JPS6029280B2 - Signal processing device for headphone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal processing device for stereoscopic reproduction using headphones, and particularly to a signal processing device that provides a sense of standing in front.

When reproducing sound using conventional headphones, it is common to supply the stereo signals for the speakers as they are to the playback devices on the left and right sides of the headphones. This had the disadvantage that the sound image was generated near the ears or between both ears, and the sound image remained stuck in the head, making it unnatural compared to the listening experience in a real sound field, and causing listening fatigue.

In addition, in order to eliminate the above-mentioned drawbacks as much as possible,
In the case of playback by force, sounds other than the reproduced sound on each ear side that the listener receives in each ear, such as sounds diffracted from the head and sounds reflected from room walls, etc., are used as crosstalk signals or delayed signals. Devices for adding to each channel have previously been proposed.

However, even with these devices, although the sound image is localized outside the head and the feeling of spreading to the left and right becomes relatively natural, the sound image is generated above the head and does not give the feeling of spreading forward at all, which is different from what is called reproduction by speakers. It did not give the most natural standing feeling as in the case. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a three-dimensional sound reproduction device using headphones that provides a sense of standing in front of the head in addition to the above-mentioned sense of standing outside the head. Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

Generally, humans understand the direction of sound incidence three-dimensionally (left/right, up/down, front/back), and the left/right sense of direction is expressed by the time and level differences that occur between the ears when sound waves reach the head. It is well known that perception is based on interaural differences. On the other hand, waveform distortion (spectral change including phase) caused by the ear shell is the main physical factor for directional perception regarding up-down and front-back directions.

To explain this waveform distortion in detail, as shown in Figure 1, when a sound wave enters the head from the front in the median plane, the sound pressure and response frequency amplitude characteristics at the entrance of the external auditory canal are
The result will be as shown in the figure.

Here, FIG. 2a shows the characteristics of the right ear, and FIG. 2b shows the characteristics of the left ear. According to Figure 2 a and b, it can be seen that the sound pressure increases around 3 to shoe HZ and a characteristic dip occurs around 8 to 10 KH2, but among these, what determines the incident sense in perception is It is thought that this is mainly due to the frequency position of the latter dip. This dip is thought to be caused by phase interference based on reflections from the ear canal, and its appearance can be approximately modeled as shown in Figure 3.
This is represented by the sound d that is directly incident on the ear and the sound e that is reflected by the ear shell 2.

This is shown in an equivalent circuit as shown in 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 direct addition section 7 and a line corresponding to the reflected sound passing through the delay circuit 5, and the signal passing through the delay circuit 5 is The sum is added at the adding section 7 through a resistor 6 corresponding to the amount absorbed by the ear shell, and is heard as the ear input 4. Based on the above, when listening to stereo signals for speakers using headphones, in order to obtain a sense of standing in the front similar to that in a general sound field, it is necessary to use a dip corresponding to the experimentally obtained characteristics shown in Figure 2. It turns out that all you have to do is process the stereo signal for the speakers to obtain the desired characteristics and then add it to the headphones.

It can be seen from the equivalent circuit of FIG. 4 that the specific signal processing can be approximately accomplished by adding a signal having an appropriate delay time to the original signal.
However, the dip characteristics shown in Figure 2 vary depending on the structure of the ear shell, and therefore vary from person to person, and differ between both ears even in the same person. Therefore, when configuring a circuit for processing signals, must be provided independently for both the left and right channels in order to match the characteristics of each individual, and must be able to be variably adjusted as desired.

Here, the range for varying the frequency position of the dip is from 7 to
It has been experimentally found that a dip depth of about 10 to 2 days is sufficient, and most people can adapt to it if the dip depth is about 10 to 2 days. Next, means for processing signals for speakers for use in headphones will be specifically explained based on the above-mentioned experimental results. FIG. 5 shows an embodiment of a dip circuit constructed based on the equivalent circuit of FIG. 4 to obtain characteristics approximate to the dip characteristics shown in FIG. 2. In the figure, 8 is an input line, and the signal applied to the input line 8 is branched into two, one of which is attenuated through a delay circuit 9 with a delay amount Δt, and an attenuator 101 with a delay amount k, which attenuates the signal to an appropriate level. After that, it is added to the direct signal that has passed through the other line in an adding section 11, and taken out as an output on a line 12. Here, the transfer function T(j) of this dip circuit is
Then, T(j's) d10Ke-j's △t, and the amplitude term -T(jw)l is
It becomes {1}.

Therefore, if we give an appropriate delay time △t to this equation, Hiroshi [
HZ], a frequency characteristic with a dip can be obtained. Figure 6 is a frequency characteristic diagram when the delay time △t of circuit 0 in Figure 5 is selected to be 50 fsec, and the attenuation ratio k is 0.7 (1X old). A dip of B has occurred. From the above, the detap position can be easily varied by varying the delay time Δt of the delay circuit 9 using the circuit shown in FIG. 5, and the attenuation ratio k of the attenuator 10 can be varied. Since the depth of the dip can be adjusted by this, it is possible to process the signal in accordance with the dip characteristics of the individual's ear. 0 FIG. 7 is a block diagram showing an embodiment of the present invention. In order to obtain a more specific three-dimensional effect, in addition to the dip filter circuit of the present invention, a crosstalk circuit 14 and an indirect sound addition circuit 1 are used.
6.

