Signal processing device and signal processing method

A signal processing device includes: a resonant band-pass filter which extracts frequency components which cause resonance of a housing from an input signal; a harmonic generating unit which generates a harmonic signal for an output signal of the resonant band-pass filter; an adding unit which adds an output signal of the harmonic generating unit and at least a portion of frequency components of the input signal; and a resonant band-stop filter which removes the frequency components which cause the resonance of the housing from an output signal of the adding unit.

FIELD

The present disclosure relates to a signal processing device and a signal processing method.

BACKGROUND

With the recent advances in recording technology and broadcasting technology, the quality of broadcast content has improved. In particular, such advances have allowed an audio signal to include rich deep bass components. In contrast, in a television (TV) serving as a receiver of such an audio signal, resonance of the housing (so-called chattering) is likely to be caused by the deep bass components, as a result of design-oriented housing such as thinner or flat housing, and demands for cost reduction.

In order to solve such a problem, a technique has been developed for removing the frequency components which cause the chattering of the housing from an input audio signal (for example, Patent Literature (PTL) 1).

In the technique disclosed in PTL 1, when the frequency components which cause the chattering of the housing of a signal processing device are high, the level of attenuation performed by the band-stop filter is increased, whereas when the frequency components which cause the chattering of the housing are low, the level of attenuation performed by the band-stop filter is reduced. With this, the resonance of the housing caused by an input audio signal is reduced to prevent the sound of the input audio signal being impaired.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

However, in the technique disclosed in PTL 1, when the frequency components which cause the resonance of the housing rapidly varies in the input audio signal, detection of the frequency components which cause the resonance of the housing or correction or the like of the characteristics of the band-stop filter is lagged. This may cause the chattering or discomfort in sound due to rapidly performed correction of the characteristics of the band-stop filter.

The present disclosure has been conceived in view of such problems in the conventional techniques. An object of the present disclosure is to provide a signal processing device which is capable of reducing resonance of the housing caused by an input audio signal, as well as reducing impairment of the sound of the input audio signal.

Solution to Problem

In order to solve the above problems, a signal processing device according to one aspect of the present disclosure is a signal processing device which includes: a speaker; a housing to which the speaker is attached; a resonant band-pass filter which extracts a frequency component which causes resonance of the housing from an input signal; a harmonic generating unit which generates a harmonic signal for an output signal of the resonant band-pass filter; an adding unit which adds an output signal of the harmonic generating unit and at least a portion of a frequency component of the input signal; and a resonant band-stop filter which removes the frequency component which causes the resonance of the housing from an output signal of the adding unit.

Moreover, in order to solve the above problems, a signal processing method according to another aspect of the present disclosure is a signal processing method performed by a signal processing device which includes a speaker and a housing to which the speaker is attached. The method includes: extracting a frequency component which causes resonance of the housing from an input signal; generating a harmonic signal for the frequency component extracted in the extracting; adding the harmonic signal generated in the generating and at least a portion of a frequency component of the input signal; and removing the frequency component which causes the resonance of the housing from a signal obtained by the adding.

Advantageous Effects

According to the present disclosure, it is possible to provide a signal processing device which is capable of reducing resonance of the housing caused by an input audio signal, as well as reducing impairment of the sound of the input audio signal.

DESCRIPTION OF EMBODIMENT

First, the problems to be solved by the present disclosure and underlying knowledge forming basis of a signal processing device according to Embodiment 1 will be described with reference toFIG. 7andFIG. 8.FIG. 7is a block diagram illustrating a configuration of a signal processing device100aaccording to a conventional technique.FIG. 8is a block diagram illustrating a configuration of a signal processing device100bwhich uses missing fundamental phenomenon.

The signal processing device100aillustrated inFIG. 7includes: a band-pass filter140which extracts the frequency components which cause chattering of a housing101from an input signal; a variable band-stop filter143which attenuates the frequency components which cause the resonance of the housing101from the input signal; a detection unit141which detects the level of amplitude of an output signal of the band-pass filter140; and a control unit142which determines the gain (the level of attenuation) of the variable band-stop filter143according to a detection value of the detection unit141. Moreover, a speaker144which outputs the sound of an output signal of the variable band-stop filter143is attached to the housing101. In the conventional technique, with such a configuration, when the frequency components which cause the chattering of the housing101is high, the level of attenuation performed by the variable band-stop filter143is increased, and when the frequency components which cause the chattering of the housing101is low, the level of attenuation performed by the variable band-stop filter143is reduced. By doing so, the resonance of the housing101caused by the input audio signal is reduced, without impairing the sound of the input audio signal to the maximum extent.

