JP5535428B2 - Audio signal output method, speaker system, portable device, and computer program - Google Patents

Description

  The present invention relates to output of an audio signal in a speaker system. In particular, the present invention relates to a speaker system that sounds a small and thin speaker such as a speaker system of a portable device.

  Various portable devices such as a cellular phone, a notebook computer, and a personal digital assistant (PDA) are provided with a speaker that outputs sound. Such portable devices are always required to be smaller and thinner. For example, a cellular phone is provided with a speaker for ringing a ringtone and a ringing melody, and is required to be small and thin in order to improve portability. For this reason, small and thin speakers are often employed in portable devices.

  Compared with large-diameter / thick speakers, small and thin speakers tend to have a lower maximum output volume, and a lower mid-range output sound pressure. For example, piezoelectric ceramic speakers, which are being developed as thin speakers, have poor low-frequency characteristics when compared to the characteristics of large-diameter electromagnetic speakers. Overall, the sound pressure is low, and it is difficult to ensure sound quality and volume.

  In order to improve the low-middle characteristics of such a small and thin speaker, there is a conventional technique for amplifying the electric signal level of the entire band and inputting it to the speaker amplifier. However, if this is done, an input corresponding to the output exceeding the power supply voltage is made to the speaker amplifier, and a phenomenon of outputting a distorted sound limited to the power supply voltage, so-called clipping is likely to occur, and as a result, there is no distortion. There is a problem that it is difficult to achieve both sound and high sound pressure.

  Patent Document 1 describes a technique for adjusting the frequency characteristics of an audio signal according to the open / close state of a foldable mobile phone as a conventional technique for improving the sound pressure and sound quality of a small and thin speaker.

JP 2004-328343 (paragraphs 0041-0047)

  The present invention has been made in view of such a situation, and a problem to be solved by the present invention is to provide a speaker system capable of outputting with a large sound pressure without being accompanied by sound quality degradation due to clips. .

  In order to solve the above-described problems, the present invention provides the following techniques. That is, according to the present invention, in the audio signal output method, the digital signal processing device attenuates the level of the first band with respect to the audio signal, and the first band is defined according to the amount of attenuation. An audio signal comprising: a step 1 for performing signal processing for amplifying different second band levels; and a step 2 for outputting the attenuated and amplified audio signal from a speaker through a speaker amplifier. Provide an output method.

  The first band may be higher or lower than the second band, and may include both high and low bands.

  Even when the first band includes a band higher than the second band, or when the first band includes a band lower than the second band, the signal is clipped by the speaker amplifier. The dynamic range up to can be expanded. For example, attenuating the low range where it is difficult to obtain sufficient sound pressure due to the characteristics of the speaker, while amplifying the mid range, does not make a significant difference in audibility, and the dynamic range until the signal is clipped by the speaker amplifier Can be expanded.

  In particular, when a band higher than the second band is included as the first band, for example, when the middle band is amplified while the high band is attenuated, the power consumption of the speaker system is added to the above effect. The effect of reducing is obtained. This effect is remarkable when the speaker is a piezoelectric ceramic speaker.

  The first band is preferably determined according to the characteristics of the speaker. The present invention has the effect of increasing the volume feeling without substantially impairing the sound quality, but this effect can be maximized by determining the band to be attenuated according to the characteristics of the speaker.

  More specifically, in step 1, obtaining a sample of an audio signal, obtaining an average spectrum of the sample, and reducing the first band of the sample to a predetermined level according to the output characteristics of the speaker. It is conceivable to include a step, determining the power of the sample with a reduced level of the first band, and amplifying the second band of samples according to the power.

  The present invention also provides an equalizer that attenuates the level of the first band with respect to the audio signal and amplifies the level of the second band different from the first band according to the amount of attenuation in the speaker system. And a speaker amplifier that amplifies the output of the equalizer and a speaker driven by the speaker amplifier.

  In particular, it is effective when applied to a speaker system including a piezoelectric ceramic speaker.

  Moreover, this invention provides a portable apparatus provided with the above-mentioned speaker system. A mobile phone is taken as an example of the mobile device.

  According to the present invention, in a computer program that causes a processing device to execute processing of an audio signal, processing for acquiring a sample of the audio signal, processing for obtaining an average spectrum of the sample, and a first band of the sample are output. A process of reducing the level to a predetermined level according to the output characteristics of the speaker, a process of obtaining the power of the sample after the level of the first band is reduced, and a second band different from the first band of the sample A computer program is provided that executes a process of amplifying the signal according to power.

