomes the SL + SR signal and the APF 14 performs phase shift processing, and the difference signal becomes the SL-SR signal and the BPF 15 performs phase shift processing and frequency processing. In this case, it is suitable when outputting the audio signal of SL channel and SR channel from one speaker installed in the back of a listener.

  Further, the signal processing apparatus of the present invention can be applied to a case where a multi-channel audio signal is further input.

(Modification 1)
FIG. 3 is a block diagram illustrating a configuration of the signal processing device according to the first modification. Components that are the same as those in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted. The signal processing apparatus shown in FIG. 3 includes a level adjuster 21 that adjusts the level of the LFE signal in order to perform 2.1 channel reproduction including a dedicated low frequency (LFE) channel. The LFE signal whose level has been adjusted by the level adjuster 21 is input to the output I / F 18.

  The output I / F 18 combines the L + R signal output from the level adjuster 16, the LR signal output from the level adjuster 17, and the LFE signal output from the level adjuster 21. The later signal is output to the outside. In this way, even if the input signal is 2.1 channel, it can be output as a monaural signal and a wide surround sound can be realized even when it is output from a single speaker.

(Modification 2)
FIG. 4 is a block diagram illustrating a configuration of a signal processing device according to the second modification. In addition, about the structure which is common in FIG. 3, the same code | symbol is attached | subjected and the description is abbreviate | omitted. The signal processing apparatus of FIG. 4 performs level adjustment for adjusting the level of the C signal in order to perform 5.1 channel reproduction including the center channel (C), rear L (SL) channel, and rear R (SR) channel. 22, a level adjuster 23 for adjusting the level of the SL signal, and a level adjuster 24 for adjusting the level of the SR signal. The C signal level-adjusted by the level adjuster 22, the SL signal level-adjusted by the level adjuster 23, and the SR signal level-adjusted by the level adjuster 24 are input to the output I / F 18, respectively.

  The output I / F 18 outputs an L + R signal output from the level adjuster 16, an LR signal output from the level adjuster 17, an LFE signal output from the level adjuster 21, and an output from the level adjuster 22. The combined C signal, the SL signal output from the level adjuster 23, and the SR signal output from the level adjuster 24 are combined, and the combined signal is output to the outside. In this way, even if a 5.1 channel input signal is output as a monaural signal and output from a single speaker, a wide surround sound can be realized.

(Modification 3)
Further, FIG. 5 is a block diagram illustrating a configuration of a signal processing device according to the third modification. In addition, about the structure which is common in FIG. 4, the same code | symbol is attached | subjected and the description is abbreviate | omitted. The signal processing device in FIG. 5 adds an SL signal and an SR signal to generate a sum signal (SL + SR signal), and subtracts the SR signal from the SL signal to obtain a difference signal (SL-SR signal). And an adder 32 for generation. 5 includes an APF 33 that inputs an SL + SR signal, a BPF 34 that inputs an SL-SR signal, a level adjuster 35 that adjusts the level of the output signal of the APF 33, and a level adjustment of the output signal of the BPF 34. And a level adjuster 36 for performing the above.

  The APF 33 and the BPF 34 are filters having characteristics similar to those of the APF 14 and the BPF 15, respectively. That is, the SL + SR signal is phase shifted 90 degrees at 1 kHz by the APF 33, and the SL-SR signal is in a state where the phase difference from the SL + SR signal is maintained at 90 degrees in the entire audible band by the BPF 15.

  The SL + SR signal is level-adjusted by the level adjuster 35, and the SL-SR signal is level-adjusted in the level adjustment period 36 and then input to the output I / F 18, respectively.

  The output I / F 18 outputs an L + R signal output from the level adjuster 16, an LR signal output from the level adjuster 17, an LFE signal output from the level adjuster 21, and an output from the level adjuster 22. The combined C signal, the SL + SR signal output from the level adjuster 35, and the SL-SR signal output from the level adjuster 36 are combined, and the combined signal is output to the outside. Even in this case, the phase difference between the SL + SR signal and the SL-SR signal is maintained at 90 degrees in the entire audible band, and the frequency characteristics are not greatly deteriorated, and it is possible to further enhance the surround sound feeling that does not affect the sound quality. become.

11 ... Input I / F
12 ... Adder 13 ... Adder 14 ... APF
15 ... BPF
16 ... Level adjuster 17 ... Level adjuster 18 ... Output I / F

Claims (6)

An input unit for inputting multi-channel audio signals;
A surround signal generation unit that generates a surround signal including a surround component from the audio signals of the plurality of channels;
A frequency processing unit that changes a frequency characteristic of the gain of the surround signal;
A main signal generation unit that generates a main signal obtained by synthesizing the audio signals of the plurality of channels;
A phase shift processing unit for changing a frequency characteristic of a phase of the main signal;
A first level adjuster for adjusting the gain of the output signal of the phase shift processing unit ;
A second level adjuster for adjusting the gain of the output signal of the frequency processing unit ;
An output unit that synthesizes the output signals of the first level adjuster and the second level adjuster and outputs the result as a monaural signal;
Equipped with a,
The frequency processing unit changes a frequency characteristic of a gain and has a frequency characteristic of a phase corresponding to the phase frequency characteristic of the phase shift processing unit. The audio signal processing apparatus according to claim 1 , wherein a phase difference between the main signal and the surround signal is held over the entire audible band. The frequency processing unit, the audio signal processing apparatus according to claim 1 or claim 2, characterized in that a band-pass filter. The audio signal processing apparatus according to claim 3 , wherein the center frequency of the band-pass filter is a frequency that affects a sense of localization. The phase shift processing unit is an all-pass filter,
The band-pass filter, the audio signal processing apparatus according to claim 3 or claim 4 phase difference between the all-pass filter is characterized by having the property of being retained in the entire audio band. The phase processing unit and the frequency processing unit, the audio signal processing apparatus according to any one of claims 1 to 5, characterized in that it is implemented by an analog circuit.

Images