Moreover, in the technique illustrated inFIG. 8, a psychoacoustic phenomenon referred to as the missing fundamental phenomenon is used. The missing fundamental phenomenon is a phenomenon in which even if the fundamental sound (for example, 50 Hz sound) is missing, when its harmonics (harmonic components) are present (when the fundamental sound is 50 Hz, and harmonics such as 100 Hz, 150 Hz, 200 Hz, 250 Hz, etc., are present), the missing fundamental sound is auditorily heard. Note that, in the present application, the second harmonic is referred to as the first overtone, the third harmonic is referred to as the second overtone, the (N+1) harmonic is referred to as the N-th overtone.

The signal processing device100billustrated inFIG. 8includes: a band-pass filter150which extracts the frequency components of the fundamental sound from an input signal; a harmonic generating unit151which generates a harmonic signal for an output signal of the band-pass filter150; an adding unit152which adds an output signal of the harmonic generating unit151and at least a portion of the frequency components of the input signal; and a speaker153which outputs the sound of an output signal of the adding unit152. With such a configuration, in the signal processing device100billustrated inFIG. 8, the low frequency components serving as the fundamental sound are added to the input signal, and outputted by the speaker153. Hence, even if the speaker153cannot reproduce the frequency components serving as the fundamental sound, a listener can hear the fundamental sound components. Therefore, the signal processing device100billustrated inFIG. 8is capable of maintaining the good sound quality even with an inexpensive speaker (see PTL 2). The signal processing device according to the present disclosure is configured with the afore-mentioned knowledge as the basis of the present disclosure.

Hereinafter, a signal processing device, which is capable of solving the above described problems, reducing resonance of the housing caused by an input audio signal, and reducing the sound of the input audio signal being impaired, will be described with the following embodiment as an example. The following embodiment shows one specific example. The numerical values, shapes, materials, structural elements, arrangement positions and connection states of the structural elements, steps, the order of the steps, etc., indicated in the embodiment below are examples, and are not intended to limit the present disclosure. Moreover, among the structural elements in the following embodiment, the structural elements which are not recited in the independent claims defining the most generic concept are described as optional structural elements.

A signal processing device1according to Embodiment 1 will be described with reference to the drawings.

FIG. 1illustrates a configuration of the signal processing device1according to Embodiment 1.FIG. 2is an external view of a digital television according to Embodiment 1.

The signal processing device1according to Embodiment 1 includes a speaker14, and a housing15to which the speaker14is attached. The signal processing device1is capable of reducing resonance of the housing15caused by an input audio signal, as well as reducing the sound of the input audio signal being impaired.

The signal processing device1illustrated inFIG. 1includes: a resonant band-pass filter10which extracts the frequency components which cause resonance of the housing15from an input signal; a harmonic generating unit11which generates a harmonic signal for an output signal of the resonant band-pass filter10; an adding unit12which adds an output signal of the harmonic generating unit11and at least a portion of the frequency components of the input signal; a resonant band-stop filter13which removes the frequency components which cause the resonance from an output signal of the adding unit12; and the speaker14which is attached to the housing15.

The signal processing device1illustrated inFIG. 1is, for example, disposed in the housing15of a digital television16whose external view is illustrated inFIG. 2.

InFIG. 2, the digital television16includes, for example, the speakers14, and a display17in the housing15. The speakers14illustrated inFIG. 2are the same as the speaker14illustrated inFIG. 1. Moreover, the housing15illustrated inFIG. 2is the same as the housing15illustrated inFIG. 1.

The operations of the signal processing device1thus configured will be described below.