  When an input corresponding to an output exceeding the power supply voltage is made to the speaker amplifier, distortion caused by the restriction of the power supply voltage, that is, a so-called clip occurs at the output of the speaker amplifier. By attenuating signals in a band that does not have a large effect and amplifying signals in a band that has a large effect on hearing, it is possible to increase the dynamic range of the band that has a large effect on hearing while avoiding the occurrence of clipping. As a result, the substantial dynamic range can be expanded.

  A mobile phone 100 according to an embodiment of the present invention will be described. Referring to FIG. 1, a mobile phone 1 includes a radio unit 1 that transmits and receives radio signals to and from a base station (not shown), an operation unit 2 that operates a mobile phone 100, a CPU 3 that performs various controls of the mobile phone 100, and a ring tone. Data ROM 4 storing voice data such as data and incoming melody data, sound source unit 5 that reads voice data from the data ROM 3 and outputs it to a DSP (Digital Sound Processor) 6, DSP 6 that performs equalizer processing on the incoming melody signal D / A converter 7 for converting digital data into analog data, A / D converter 8 for converting analog data into digital data, speaker amplifier 9 for increasing / decreasing the level of incoming melody, microphone amplifier for increasing / decreasing the level of microphone input signal 10. Sound ringing for incoming melody data A speaker 11 and a microphone 12 for inputting an audio signal are provided.

  The speaker 11 has a maximum allowable input signal level in the specification. The speaker amplifier 9 is provided with a limiter so that a signal level higher than the maximum allowable signal level is not input to the speaker 11. When the input signal to the speaker 11 exceeds the maximum allowable signal level of the speaker 11, the speaker amplifier 9 controls the clip so that a signal level larger than the maximum allowable signal of the speaker is not input to the speaker 11 by clipping the waveform. .

  Next, a process in which the mobile phone 100 sounds an incoming melody on the speaker 11 in response to an incoming call will be described. The user of the mobile phone 100 selects the incoming melody data to be sounded in response to the incoming call from the melody data stored in the data ROM 4 and sets it using the operation unit 2. The set value is stored in a memory (not shown) accessible from the CPU 3. In this state, when the wireless unit 1 receives a call from a base station (not shown) to the mobile phone 100, the CPU 3 detects an incoming signal. In response to this, the CPU 3 refers to the set value and instructs the sound source unit 5 to output the set incoming melody data. The sound source unit 5 reads out the corresponding incoming melody data from the data ROM 4 and outputs it to the DSP 6. The DSP 6 performs an equalizer process on the incoming melody data and outputs it to the D / A converter 7. The D / A converter 7 converts the incoming melody data from digital data to analog data and outputs it to the speaker amplifier 9. The speaker amplifier 9 adjusts the level of the incoming melody data converted into analog data and causes the speaker 11 to ring.

  Here, the equalizer process by the DSP 6 will be further described.

  Speakers built into portable devices are inevitably small and thin. In general, it is difficult to output such a speaker at a sufficient volume. As a technique for ensuring a sense of volume, it is conceivable to uniformly increase the input level of the entire audio signal band, but this technique improves the sense of volume but allows the maximum allowable speaker. Since the speaker amplifier electrically clips signals with a level exceeding the input signal, the output waveform is also clipped, and as a result, good sound quality cannot be obtained.

  The DSP 6 performs a process of attenuating the input level of the first band and amplifying the input level of the second band different from the first band. At this time, the attenuation level of the first band and the amplification level of the second band are set so that the power does not change before and after the equalizer process. Equalizing adjustment is performed so that the power reduced by attenuating the signal level of the first band is equal to the power increased by amplifying the signal level of the second band.

  For example, it is difficult to obtain a sound pressure characteristic at a low frequency particularly in a small and thin speaker as compared with a large-diameter speaker. For this reason, even if a low-frequency signal is attenuated by the above-described equalizer processing, a great difference in audibility does not occur. However, by attenuating the low-frequency signal level, the same effect can be obtained as when the dynamic range until the signal is clipped by the speaker amplifier is increased.

