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JP2004151225

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DESCRIPTION JP2004151225
The present invention makes it easy for a listener to recognize a sound output from a speaker, in
particular, a sound in a frequency band of less than 1 kHz, without increasing the maximum
output voltage of the amplifier. A fast Fourier transform processing unit (FFT) 10 performs FFT
processing on a digital signal which is an original signal for voice output, and converts it into a
frequency domain signal. The modulator 21 creates a harmonic component (third harmonic) of
the original signal converted to the frequency domain signal. The signal strength changing units
30 and 31 respectively halve the strengths of the output signals of the FFT processing unit and
the modulator, and the adding unit 40 adds them after adjusting them to be signals of the same
time in time series. . The inverse fast Fourier transform processing unit (IFFT) 50 inversely
transforms the added frequency domain signal into a time domain signal. The output signal of
the IFFT processing unit is converted into an analog signal, amplified to an arbitrary amplitude
by the variable amplifier 70 and output as an audible sound from the speaker 80. [Selected
figure] Figure 1
PORTABLE TERMINAL DEVICE, AND ITS OUTPUT VOLUME INCREASE METHOD
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
portable terminal device having a speaker for voice and sound output, and a method of
increasing the output sound volume from the speaker. 2. Description of the Related Art In recent
years, portable terminal devices such as portable telephones are required to output sound in a
frequency band of less than 1 kHz such as human voice and tone (sound) from a built-in speaker
(micro speaker). It is done. However, in response to the demand for smaller size, lighter weight
and lower power consumption of the portable terminal device, the speaker itself (diaphragm) has
also been miniaturized, making it difficult to increase the sound pressure below 1 kHz, and
driving the speaker further. It is also difficult to increase the maximum output voltage supplied to
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the amplifier, and it is becoming increasingly difficult to increase the volume output from the
speakers. On the other hand, there has been proposed a technique which makes it possible to
reinforce low-pass components in the listener's (user's) sense of hearing by adding harmonic
components higher than the audible frequency to musical tone signals (for example, Patent
Document 1). [Patent Document 1] Japanese Patent Application Laid-Open No. 8-123421 (page
1-2, FIG. 1-2) [0005] The above-described conventional portable terminal device is built in It is
difficult to increase the output sound volume due to the structural (size) and power supply
voltage (amplifier maximum output voltage) restrictions for the speaker (micro speaker). The
object of the present invention is to use a characteristic configuration and method in the
technology of reinforcing the sound volume by adding harmonic components to the original
signal, so that the output from the speaker can be increased without increasing the maximum
output voltage of the amplifier. It is an object of the present invention to provide a portable
terminal device capable of making a listener easily recognize a certain sound, particularly a
sound in a frequency band less than 1 kHz, and a method of increasing the output sound volume.
A method for increasing the output sound volume according to claim 1 of the present invention
is a method for increasing the output sound volume from a speaker in a portable terminal device
having a speaker for audio / sound output, The odd-order harmonic component of the original
signal for output to the speaker is created by fast Fourier transform processing and modulation
processing, and the odd-order harmonic component is added to the original signal in the
frequency domain and then inverse fast Fourier transform processing is performed. The method
further includes the steps of: returning to the signal of the domain, supplying a signal obtained
by adding the odd harmonic component to the original signal returned to the time domain to the
speaker and outputting it as an audible sound. According to a second aspect of the present
invention, there is provided the output volume increasing method according to the first aspect,
wherein the odd harmonic component is a third harmonic component.