First, the resonant band-pass filter10extracts the frequency components which cause resonance of the housing15from an input signal. For example, when the frequency components around 50 Hz are the cause of the resonance of the housing15, the resonant band-pass filter10extracts the frequency components including 50 Hz. Note that the resonant band-pass filter10may be a low-pass filter including 50 Hz.

Subsequently, the harmonic generating unit11generates a harmonic signal for an output signal of the resonant band-pass filter10. A harmonic signal may be generated by any type of unit, and, for example, may be generated by the unit disclosed in PTL 2.

Subsequently, the adding unit12adds an output signal of the harmonic generating unit11and the input signal. Here, the input signal that is added to the output signal of the harmonic generating unit11may include at least a portion of the frequency components of the input signal. For example, the input signal may include the frequency components processed for sound quality adjustment.

Subsequently, the resonant band-stop filter13removes the frequency components which cause the resonance from an output signal of the adding unit12. In the signal processing device1according to Embodiment 1, the frequency components around 50 Hz are assumed to be the cause of the resonance of the housing15, and thus, the resonant band-stop filter13attenuates the frequency band including 50 Hz. Note that the sound can be maintained because the harmonic components have been generated by the harmonic generating unit11. Hence, the resonant band-stop filter13may attenuate the frequency components of the band including 50 Hz. This reliably reduces the chattering of the housing15.

Finally, the speaker14outputs the sound of an output signal of the resonant band-stop filter13. The speaker14is attached to the housing15. The frequency components which cause the resonance of the housing15have been removed from the output signal of the resonant band-stop filter13.

As described above, the signal processing device1according to Embodiment 1 includes: the resonant band-pass filter10which extracts the frequency components which cause the resonance of the housing15from an input signal; the harmonic generating unit11which generates a harmonic signal for an output signal of the resonant band-pass filter10; the adding unit12which adds an output signal of the harmonic generating unit11and at least portion of the frequency components of the input signal; and the resonant band-stop filter13which removes the frequency components which cause the resonance from an output signal of the adding unit12. With this, it is possible to reduce the resonance of the housing15. Moreover, the frequency components which have been attenuated to reduce the resonance of the housing15can be auditorily compensated by the psychoacoustic phenomenon of the missing fundamental.

Note that, in the signal processing device1according to Embodiment 1, the frequency components which cause the resonance of the housing15is assumed to be 50 Hz, but the value differs depending on the devices. For example, when the frequency components which cause the resonance of the housing15is 100 Hz, the third harmonic (second overtone) is already 300 Hz, and thus, generating much higher harmonics results in an output of rather an unpleasant noise. In contrast, when the frequency components which cause the resonance of the housing15is 50 Hz, even if the fifth harmonic is generated, the fifth harmonic is still 250 Hz which is less likely to be an unpleasant noise. Accordingly, the level of harmonic that is generated differs depending on the level of the frequency components which cause the resonance of the housing15.

Hereinafter, a configuration of a signal processing device2for adjusting the level of harmonic that is generated depending on the level of the frequency components which cause the resonance of the housing15will be described.FIG. 3is a block diagram illustrating a configuration of the signal processing device2for meeting various resonant frequencies.

As illustrated inFIG. 3, the signal processing device2includes the resonant band-pass filter10, a harmonic generating unit21, an adding unit22, a resonant band-stop filter23, a speaker24, a setting unit25, and a harmonic adjusting unit26.

The signal processing device2is different from the signal processing device1illustrated inFIG. 1in that the signal processing device2includes the setting unit25which sets information on the characteristics of the housing15, and the harmonic adjusting unit26which adjusts an output signal of the harmonic generating unit21according to the information set by the setting unit25. The setting unit25sets, as the information on the characteristics of the housing15, information (frequency F) that indicates the frequency components which cause resonance of the housing15.

With such a configuration, when the setting unit25sets the frequency F which causes the resonance of the housing15, the harmonic adjusting unit26performs adjustment such that a signal including an N-th overtone generated by the harmonic generating unit21is sent to the adding unit22, when the frequency F is lower than a predetermined value (P). Moreover, when the frequency F is higher than or equal to the predetermined value (P), the harmonic adjusting unit26performs adjustment such that a signal including an M-th overtone (where M is less than N) generated by the harmonic generating unit21is sent to the adding unit22.