  Further, the input signal energy is optimally distributed to the speaker characteristics by amplifying the electric signal level of the second band so that the power before and after the equalizer processing becomes equal by the amount of attenuation of the signal level of the first band. be able to. For example, even with a small-diameter / thin speaker, it is possible to ensure a sense of volume without degrading the sound quality.

  A specific example of the equalizing process of the DSP 6 in the mobile phone 100 will be described with reference to FIG. In this example, the first band is a band of 600 Hz or less, and the second band is a band of 1000 Hz to 10000 Hz.

  In the equalizing process of FIG. 2, the low range of 600 Hz or less is attenuated as the frequency is lowered. In particular, the band of 300 Hz or less is greatly attenuated to -20 dB or less. Small and thin speakers cannot obtain sound pressure characteristics in the low frequency range compared to large-diameter speakers, so even if a low frequency signal of 300 Hz or less is attenuated by an equalizer, there is no significant difference in audibility. By attenuating the signal level, it is possible to obtain an effect of increasing the dynamic range until the signal is clipped by the speaker amplifier.

  On the other hand, in the middle range from 1000 Hz to 10000 Hz, the amplification level is gradually increased from 0 dB to about 5 dB, maintained at about 5 dB from 2000 Hz to 8000 Hz, and gradually decreased from 5 dB to 0 dB from 8000 Hz to 10000 Hz.

  In the present embodiment, an example in which a signal level in a low band of 300 Hz or less is particularly attenuated is shown. The frequency band in which sufficient sound pressure cannot be secured by the speaker varies depending on the speaker characteristics. For this reason, the band to be attenuated is selected according to the speaker characteristics.

  The present embodiment is an example in which the low band and the high band are the first band and the middle band is the second band. As shown in FIG. 3, in the equalizing process of the DSP 6 in the present embodiment, a process of attenuating a band of 600 Hz or less and two bands of 8000 Hz or more and amplifying a band of 1000 Hz to 8000 Hz is performed. It should be noted that the amplification level in the second band is higher than 5 dB in FIG. Thereby, the power is maintained before and after the equalizing process.

  Similar to the first embodiment, the equalizer characteristic in FIG. 4 significantly attenuates the signal level in the low band of 300 Hz or less. Small and thin speakers cannot obtain sound pressure characteristics in the low frequency range compared to large-diameter speakers, so even if a low frequency signal of 300 Hz or less is attenuated by an equalizer, there is no significant difference in audibility. By attenuating the signal level, it is possible to obtain an effect of increasing the dynamic range until the signal is clipped by the speaker amplifier.

  In this embodiment, the DSP 6 also attenuates the band from 8000 Hz to 20000 Hz. Compared to the low band, the attenuation level is small and is -10 dB at about 15000 Hz. In particular, in a piezoelectric ceramic speaker that has been reduced in thickness, the impedance decreases as the frequency of the ringing signal becomes higher, and the current consumption increases accordingly. However, when the high-frequency signal is reduced by the equalizer as described above, the current consumption of the speaker 11 when the signal is sounded can be reduced. At the same time, the dynamic range until clipping can be amplified by reducing the electrical signal level.

  Further, the DSP 6 amplifies the electric signal level in the band from 1000 Hz to 8000 Hz. The band to be amplified is determined based on the level of the harmonic component generated when the signal of the band is electrically clipped by the speaker amplifier 9 and ringed by the speaker 11. When the electric signal level is amplified by the speaker amplifier, distortion occurs due to electric clipping by the speaker amplifier, and there is a concern about deterioration of sound quality. However, in particular, in the case of a piezoelectric speaker, it has been confirmed that the level of the harmonics is small with respect to the fundamental wave when the signal after the mid-high range signal is electrically clipped by the speaker amplifier 9 is sounded. For this reason, in the case of a piezoelectric speaker, even if a harmonic is generated as a result of amplifying a signal in the middle and high range, it is possible to suppress deterioration in sound quality on hearing.

  This will be described in more detail with reference to the drawings. 4 and 5 show a sine wave signal having the same frequency as the spectrum component of the output of the speaker 11 when the sine wave signal of the maximum allowable input level of the speaker 11 is input to the speaker 11 via the speaker amplifier 9. It is the graph which compared with the spectrum component of the output of the speaker 11 when it inputs into the speaker 11 through the speaker amplifier 9 after 6dB amplification. In the former case, no clipping occurs in the speaker amplifier 9. In the latter case, clipping occurs. Here, the speaker 11 is a piezoelectric speaker.