According to a third aspect of the present invention, there is provided the output volume
increasing method according to the first aspect, wherein the odd harmonic component is an odd
harmonic component of a plurality of different orders. I assume. According to a fourth aspect of
the present invention, there is provided an output volume increase method according to the first
or second aspect, wherein the intensity ratio of the original signal to the odd harmonic
component to be added is 1: 1. It is characterized by having set. According to a fifth aspect of the
present invention, in the output volume increasing method according to the first, second or third
aspect, the original signal and each of all the odd harmonic components to be added are added. It
is characterized in that the intensity ratio can be arbitrarily changed under the condition that the
intensity after addition becomes the same as the intensity of the original signal. A portable
terminal device according to a sixth aspect of the present invention is a portable terminal device
having a speaker for voice and sound output, wherein the original signal for output to the
speaker is subjected to fast Fourier transform processing to be converted into a signal in a
frequency domain. Fast Fourier transform means, modulation means for branching and inputting
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the output signal of the fast Fourier transform means, and generating an odd harmonic
component of a predetermined order, an output signal of the fast Fourier transform means, and
an output of the modulation means Intensity changing / adding means for adding signals
according to a predetermined intensity ratio, inverse fast Fourier transform means for
performing inverse fast Fourier transform processing on an output signal of the intensity
changing / adding means, and the inverse fast Fourier transform means The output signal of the
conversion means is converted into a signal capable of outputting an audible sound from the
speaker, amplified, and signal conversion / amplification means for supplying the speaker Ru. A
portable terminal device according to claim 7 of the present invention is characterized in that, in
the portable terminal device according to claim 6, the modulation means generates a third
harmonic component as the odd harmonic component. Do. A portable terminal device according
to an eighth aspect of the present invention is the portable terminal device according to the sixth
aspect, wherein the modulation means includes a plurality of corresponding to odd-order
harmonic components of a plurality of different orders designated in advance. The intensity
change / addition means adds the output signal of the fast Fourier transform means and the
output signal of each of the plurality of modulation means in accordance with a predetermined
intensity ratio. A portable terminal device according to claim 9 of the present invention is the
portable terminal device according to claim 6 or 7, wherein the intensity changing / adding
means is an output signal of the fast Fourier transform means, and of the modulation means. It is
characterized in that the intensity ratio with the output signal is added as 1: 1.
A mobile terminal device according to a tenth aspect of the present invention is the mobile
terminal device according to the sixth, seventh or eighth aspect of the present invention, wherein
the intensity changing / adding means adds all to the output signal of the fast Fourier transform
means The intensity ratio to the output signal of each of the modulation means can be arbitrarily
changed under the condition that the intensity after addition becomes the same as the intensity
of the original signal. BEST MODE FOR CARRYING OUT THE INVENTION First, the outline of the
present invention will be described. The mobile terminal device according to the present
invention adds a harmonic component to the original signal (fundamental frequency) to output
the sound volume (sound volume in the sense of hearing) output from the mobile terminal builtin micro speaker without increasing the maximum output voltage of the amplifier. It is a portable
terminal device that can raise More specifically, the mobile terminal device buffers a digital
signal such as an audio signal or an acoustic signal in the time domain sent from the
demodulator for an arbitrary number of seconds and then performs FFT (Fast Fourier) at an
arbitrary score. Transform (Fast Fourier Transform) processing is performed to transform the
signal into a frequency domain signal. The signal after conversion is divided into two (or two or
more), one performs only the signal strength change processing as an original signal, and the rest
is a harmonic component for each predetermined order (odd number: for example, third order,
fifth order) A creation process (modulation process) and a signal strength change process are
performed. The signal component which went out of band by modulation is deleted. The original
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signal (basic frequency component signal) after signal strength change processing and its
harmonic component signal are adjusted so as to become signals of the same time in time series
and then added, and the frequency domain signal of the addition result is subjected to FFT
processing The inverse FFT processing is executed with the same score as the score obtained to
convert it into a time domain signal and further convert it into an analog signal. This analog
signal is amplified to an arbitrary amplitude and then output from a speaker (micro speaker).
Next, embodiments of the present invention will be described in detail with reference to the
drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, showing
only the part related to the present invention in the portable terminal device. In FIG. 1, the
portable terminal device 1 of this example is used as a portable telephone which is a mobile
station of a mobile communication system, and is used as an output means for voice and acoustic
information to a user. 10), the modulator 21, the signal strength change units 30, 31, the
addition unit 40, the inverse fast Fourier transform processing unit (IFFT) 50, the digital / analog
converter (DAC) 60, the variable amplifier 70, and , And a speaker 80.
