Audio player apparatus having sound analyzer and its control method

An audio player apparatus includes a first speaker disposed to output a sound from a front face of a flat panel television apparatus to the outside, a second speaker disposed to output a sound from a backside of the flat panel television apparatus to the outside, a microphone disposed on the backside of the flat panel television apparatus to receive the sound output from the second speaker and to convert the received sound into an electric signal, an analysis unit configured to detect a reflected sound and reflection time of the sound output from the second speaker based on a second audio signal supplied to the second speaker and the electric signal output from the microphone, and a phase correction unit configured to correct a phase of at least one of a first audio signal supplied to the first speaker and the second audio signal based on the reflection time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an audio player apparatus for controlling output characteristics of a plurality of speakers by analyzing acoustic characteristics of a reflected sound, and its control method.

2. Description of the Related Art

Conventionally, in a speaker apparatus, a woofer is disposed on sides and a tweeter is disposed at the front utilizing relative lack of directivity of a sound output from the bass-sound reproduction speaker. This arrangement can realize a speaker for a television apparatus, which can reproduce good bass sound and reduce a width of the apparatus (refer to Japanese Patent Application Laid-Open No. 06-105257).

Further, a conventional sound field measuring device picks up a signal to be measured that is reproduced in a measuring sound field, by a directional microphone having a plurality of directional axes, and analyzes the measured signal for each direction. This device enables evaluation of spread feelings or reverberation feelings regarding spatiality of the sound field, or location feelings of a sound image by analyzing reflected sound components in a room (refer to Japanese Patent Application Laid-Open No. 2007-225482).

However, in the case of the speaker apparatus of the television apparatus discussed in Japanese Patent Application Laid-Open No. 06-105257, a speaker unit is not disposed in a backside of the television apparatus. Therefore, the speaker apparatus cannot be an audio system which uses a reflected sound from a wall.

In the case of the sound field measuring device discussed in Japanese Patent Application Laid-Open No. 2007-225482, the inclusion of the plurality of directional axes in the microphone results in a complex configuration of the microphone. The microphone has to be disposed in a listening position to measure a sound field. A wiring line becomes accordingly longer, and a size of the entire device increases, creating a problem of complex handling. The microphone can be mounted on a device such as a remote controller set in a listening position. In this case, however, a microphone amplifier or an AD converter has to be disposed in the microphone, and a large amount of measured data has to be transmitted, causing a great increase in a circuit size of the remote controller. Furthermore, if the remote controller is set on a plane of a table, characteristics of the microphone are affected, so that it becomes difficult to accurately perform measurement.

SUMMARY OF THE INVENTION

The present invention is directed to an audio system which includes a speaker disposed in a backside and uses a reflected sound from a wall, and more particularly to an audio player apparatus which can analyze acoustic characteristics of a reflected sound with a compact configuration.

According to an aspect of the present invention, an audio player apparatus includes a first speaker disposed to output a sound from a front face of a flat panel television apparatus to the outside, a second speaker disposed to output a sound from a backside of the flat panel television apparatus to the outside, a microphone disposed to receive the sound output from the second speaker on the backside of the flat panel television apparatus and to convert the received sound into an electric signal, an analysis unit configured to detect a reflected sound and reflection time of the sound output from the second speaker based on a second audio signal supplied to the second speaker and the electric signal output from the microphone, and a phase correction unit configured to correct a phase of at least one of a first audio signal supplied to the first speaker and the second audio signal based on the reflection time.

When the flat television apparatus including the audio player apparatus of an exemplary embodiment of the present invention is installed before a wall, even if a distance from a wall surface or acoustic reflection characteristics of the wall surface change, good sound reproduction is performed with little interferences or characteristic fluctuations caused by an influence of a reflected sound.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a block diagram of an audio player apparatus according to a first exemplary embodiment of the present invention.

An input audio signal that has entered an input unit16is input to high-pass and low-pass filters12and13.

Under control of a control unit9, the high-pass and low-pass filters12and13respectively pass high-frequency and low-frequency components of the input audio signal to output them.

A phase correction unit11corrects a phase of an output of the high-pass filter12under control of the control unit9. The phase correction unit11may be configured to correct a phase of an output of the low-pass filer13, or correct phases of outputs of both filters.