Here, the relationships among F, P, and N described above are determined as described below. Harmonic components tend to be an unpleasant sound when reaching overly high frequency components. For example, it is assumed that when harmonic components are present in the frequency bands above 400 Hz, the harmonic components become an unpleasant sound. Moreover, presence of overly higher harmonic components also results in an unpleasant sound. For example, presence of components up to the third overtone (fourth harmonic) is enough to make the fundamental sound sufficiently perceived due to the missing fundamental phenomenon, and thus, the higher harmonic components are unnecessary. In this case, N is 3, and P is 100. In other words, when the frequency F is higher than or equal to 100 Hz, the third overtone is higher than or equal to 400 Hz, which results in an unpleasant sound being perceived. On the other hand, when the frequency F is lower than 100 Hz, the third overtone is less than 400 Hz, and thus, generating up to the third overtone does not result in an unpleasant sound. Accordingly, when the frequency F is lower than P, the N-th overtone is generated, and when the frequency F is higher than or equal to P, the M-th overtone, which is lower than the N-th overtone, is generated. Note that the above described values of F, P, N, and M are examples.

By doing so, control can be performed such that the harmonic components do not have adverse effects on the resultant sound. Note that the above described degree (M-th) may be 0.

Moreover, the sensitivity which causes resonance of the housing15(resonance sensitivity) also differs depending on the devices. Here, the term “sensitivity” refers to how sensitive the resonance occurs. When the value of the sensitivity is greater than a predetermined value, the sensitivity is assumed to be high (the state where chattering of the housing15easily occurs), and when the value is less than or equal to the predetermined value, the sensitivity is assumed to be low.

A configuration of a signal processing device3for adjusting the sensitivity of resonance of the housing15will be described below.FIG. 4is a block diagram illustrating a configuration of the signal processing device3for meeting various resonance sensitivities.

As illustrated inFIG. 4, the signal processing device3includes the resonant band-pass filter10, a harmonic generating unit31, an adding unit32, a resonant band-stop filter33, a speaker34, a setting unit35, a harmonic adjusting unit36, and a filter adjusting unit37.

The signal processing device3is different from the signal processing device1illustrated inFIG. 1in that the signal processing device3includes: the setting unit35which sets information on the characteristics of the housing15; the harmonic adjusting unit36which adjusts an output signal of the harmonic generating unit31according to the information set by the setting unit35; and a filter adjusting unit37which adjusts the gain (level of attenuation) of the resonant band-stop filter33according to the information set by the setting unit35. The setting unit35sets information indicating the resonance sensitivity of the housing15as the information on the characteristics of the housing15.

With such a configuration, the harmonic adjusting unit36amplifies an output signal of the harmonic generating unit31by A times and sends the amplified signal to the adding unit32, when the information (S) indicating the sensitivity set by the setting unit35is greater than a predetermined value (for example, the reciprocal of X below) (when chattering of the housing15easily occurs). Moreover, when the information (S) indicating the sensitivity set by the setting unit35is less than or equal to the predetermined value, the harmonic adjusting unit36amplifies the output signal of the harmonic generating unit31by B times (where B is less than A), and sends the amplified signal to the adding unit32. Note that A and B are values which satisfy the relation of A>B. Here, A and B each may be set to be greater than 1.

Moreover, when the information (S) indicating the sensitivity set by the setting unit35is greater than the predetermined value (when chattering of the housing15easily occurs), the harmonic adjusting unit36sets the gain of the resonant band-stop filter33to be −G (so that the level of attenuation is high). Moreover, when the information (S) indicating the sensitivity set by the setting unit35is less than or equal to the predetermined value, the harmonic adjusting unit36sets the gain of the resonance band-stop filter33to be −H which is greater than −G (so that the level of attenuation is low). By doing so, even when the chattering of the housing15easily occurs, the chattering can be reliably reduced. The frequency band loss caused by the chattering can be compensated by increasing the harmonics. Moreover, when the chattering of the housing15is less likely to occur, sound close to the original sound can be output by reducing the harmonics.

