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Description 1 Title of Invention
Signal processing device for headphones
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal
processing apparatus for performing three-dimensional reproduction with a headphone, and in
particular, to obtain a feeling of front foot position. In sound reproduction with a conventional
headphone, it is general to supply stereo signals for the speaker as it is to the right and left
reproduction devices of the headphone. l: The listening window in the case of town life, the sound
image is near the ears and between both ears sound image does not leave the head listening to in
the sound field / fm 'IQ, is unnatural compared to the feeling, listening fatigue There was a
drawback to Also, in order to eliminate any of the above-mentioned drawbacks, in the case of
reproduction by a speaker, sounds other than the reproduction sound on each ear side which the
listener receives on each ear 1d, An apparatus has been previously proposed that adds reflected
sound or the like from a room wall or the like to each channel as a crosstalk signal or a delay
signal. However, even with these devices, although the sound image is localized outside the head
and EndPage: 1 has a relatively natural sense of spread from side to side, the sound image is
generated above the head and no forward spread feeling is obtained at all. It did not become the
most natural sense of localization as in the case of so-called speaker reproduction. Therefore, in
the present invention, it is an object of the present invention to obtain a three-dimensional sound
reproducing apparatus using a headphone which can obtain a sense of forward localization in
addition to the sense of outside localization as described above. Hereinafter, the present
invention will be described based on an embodiment shown in the drawings. In general, the
human 1 grasps the incident direction of sound three-dimensionally (left, right, up, down, front
and back), and the sense of right and left among these is represented by the time difference and
level difference generated in both ears when the sound wave reaches the head. It is well known
that it is perceived by the difference between the two ears. On the other hand, with respect to
direction perception regarding upper and lower, front and back, waveform distortion (spectral
change including phase) due to the auricle is the main physical factor. Describing this waveform
distortion in detail, as shown in FIG. 1, the sound pressure response frequency amplitude
characteristics at the entrance of the ear canal as shown in FIG. Become. Here, FIG. 2 a is a
characteristic of the right ear and FIG. 2 is a characteristic of the left ear. According to FIGS. 2a
and 2b, it can be seen that a rise in sound pressure around 3 to 6 KHz and a characteristic dip
occur around 8 = IOKH2, but among these, those defining the incident angle in perception are
mainly It is considered to be the frequency position of the latter dip. This tip is considered to be
caused by phase interference based on the reflection of the auricle, and such a body is
approximately modeled as shown in FIG. 3 and reflected by the sound d directly incident on the
ear canal 1 and the auricle 2 Indicated by the sound e.
And if this is shown with an equivalent circuit, it will become like FIG. In FIG. 4, the sound
incident on the input line 3 is branched into a line corresponding to the direct sound added to
the adding portion 7 directly and a line corresponding to the reflected sound passing through the
delay circuit 5, and the signal passed through the delay circuit 5 is Through the resistance 6
corresponding to absorption by the auricle, it is added in the addition part 7 and is heard as the
ear input 4. From the above, when listening to a stereo signal for a speaker by a headphone, a dip
corresponding to the characteristic of FIG. 2 obtained experimentally is obtained to obtain a
feeling of forward localization similar to a general sound field. It turns out that it is sufficient to
process the stereo signal for the speaker and add it to the headphone so that the characteristic
can be obtained. As to the specific signal processing, it can be understood from the equivalent
circuit of FIG. 4 that it can be approximately obtained by adding a signal having an appropriate
delay time to the original signal. However, since the tip characteristics shown in FIG. 2 are
different depending on the structure of the auricle, there are individual differences, and even the
same person differs between both ears, so a circuit for processing a signal is configured. In order
to match the characteristics of each individual, it is necessary that the left and right channels be
provided independently and be arbitrarily adjustable. Here, it is sufficient to have a range in
which the frequency position of the above-mentioned dip can be varied as long as about 7 to 13
KH 2, and if the tip depth is about 10 to 20 dB − experimentally proved to be adapted to most
people There is. Next, means for processing the signal for the speaker for the headphone based
on the above experimental results will be specifically described. FIG. 5 shows an embodiment of a
dip circuit for obtaining characteristics approximate to the dip characteristics as shown in FIG. 2
which is constructed based on the equivalent circuit of FIG. In the figure, reference numeral 8 is
an input line, and a signal applied to the input line 8 is branched into two, one of which is added
to an attenuator 10 having an attenuation ratio through a delay circuit 9 having a delay amount
Δ and attenuated to an appropriate level. After being added, it is added to the direct signal
through the other line at the addition portion 11 and taken out to the line 12 as an output. Here,
assuming that the transfer function T (,) ω of this dip circuit is τ (d) −no + Ke ′ ′ ′ ′ ′,
the amplitude term IT (jω) Iil−iEndPage: 2m−) 1 ≦ box q 沫 E 弔It becomes (pi)-+ I---(J).
However, if an appropriate delay time Δt is given to this equation, a frequency characteristic
having a dip at 26 t [H 2] can be obtained. FIG. 6 is a frequency characteristic diagram when the
delay time .DELTA.t of the circuit of FIG. 5 is 50 .mu.sec and the attenuation ratio K is 07 (-3aB),
and a dip of 15 dB in depth occurs at a position of 10 kHz.