A first volume adjustment unit7adjusts output amplitude of the phase correction unit11under control of the control unit9.

A second volume adjustment unit8adjusts output amplitude of the low-pass filter13under control of the control unit9.

A first amplification unit4amplifies an output of the first volume adjustment unit7to an output level that can drive a main speaker1(equivalent to first speaker).

A second amplification unit5amplifies an output of the second volume adjustment unit8to an output level that can drive a sub-speaker2(equivalent to second speaker).

A third amplification unit6amplifies an output of a microphone3to an output level that can be analyzed by an analysis unit10.

The main speaker1converts a high-frequency audio signal (equivalent to first audio signal), which is an output of the first amplification unit4, into an audible sound.

The sub-speaker2converts a low-frequency audio signal (equivalent to second audio signal), which is an output of the second amplification unit5, into an audible sound.

The microphone3receives a sound output from the sub-speaker2and its reflected sound into an electric signal.

The analysis unit10compares an output of the third amplification unit6with the output of the second amplification unit5to analyze a distance from a position of the sub-speaker2to an object which reflects the output sound of the sub-speaker2, and acoustic reflection characteristics.

The control unit9adjusts frequency characteristics, phase characteristics, and amplitude characteristics of the sounds output from the main speaker1and the sub-speaker2according to an analyzing result of the analysis unit10.

Referring to a flowchart ofFIG. 2, an operation of the audio player apparatus of the exemplary embodiment will be described below.

When the audio player apparatus is turned on to start processing, in step S1, the control unit9sets an output adjustment value of the second volume adjustment unit8to a specific value. As a result, the second amplification unit5amplifies a low-pass filtered signal among entered audio signals to input the amplified signal to the sub-speaker2. In response to the entered audio signal, the sub-speaker2outputs a low tone sound/signal.

The low tone sound output from the sub-speaker2is reflected around the speaker to become a reflected sound. In step S2, the analysis unit10compares a reflected sound converted into an electric signal by the microphone3, with a low-pass filtered signal output from the second amplification unit5to calculate/analyze reflection time.

In step S3, the control unit9sets/controls, based on the reflection time, characteristics of the phase correction unit11so as to prevent interferences caused by a phase difference between the output sound of the main speaker1directly reaching a listener and the output sound of the sub-speaker2reaching the listener as a reflected sound.

In step S4, the analysis unit10compares the output signal of the microphone3with the low-pass filtered signal output from the second amplification unit5to analyze a sound pressure level of the reflected sound and amplitude frequency characteristics.

In step S5, according to the sound pressure level and the amplitude frequency characteristics, the control unit9reduces a set volume of the second volume adjustment unit8to prevent generation of an excessive amount of bass sound if the sound pressure level of the reflected sound is high or there are much low-frequency components. In step S6, if the reflected sound contains much specific frequency components, the control unit9adjusts cutoff frequencies of the high-pass and low-pass filers12and13to prevent the frequency components from becoming excessive. This processing enables appropriate adjustment of output characteristics of the main speaker1and the sub-speaker2.

FIG. 3illustrates a configuration when the audio player apparatus of the exemplary embodiment is applied to a television apparatus. To efficiently convert the reflection of the sound output from the sub-speaker2into an electric signal, the microphone3is disposed near the sub-speaker2.

Referring to the flowchart ofFIG. 2again, an operation of the television apparatus will be described below. A flat panel television apparatus is installed with a wall on its backside. The main speaker1is disposed on a front side of the flat panel television apparatus, and the sub-speaker2is disposed on a backside.

In the signal output processing (step S1), the sound output from the sub-speaker2is reflected on the wall surface located on the backside of the television apparatus rear part and a reflected sound enters the microphone3. By using the reflected sound, in the reflection time analysis processing (step S2), a length of a path25that the reflected sound travels to reach a listener is calculated. The length of a path25varies according to a distance from the wall surface. The control unit9stores a path length difference table for calculating a difference in path length between a direct reaching path26and a reflection reaching path27based on the length of the path25that the reflected sound travels.

The control unit9adjusts, by using the path length table, phases of output sounds so as to prevent interferences between the output sound of the main speaker1which directly reaches the listener and the output sound of the sub-speaker2which is reflected on the wall to reach the listener. The interferences are caused by a phase difference that is generated by a path length difference (step S3).