Here, the above described S is as described below. When a signal having an amplitude which gradually increases is output and the amplitude value at which the chattering of the housing15starts to occur is X, the chattering of the housing15is less likely to occur when X is large, and the chattering of the housing15is likely to occur when X is small. Since it is defined that the chattering is likely to occur the greater the value of S becomes, S is an index which decreases in accordance with an increase in X, such as S being the reciprocal of X. Moreover, the above described −G and −H are values obtained by decibel conversion of the gain of the filter. For example, −G is −18 dB, and −H is −6 dB. Note that the above values of H and G are examples.

The configurations of the respective units, filters and the like of the signal processing devices1to3may be entirely or partially implemented by hardware, or software.

FIG. 5is a block diagram of a digital television16according to Embodiment 1, and illustrates a configuration of the digital television16implementing the signal processing devices1to3by software.

InFIG. 5, the digital television16includes the speaker14, the display17, a system LSI (Large Scale Integration: large scale integrated circuit)71, an antenna72, and a keyboard73. The system LSI71includes a tuner711, an AV decoder712, a memory713, a central processing unit (CPU)714, an interface (I/F)715, audio output unit716, and a video output unit717.

The digital television16may include, among the above structural elements, only the speaker14, the display17, and the system LSI71. In that case, the digital television16may be connected to the antenna72or the keyboard73by a cable or the like.

The antenna72receives a broadcast signal of the digital television16, and transmits the received signal to the System LSI71. The system LSI71outputs an audio signal and a video signal by demodulating the broadcast signal transmitted from the antenna72. The speaker14converts the audio signal transmitted from the system LSI71into sound and outputs the sound. The display17converts the video signal transmitted from the system LSI71into video and outputs the video.

In the system LSI71, the broadcast signal is converted to a digital signal of a desired channel by the tuner711, and transmitted to the AV decoder712. In the AV decoder712, the digital signal transmitted from the tuner711is decoded to generate an audio signal and a video signal. The memory713stores a program for realizing the functions of the above-described signal processing devices when executed by the CPU714. When the CPU714reads out the program from the memory713and executes the program, the audio signal generated by the AV decoder712is processed and transmitted to the audio output unit716. The audio output unit716outputs the audio signal. The video signal generated by the AV decoder712is transmitted to the video output unit717. The video output unit717outputs the video signal.

The system LSI71further includes an interface715. An external input unit, such as the keyboard73, can be connected to the interface715. The interface715is used to set the frequency components which cause resonance of the housing15of the digital television16, information indicating the resonance sensitivity of the housing15, and the like to the system LSI71using the keyboard73or the like.

Next, a signal processing method performed by the signal processing device1will be described.FIG. 6is a flowchart of the operations of the signal processing device1according to Embodiment 1.

As illustrated inFIG. 6, first, the signal processing device1according to Embodiment 1 receives an audio signal (step S81). Subsequently, the resonant band-pass filter10extracts the resonant frequency components of the housing15included in the audio signal received at step S81(step S82). Subsequently, a harmonic signal is generated, by the harmonic generating unit11, for the resonant frequency components of the housing15extracted in step S82(step S83). Next, the adding unit12adds the harmonic signal generated in step S83and the audio signal received by the signal processing device1in step S81(step S84). Then, the resonant band-stop filter13removes the frequency components which cause the resonance from the signal obtained by the adding in step S84(step S85). With the signal processing method as described above, the signal processing device1is capable of reducing the resonance of the housing15, as well as auditorily compensating the frequency components attenuated in order to reduce the resonance of the housing15, using the psychoacoustic phenomenon of the missing fundamental.

Note that the operations similar to those performed by the signal processing device1are performed by the signal processing device2and the signal processing device3, and thus, the descriptions thereof will be omitted.

As described above, according to the signal processing devices1to3according to Embodiment 1, it is possible to reduce the resonance of the housing caused by an input audio signal, and to reduce the sound of the input audio signal being impaired.

Although the signal processing device according to one or more aspects has been described based on the embodiment, the present disclosure is not limited to such an embodiment. Although only one exemplary embodiment of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure.

INDUSTRIAL APPLICABILITY

The signal processing device according to the present disclosure can be applied to televisions, car audio, portable devices such as smart phones and tablets.