Although not shown, the mobile terminal 1 transmits and receives radio signals between a voice
input unit that includes a microphone and inputs voice information from the user, and wirelessly
performs modulation / demodulation of voice signals. It has a unit, an operation display unit for
inputting and displaying character and graphic information for the user, and a control unit for
controlling the entire apparatus. The fast Fourier transform processing unit (FFT) 10 is
connected to a demodulator of a wireless unit (not shown), and high-speed signals are outputted
from the demodulator (digital voice signal: PCM (Pulse-Code Modulation) signal) A Fourier
transform process (FFT: Fast Fourier Transform) is performed, and the signal after the FFT
process is divided into two and sent to the modulator 21 and the signal strength change unit 30,
respectively. The modulator 21 modulates the frequency of the signal output from the fast
Fourier transform processing unit 10 to an odd multiple (here, triple) and sends it to the signal
strength change unit 31. The signal strength changing unit 30 changes (in this case, 0.5 times)
the strength of the signal output from the fast Fourier transform processing unit 10 and sends it
to the addition unit 40. The signal strength changing unit 31 changes (in this case, 0.5 times) the
strength of the signal output from the modulator 21 and sends it to the adding unit 40. The
adding unit 40 adds the output signal of the signal strength changing unit 30 and the output
signal of the signal strength changing unit 31 and sends the result to the inverse fast Fourier
transform processing unit (IFFT) 50. The inverse fast Fourier transform processing unit (IFFT) 50
performs inverse FFT processing on the signal output from the addition unit 40, and sends the
processed signal to a digital / analog converter (DAC) 60. The digital / analog converter (DAC) 60
converts the digital signal output from the inverse fast Fourier transform processing unit 50 into
an analog signal and sends it to the variable amplifier 70. The variable amplifier 70 amplifies the
signal output from the digital / analog converter 60 by an arbitrary amplification factor and
sends the amplified signal to the speaker 80. The speaker 80 emits voice and sound according to
the input signal, and can be listened to by the user. Next, the operation of this embodiment will
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be described in more detail. The fast Fourier transform processing unit (FFT) 10 buffers the
digital signal (PCM signal) sent from the demodulator (not shown) for an arbitrary number of
seconds (for example, 20 ms) and then performs FFT processing at an arbitrary score. And
convert the signal to a frequency domain signal.
The score mentioned here corresponds to the accuracy when converting the input signal into the
frequency domain by the FFT processing. For example, if a 256-point FFT is performed on an
input signal with a sampling frequency of 8 kHz, the frequency distribution of the input signal
can be obtained in (4000/256) Hz steps. Alternatively, if a 128-point FFT is performed on an
input signal with a sampling frequency of 16 kHz, the frequency distribution of the input signal
can be obtained in (8000/128) Hz steps. Generally, the number of points to be selected (points
suitable for FFT processing) is 128, 256, 512, 1024, 2048 points. In the case of this example, it
is 128 points. The signal converted into the frequency domain signal is sent to the modulator 21
and the signal strength changing unit 30. The modulator 21 modulates the frequency of the
received signal so as to be tripled to create a harmonic component (third harmonic) of the
original signal, and the processed signal is sent to the signal strength changing unit 31. send. The
signal component which went out of band by modulation is deleted. The reason for the triple is
that the post-processing signal is the lowest order harmonic component that is not likely to make
human (user) uncomfortable, and it should not be an even multiple as it makes human
uncomfortable. The signal strength changer 30 and the signal strength changer 31 respectively
halve the strength of the input signal and send it to the adder 40. The reason for halving is to
prevent the signal strength from exceeding the digital maximum value when adding two signals
in the adding unit 40. The addition unit 40 adjusts the output signals of the signal strength
change unit 30 and the signal strength change unit 31 so as to become signals of the same time
in time series, and then adds them, thereby performing an inverse fast Fourier transform
processing unit (IFFT ) Send to 50. The inverse fast Fourier transform processing unit 50
performs inverse FFT processing on the input frequency domain signal with the same score (128
points in this example) as the score executed by the fast Fourier transform processing unit 10.