More specifically, when sounds interfere with each other to cancel each other between the direct reaching path26and the reflection reaching path27as illustrated inFIG. 4A, the control unit9corrects a phase of the output sound of the first speaker1so as to set the phases to be equal to each other as illustrated inFIG. 4B.

Then, in reflection frequency characteristic analysis processing (step S4), the analysis unit10analyzes an acoustic reflectance ratio of the wall surface, reflection frequency characteristics, and a sound pressure level and frequency characteristics of a reflected sound. The sound pressure level and frequency characteristics change depending on a relationship between a distance from the sub-speaker2to the wall surface, and a spatial wavelength.

FIGS. 5A to 5Cillustrate examples of sound reproduction characteristics set by volume adjustment control processing (step S5) and filtering characteristic control processing (step S6) according to an analyzing result of the reflection frequency characteristic analysis processing (step S4).

As illustrated inFIG. 5A, when reflection level of a sound is virtually not dependent on a frequency, signal levels of the sub-speaker2and the main speaker1are set equal to each other, and a crossover level is set at an intermediate level.

As illustrated inFIG. 5B, when a reflected sound contains much low-frequency components, or when a sound pressure level is high, to prevent generation of an excessive amount of bass sound, the second volume adjustment unit8modulates an input signal by lowering a signal level of a low-frequency audio signal. As illustrated inFIG. 5C, when a reflected sound contains much specific frequency components, to prevent generation of an excessive amount of the specific frequency, the control unit9adjusts cutoff frequencies of the high-pass and low-pass filters12and13. As a result, a crossover level of frequency characteristics of high-frequency and low-frequency audio signals is modulated to a low level side.

The processing that has been described is concerned with only a right channel in a stereo configuration. For a left channel, similar processing is carried out by a second main speaker17, a second sub-speaker22, and a second microphone28independently of the right channel. Since the processing of the left and right channels is independently performed, the present invention can be easily applied even when the television apparatus is arranged nonparallel with the wall surface.

An angle with the wall surface is calculated based on a difference in length of microphone reaching paths25of the reflected sound, between the left and right channel, so that more accurate correction can be performed.

FIG. 7is a block diagram of an audio player apparatus according to a second exemplary embodiment of the present invention.

The audio player apparatus of the present exemplary embodiment includes a reference signal generation unit14configured to output a reference signal used for measurement, and a selection unit15. The selection unit15is configured to select, under control of a control unit9, one of outputs of a low-pass filter13and the reference signal generation unit14, and to output a low-frequency audio signal. Except for an operation relating to the selection unit15, operations according to the present exemplary embodiment are similar to the first exemplary embodiment.

When the apparatus is turned ON, the control unit9controls the selection unit15to select the output of the reference signal generation unit14. Then, by using a reference signal, correction processing of the flowchart ofFIG. 2is carried out as in the case of the first exemplary embodiment. After completion of the correction processing, the control unit9controls the selection unit15to switch to the output signal of the low-pass filter13based on the reference signal.

For the reference signal, a signal in which a signal level has fixed amplitude timewise and does not depend on frequency, or a signal having a signal level proportional to a frequency, can be used.

According to the exemplary embodiment, since the correction processing is carried out by using the reference signal that has the stable signal level, more accurate correction can be performed.

FIG. 8is a block diagram of an audio player apparatus according to a third exemplary embodiment of the present invention.

FIG. 9is a configuration diagram when the audio player apparatus of the third exemplary embodiment is applied to a television apparatus.

The audio player apparatus of the present exemplary embodiment has a 2.1 channel configuration in which a first input unit16and a second input unit21correspond to left and right channels of a stereo signal respectively. A sub-speaker2is a sub-woofer for reproducing low tone sounds of both channel inputs. A first main speaker1reproduces a high tone sound of a left channel input, and a second main speaker17reproduces a high tone sound of a right channel input. Audio signal through a high-pass filter20is adjusted in volume by a volume adjustment unit19, amplified by an amplification unit18and entered to the second main speaker17.

When a selection unit15selects a reference signal, as in the case of the second exemplary embodiment, signal output processing (step S1) and reflection time analysis processing (step S2) are carried out to recognize a length of a reflected sound microphone reaching path25. Then, a control unit9calculates a direct reaching path26and a reflection reaching path27. According to a result of this calculation, the control unit9performs phase control processing (step S3). Then, reflection frequency characteristic analysis processing (step S4), volume adjustment control processing (step S5), and filtering characteristics control processing (step S6) are carried out.