  FIG. 4 is a graph when a 600 Hz sine wave signal is used as an example of the low frequency signal. In either case, the speaker 11 outputs a signal of 600 Hz as a fundamental wave and, as a harmonic component, 1200 Hz, 1800 Hz, 2400 Hz, 3000 Hz,... And a harmonic component having a frequency that is an integral multiple of the fundamental wave. Output. Looking at the harmonic components when clipping, it can be seen that especially the second and third harmonic levels are amplified and reach a level substantially equal to the fundamental wave. From this, it can be seen that clipping a low-frequency signal results in a very large deterioration in sound quality and gives a sense of distortion.

  On the other hand, FIG. 5 is a graph when a 2000 Hz sine wave is used as an example of the mid-range signal. In any case, the speaker 11 outputs a 2000 Hz signal as a fundamental wave, and outputs a harmonic component at a frequency that is an integral multiple of the fundamental wave, such as 4000 Hz, 6000 Hz, 8000 Hz,. ing. Comparing the fundamental and harmonic components with and without clipping, the harmonic level increased slightly when clipping occurred, but the harmonic level was sufficiently small relative to the fundamental level, resulting in a large sense of distortion. Don't give. As described above, even if the frequency components in the middle range or higher are amplified by an equalizer and the signal is electrically clipped by the speaker amplifier, the sound quality is not adversely affected in terms of hearing.

  In this way, the work of examining the level of the harmonic component generated when a signal of an electrically clipped frequency is sounded by the speaker 11 is performed over the entire output band of the speaker 11. As a result, since it is possible to know a band in which the sound quality does not deteriorate even if amplified and inputted to the speaker 11, the band to be amplified by the DSP 6 is determined based on this band.

  In the first and second embodiments, the first and second bands are fixed regardless of the input signal, and the DSP 6 amplifies and attenuates the signal level of a predetermined band. On the other hand, in the third embodiment, the input signal is sampled every predetermined interval, and the decrease in power by attenuating the signal level in the first band and the signal level in the second band are amplified. Signal processing is performed so that the increase in power caused by

  Signal processing executed by the DPS 6 in this embodiment will be described with reference to FIG. It is assumed that sound signal data such as a ringing melody is about to ring on the speaker 11.

  When signal data is input from the data ROM 4 to the DSP 6 via the CPU 2 and the sound source unit 5, the DSP 6 performs an analysis process of the average spectrum of the audio signal data for N samples (step S1).

  The band in which the sound pressure cannot be secured by the speaker 11 has been examined beforehand. This band is the first band. The first band is a low band of, for example, 300 Hz or less. The DSP 6 performs power calculation for the first band (step S2).

  The DSP 6 performs signal level reduction processing on the signal in the first band so that the equalizer characteristics as shown in FIG. 2 are obtained (step S3). For example, a 400 Hz signal is attenuated by 10 dB, and a 300 Hz signal is attenuated by 20 dB.

  Next, a calculation process is performed on the power after the signal level reduction process in step S3 (step S4).

  The band in which the sound pressure can be secured by the speaker 11 is also examined in advance, and this band is set as the second band. The signal level in the second band is amplified so that the power in the second band is increased by the same amount as the power decrease obtained in step S4 (step S5).

  After step S5, it is confirmed whether the melody ringing from the speaker 11 has ended. If the melody ringing has not been completed, the same processing is performed for the next N samples of melody, and the melody ringing has been completed. The process is terminated (step S6).

  As described above, by making the power attenuated in the first band reduction process equal to the power amplified in the second band amplification process, it is possible to avoid deterioration in sound quality due to electrical clipping. Good sound quality can be ensured and the volume can be improved. Further, the power reduction due to the first band level reduction is obtained, and the process of amplifying the second band level to compensate for the reduction is performed in real time based on the sampling data, so that the sound signal to be sounded Processing can be performed.

  While the present invention has been described with reference to the embodiment and examples, the present invention is not limited to this. For example, in the above description, a mobile phone has been described as an example. However, the present invention is not limited to this, and is particularly limited to small and thin speakers included in portable information devices, notebook computers, portable DVD players, and the like. Is suitable.