In the figure, 15 and 15' are the dip circuits mentioned above,
It has the characteristics shown in Fig. 6, which corresponds to the dip in the transmission frequency characteristics caused by phase interference based on the reflection of the auricular shell of the ear. A circuit as shown in is constructed by well-known means, and the frequency position of the dip is between 7 and 1 Hz.
It is configured so that it can be set arbitrarily for each channel. Two input lines 13,1
3' is given crosstalk corresponding to head diffraction sound by a crosstalk circuit 14, and dip circuits 15, 15' as shown in FIG. 5 provided on each line. A circuit that provides a dip for forward localization is applied to each reproduction unit of the headphone 17 as an output corresponding to the direct sound, while a circuit that provides the above-mentioned direct sound is branched from the input lines 13 and 13'. An indirect sound adding circuit provided in parallel with the headphone 17 is configured to provide signals corresponding to reflected sound and reverberation components to the headphone 17.

Here, to explain the interaural difference, as illustrated in FIG. The sound incident on the near ear 18a is P (mountain).
Then, the other ear 18b receives a signal k (of) e' having a signal difference function k (mountain) and a time difference Δt, Δt・P (mountain).
As shown in FIG. 9, the signal processing corresponding to this time difference is performed using filters 21, 21' and △ which have transfer functions k (mountains) in the other channels.
The signal may be applied through delay circuits 22 and 22' having a delay time of t.

Next, to explain indirect sound, indirect sound can be divided into single reflected sound and reverberant components. Reflected sound is directionally separated from direct sound, has a delay time, and has a level attenuation (the degree of attenuation is determined by the frequency function), and the 10th
This can be obtained using the reflected sound adding circuit shown in the figure.

In Fig. 9, 23 and 23' are filters corresponding to the spectral ratio with the direct sound, and the cutoff frequency IKH
2. A low-pass filter with a slope of 6WB/OCT is suitable. 24a and 24b are delay circuits corresponding to the delay time of the reflected sound with respect to the direct sound, and it is best to provide a delay in the range of 10 to 3 hsec.The delay time between the two channels, that is, the delay time of 24a and 24b is It needs to be different.

25 and 25' are filters for the level difference function that occurs between both ears when reflected sound is incident, and 26 and 26' are delay circuits corresponding to the time difference between both ears when reflected sound is incident.
In this reflected sound addition circuit, delay circuits 24a and 24b
Lines 27 and 27' are provided for directly applying signals from the latter stage to the final stages of the other channels.

FIG. 11 is a block diagram showing the reverberation component addition circuit,
By applying feedback, a reflected sound series is obtained and added to it.

In the figure, 31 and 31' are delay circuits that provide a time interval ΔT between each reflected sound, and 28 and 28' are level attenuators that provide a level ratio between each reflected sound. Reference numerals 29 and 29' are filters corresponding to the spectral difference from the direct sound, and 30 is a phase inversion circuit that makes the two channels have mutually opposite phases.

Therefore, in this invention, the following effects can be obtained by configuring as described above.

{1- A steep 10~ frequency characteristic between 7~1st round HZ
By installing a dip filter circuit with a dip of approximately 2.2 in the headphone signal processing device, it is possible to obtain a listening sensation in which the sound image when listened to through headphones is localized in front of the listener. You can get a more natural listening sensation similar to listening through speakers. {2- By inserting the above-mentioned dip filter circuit into each line that supplies signals to the two reproduction units of the headphone in the signal processing device, the frequency position of each dip can be varied independently. It is possible to select characteristics suitable for each individual listener using a headphone signal processing device, and it is possible to make everyone feel a sense of forward localization.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the direction in which sound reaches the listener in the median plane. FIG. 2 is an actual sound pressure frequency characteristic diagram measured at the entrance of the external auditory canal in the state shown in FIG. 1, where a shows the right ear and b shows the left ear. Figure 3 is a model of the reflection effect caused by the ear shell. FIG. 4 is an equivalent circuit of FIG. 3. FIG. 5 shows a dip circuit that is created based on FIG. 4 and provides dip characteristics as shown in FIG. 2. FIG. 6 is a dibb characteristic diagram obtained by the circuit of FIG. 5. FIG. 7 is a block diagram showing an embodiment of the invention. FIG. 8 is a diagram for explaining the interaural difference. FIG. 9 is a block diagram of the crosstalk circuit. FIG. 10 is a block diagram showing a single reflection sound adding circuit. FIG. 11 is a block diagram showing a reverberation component adding circuit. 9...Delay circuit, 10...
・Attenuator, 14... Crosstalk circuit, 15,
15'... dip circuit, 16... indirect sound addition circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Claims] 1. In a two-channel signal line that supplies a speaker signal to a headphone that can be reproduced as sound by supplying it to a speaker, the difference in the transmission frequency characteristic caused by phase interference based on reflection from the ear shell. 1. A signal processing device for a headphone, characterized in that a dip filter circuit having characteristics corresponding to a dip and having a steep dip between 7 and 13 KHz is provided on the signal line. 2 In a two-channel signal line that supplies a speaker signal to a headphone that can be reproduced as sound by supplying it to a speaker, a characteristic corresponding to a dip in the transmission frequency characteristic caused by phase interference based on reflections from the ear shell is detected. A dip filter circuit having a steep dip between 7 and 13 KHz is provided on each of the two channel signal lines, and characteristic variable means provided in each of the dip filter circuits allows the frequency position of the dip to be varied between 7 and 13 KHz. 1. A signal processing device for a headphone, characterized in that each signal processing device can be independently varied between the two. 3 The depth of the dip filter circuit is -10d.
2. The headphone signal processing device according to claim 1, wherein the headphone signal processing device is configured such that the signal processing time is equal to or less than b. 4 The depth of the dip filter circuit is -10d.
The signal processing device for a headphone according to claim 2, wherein the signal processing device is configured such that the signal processing time is equal to or less than b.