Audio signals received from the first and second input units16and21are converted into a monaural low-frequency signal by a low-pass filter13. In low-frequency signal output processing (step S7), left and right low tone sounds are output from the sub-speaker2. A sense of sound direction becomes duller as a frequency becomes lower. Thus, even in monaural reproduction, a sound can be reproduced with little influence on stereo separation in listening.

The sub-speaker2and the microphone3can be respectively configured only by one device, and by executing a series of the operations, stereo audio reproduction can be realized with few interferences or characteristic fluctuations caused by the influence of the reflected sound.

FIG. 10is a block diagram of an audio player apparatus according to a fourth embodiment of the present invention.

FIGS. 11A and 11Bare configuration diagrams when the audio player apparatus of the fourth embodiment is applied to a television apparatus.

The audio player apparatus of the present exemplary embodiment includes a second sub-speaker22disposed in a position different from that of a first sub-speaker2, and a second selection unit23configured to select one of the first and second sub-speakers2and22to supply an output of a second amplification unit5under control of a control unit9.

When a first selection unit15selects an output of a reference signal, as in the case of the second exemplary embodiment, the audio player apparatus is operated according to the flowchart ofFIG. 2. When it is detected that reflection time is within fixed time as a result of reflection time analysis processing (step S2), or that a reflection level is outside a fixed range as a result of reflection frequency characteristic analysis processing (step S4), the control unit9determines that the television apparatus is used in a wall-mounted state. Then, the second selection unit23selects the second sub-speaker22. Characteristics of a phase correction unit11, a sound volume of a second volume adjustment unit8, and cutoff frequencies of high-pass and low-pass filters12and13are switched to settings suited to characteristics of the second sub-speaker22.

In this case, since a sense of a sound direction becomes duller as a frequency becomes lower, even in monaural reproduction, a sound can be reproduced with little influences on stereo separation in listening.

In the above processing, an audio signal can be appropriately corrected by an output of the second sub-speaker22even when the television apparatus is used in the wall-mounted state. When the television apparatus is used with a certain space between a wall surface and the sub-speaker2, even if a distance or acoustic reflection characteristics of the wall surface changes, a sound can be reproduced with little interferences or characteristic fluctuations caused by an influence of a reflected sound.

FIG. 12is a block diagram of an audio player apparatus according to a fifth embodiment of the present invention.

FIG. 13is a configuration diagram when the audio player apparatus of the fifth embodiment is applied to a television apparatus.

As in the case of the fourth embodiment, a second sub-speaker22is disposed in a position different from that of a first sub-speaker2. The audio player apparatus of the exemplary embodiment includes, in place of the selection unit23, a balance adjustment unit24configured to adjust an output balance of a second amplification unit5.

As in the case of the fourth exemplary embodiment, correction processing is carried out according to the flowchart ofFIG. 2.

A control unit9determines that reproduction using reflection on a wall surface is difficult or there is no wall surface when reflection time is longer as a result of reflection time analysis processing (step S2), or a reflection level is lower as a result of reflection frequency characteristic analysis processing (step S4). In this case, a reproduction level of the second sub-speaker22is increased. Since a sense of a sound direction becomes duller as a frequency becomes lower, even in monaural reproduction, a sound can be reproduced with little influences on stereo separation in listening.

Further, characteristics of a phase correction unit11, a set volume of a second volume adjustment unit8, and cutoff frequencies of high-pass and low-pass filters12and13may be adjusted according to the reproduction level of the second sub-speaker22.

Thus, in the above processing, an audio signal can be corrected by an output of the second sub-speaker22even when the television apparatus is used in a state where reproduction using reflection on the wall surface by the sub-speaker2is difficult. When the television apparatus is used in a state where a wall surface having certain reflection characteristics is present behind the sub-speaker2, even if a distance or acoustic reflection characteristics of the wall surface change, sound reproduction can be performed with little interferences or characteristic fluctuations caused by an influence of a reflected sound.

This application claims priority from Japanese Patent Application No. 2008-023471 filed Feb. 4, 2008, which is hereby incorporated by reference herein in its entirety.