  In addition, compared with the case where the present invention is applied to a speaker system including an electromagnetic speaker, the case where the present invention is applied to a speaker system including a piezoelectric ceramic speaker is more effective. As shown in FIG. 7, the piezoelectric ceramic speaker has poor low-frequency characteristics and some peaks in the middle-high frequency characteristics as compared with the electromagnetic speaker, but the sound pressure is low overall and the sound quality is low.・ It is difficult to secure a sense of volume.

  Furthermore, the present invention is effective even for a speaker system including a speaker whose output sound pressure is large depending on the band and a speaker with high power consumption, not necessarily a small and thin speaker.

It is a functional block diagram of the mobile telephone 100 which is one embodiment of this invention. It is a graph for demonstrating the equalizing process which DSP6 performs in Example 1 of this invention. It is a graph for demonstrating the equalizing process which DSP6 performs in Example 2 of this invention. To compare the spectrum when a low-frequency signal (600 Hz) of the maximum allowable level is input and ringed by a speaker with the spectrum when the same signal is input while being clipped and ringed by a speaker It is a graph of. It is a graph for comparing the spectrum when the maximum allowable level mid-range signal (2000 Hz) is sounded by a speaker and the spectrum when the same signal is clipped and sounded by the same speaker. It is a flowchart for demonstrating the operation | movement of Example 3 which changes the attenuation level of a 1st zone | band and the amplification level of a 2nd zone | band according to the sampling result of an input signal, and performs each attenuation / amplification. It is a graph for demonstrating the difference in the sound pressure by the frequency of an electromagnetic type speaker and a piezoelectric ceramic speaker.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wireless part 2 Operation part 3 CPU (Central Processing Unit)
4 Data ROM (Read Only Memory)
5 Sound Source 6 DSP (Digital Signal Processor)
7 D / A (Digital / Analog Converter)
8 A / D (Analog / Digital Converter)
9 Speaker amplifier 10 Microphone amplifier 11 Speaker 12 Microphone 100 Mobile phone

Claims (10)

In the audio signal output method,
In a DSP (Digital Signal Processor), a decrease in power due to attenuation of the first band level and an increase in power due to amplification of a second band level different from the first band are applied to the audio signal. The audio signal that attenuates the level of the first band, amplifies the level of the second band, and performs the attenuation and amplification is predetermined for a speaker amplifier so as to be equal to each other. Stage 1 for signal processing not to exceed the maximum allowable input signal level;
Output method of the audio signal, characterized in that the audio signal subjected to the attenuation and amplification, and a step 2 output from the speaker through the speaker amplifier.   2. The audio signal output method according to claim 1, wherein the first band includes a band higher than the second band.   2. The audio signal output method according to claim 1, wherein the first band is determined according to a characteristic of the speaker. 2. The method of outputting an audio signal according to claim 1, wherein the step 1 includes:
Obtaining a sample of the audio signal;
Obtaining an average spectrum of the sample;
Reducing the first band of the sample to a predetermined level according to the output characteristics of the speaker;
Determining the power of the sample with a reduced level of the first band;
And amplifying the second band of the sample according to the power. In the speaker system,
For the audio signal, the first power reduction is caused by the first band level attenuation and the power increase by the second band level amplification different from the first band is equal to each other. Attenuates the band level, amplifies the second band level, and the attenuated and amplified audio signal does not exceed a predetermined maximum allowable input signal level for a speaker amplifier . DSP (Digital Signal Processor) that performs various signal processing,
Said speaker amplifier for amplifying an output of the DSP,
A speaker system comprising: a speaker driven by the speaker amplifier.   The speaker system according to claim 5, wherein the first band includes a band higher than the second band.   6. The speaker system according to claim 5, wherein the first band is determined according to characteristics of the speaker.   6. The speaker system according to claim 5, wherein the speaker is a piezoelectric ceramic speaker.   A portable device comprising the speaker system according to claim 5. In a computer program for causing a processing device to execute processing of an audio signal,
Processing to obtain a sample of the audio signal;
Processing to obtain an average spectrum of the sample;
A process of reducing the first band of the sample to a predetermined level according to the output characteristics of the output speaker;
Processing to determine the power of the sample after reducing the level of the first band;
A process of amplifying the second band so as to amplify the power of the second band different from the first band of the sample by the same amount as the power reduction amount. A computer program which causes a speaker amplifier to execute so as not to exceed a predetermined maximum allowable input signal level.

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