From the above, it is possible to easily change the position of the dip by changing the delay time
Δt of the delay circuit 9 using the circuit of FIG. 5, and to change the attenuation ratio k of the
attenuator IO. Since the depth of the tip can be adjusted accordingly, it is possible to process the
signal in accordance with the dip characteristics of the individual's ear. FIG. 7 is a block diagram
showing an embodiment for obtaining a more specific three-dimensional effect of the threedimensional sound reproducing apparatus according to the present invention, wherein a signal
for a speaker cut into two input lines I3 and I3 'is The crosstalk circuit 14 gives crosstalk
corresponding to the diffracted sound of the head, and the dip circuit 15.15 'as shown in FIG. 5
provided on each line gives a dip for forward localization. , And an indirect sound addition circuit
provided in parallel with the circuit for giving a direct sound, which is branched from the input
line 13.13 'and is added to each reproduction unit of the headphone 17 as an output
corresponding to a direct sound. A signal corresponding to a sound or a reverberation
component is configured to be given to the heddle horn 17. Here, to explain the both-ears open
cover r, as illustrated in FIG. 8, when a sound is emitted from the front speaker 20 having an
angle of α with respect to the median plane 19 of the listener 18, Let the sound incident on the
near ear 18a be P (ω), the other ear 1 '81) has a time difference Δt with the level difference
function k (ω) and a signal k (ω) e-306t- Since P (ω) is given, the signal processing
corresponding to this time difference is performed as shown in FIG. 9 with filters 21, 2.1 ′
having transfer functions k (ω) in the other channels. The signal may be forced through the
delay circuit 22.22 'having a delay time of .DELTA.t. Next, the indirect sound will be described.
The indirect sound can be divided into a single reflection sound and a reverberation component,
and the reflection sound is separated from the direct sound in a directional manner, has a delay
time, and has level attenuation (the attenuation is frequency And can be obtained by using the
reflected sound addition circuit shown in FIG. 1θ. In FIG. 9, 23. . Reference numeral 23 'is a filter
corresponding to the spectral ratio to the direct sound, and a low pass filter with a cutoff
frequency of 1 kHz' 1 slope 60 dB 10 CT is suitable. 24a and 24b are delay circuits
corresponding to the delay time relative to the direct sound of the reflected sound, and it is best
to give a delay in the range of 10 to 30 m5 ec, if the delay times between the two channels, ie
24a and 24b, are different Need to
25.25 'is a filter of the level difference function that occurs in both ears when the reflected sound
is incident, and 26.26' is a delay circuit corresponding to the time difference between both ears
when the reflected sound is incident, In this reflected sound addition circuit, there is provided a
line 27. 27 'for directly applying signals to the final stages of the other channels from the
subsequent stage of the delay circuits 24a and 24b. FIG. 1 is a block diagram showing a
reverberation component addition circuit. In FIG. 1, a reflected sound sequence is obtained by
feedback, and this is added. In the figure, 31: 31 'is a delay circuit which gives a time interval ΔT
between each reflected sound, and 28. 28' is a level attenuator which gives a level ratio between
each reflected sound. 2'9.29 'is a filter corresponding to the spectral difference from the direct
sound, and 30 is a phase inverting circuit which makes both channels be in opposite phase to
each other. Therefore, according to the present invention, the following effects can be obtained
by the above-mentioned configuration. (1) A steep band between 7 and 13 kHz of the frequency
characteristic; A tip filter circuit having a dip of about 0 to 10 (iB is provided in the signal
processing apparatus for the headphone, so that the head j and 2-nd listen This gives you a sense
of listening that is localized in front of the listener, and gives you a more natural listening
experience like listening through a speaker. EndPage: 3 (2) The above-mentioned tip filter circuit
is inserted in each line which supplies signals to the two reproduction units of the headphone in
the signal processing device, and can independently vary the dip frequency position. By doing
this, it is possible to select the characteristics suitable for each individual listener using the signal
processing device for the headphone, and it is possible to cause all persons to have a sense of
forward localization.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the direction of arrival of sound in the
median plane to the listener. FIG. 2 is a graph showing the actual sound pressure frequency
characteristics measured at the entrance of the ear canal in the state of FIG. 1, wherein FIG. 2 a
shows that of the right ear and b shows that of the left ear. Fig. 3 is a model of the reflection
effect by the auricle. FIG. 4 is an equivalent circuit of FIG. FIG. 5 is a tip circuit for giving dip
characteristics as shown in FIG. 2 made based on FIG. FIG. 6 is a tip characteristic diagram
obtained by the circuit of FIG. FIG. 7 is a block diagram of a circuit for converting a speaker
signal into a headphone stereo sound signal. FIG. 8 is a diagram for explaining the binaural
system. FIG. 9 is a block diagram of a crosstalk circuit. FIG. 10 is a block diagram showing a
single reflection sound addition circuit. FIG. 11 is a block diagram showing a reverberation
component addition circuit. 9 Delay circuit 10 Attenuator 14 Crosstalk circuit 15.15 'Dip circuit
6 Indirect sound addition circuit 10 "10" tagy H, r10 "EndPage: 4 Fig. 5 J1 (KHzl Fig. 9 End Page:
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