Convert to time domain signals and send to digital to analog converter (DAC) 60. A signal output
from the inverse fast Fourier transform processing unit 50 is converted to an analog signal by a
digital / analog converter (DAC) 60, amplified to an arbitrary amplitude by a variable amplifier
70, and then audible sound from the speaker 10. Is output as As described above, in the present
embodiment (first embodiment), the input signal (original signal) and the third harmonic
component added to the input signal have an intensity ratio of 1: 1 It is added so that the
intensity after 0.5: 0.5) and addition becomes the same as the input signal intensity (1 = 0.5 +
0.5).
Next, a modification of the first embodiment will be described. The amplification factor of the
signal strength changing part 30 and the amplification factor of the signal strength changing
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part 31 shown in FIG. 1 are changed to any amplification factor as long as the sum of the
amplification factors of both satisfies the condition “1”. It does not matter (for example, 0.7
and 0.3). Thereby, the intensity of the harmonic component can be adjusted arbitrarily. Further,
the modulation amount of the modulator 21 may be changed to an arbitrary modulation amount
(for example, 5 times) as long as the condition of odd multiple is satisfied. Next, another
embodiment (second embodiment) of the present invention will be described with reference to
FIG. The portable terminal device 2 of the second embodiment shown in FIG. 2 differs from the
portable terminal device 1 of the first embodiment shown in FIG. 1 in the addition of the fast
Fourier transform processing unit (FFT) 10 A modulator 22 and a signal strength changer 32
connected in series with each other are added to the unit 40, and the amplification factor of the
signal strength changer 31 is changed to 0.25. The modulator 22 modulates the frequency of the
signal output from the fast Fourier transform processing unit 10 by 5 times and sends it to the
signal strength change unit 32. The signal strength changing unit 32 multiplies the signal output
from the modulator 22 by 0.25 and sends it to the adding unit 40. This can increase the degree
of freedom of combination of harmonic components. The functions and operations of the other
parts are the same as those of the portable terminal device 1 shown in FIG. Next, a modification
of the second embodiment will be described. In FIG. 2, the amplification factor of each of the
signal strength changing units 30, 31, and 32 may be changed to any amplification factor as long
as the sum of the amplification factors of three parties satisfies “1”. (E.g. 0.5, 0.3 and 0.2).
Thereby, the intensity of the harmonic component can be adjusted arbitrarily. Further, although
the number of sets of the modulator and the signal strength changing unit added in FIG. 2 is one,
any number may be added. However, the modulation rate must be an arbitrary odd multiple (3
times, 5 times, 7 times, etc.), and the sum of the intensity amplification rates of all the signal
intensity changing parts must be “1”. In each of the above-described embodiments, the
portable terminal device is a portable telephone, but the present invention is not limited to this,
and any portable terminal device having a speaker for voice and sound output may be used. It is
applicable. For example, a radio, a recorder / player, or a song player can be considered.
As described above, according to the present invention, since the harmonic component of the
output signal is added to the original signal, the signal strength before amplification by the
amplifier can be increased, and the maximum amplitude of the amplifier can be increased. It is
possible to increase the volume of the sound output from the speaker without increasing the
output voltage. In addition, even when a microspeaker that can not increase the sound pressure
below 1 kHz is used as a speaker, the sound component of 1 kHz or more that can increase the
sound pressure increases even with the microspeaker, making it difficult for the listener to
recognize in the prior art. It is possible to easily make the listener recognize sounds less than 1
kHz (the fundamental frequency). BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block
diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing
another embodiment of the present invention. [Description of the code] 1, 2 Mobile terminal
device 10 Fast Fourier transform processing unit (FFT) 21, 22 Modulators 30, 31, 32 Signal
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strength changing unit 40 Addition unit 50 Inverse Fast Fourier Transform processing unit (IFFT)
60 Digital / Analog converter (DAC) 70 Adjustable amplifier 80 speaker
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