Apparatus and method for automatic equalization of personal multi-channel audio system

An apparatus for automatically equalizing a personal multi-channel audio system, and a method therefor, are disclosed. White noises which are generated by a transfer characteristic measuring section are reproduced through speakers. Transfer signals from the respective speakers are collected through a microphone array at a listening position so as to transmit the collected signals to a transfer function calculating section. The transfer function calculating section calculates the transfer characteristics between the respective speakers and the listening position by utilizing the white noise and the collected signals. Then the sound characteristics of the respective sound channels are adjusted so that the transfer characteristics between the respective speakers and the listening position would be equalized. Further, phantom channels are synthesized and reproduced by utilizing the transfer functions and the installed speakers. Therefore, at the given environment, an optimum sound reproduction is obtained. Further, a small number of speakers can give an effect of a large number of speakers through the synthesis of phantom channels. In the case of an A/V system, the sound reproduction range can be adjusted in accordance with the size of the screen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for automatically equalizing 
a personal multi-channel audio system, and a method therefor. In 
particular, the present invention relates to an apparatus for 
automatically adjusting an audio reproducing characteristics, in which 
various parameters of a high fidelity personal or home using audio system 
are measured, and based on the measurement, the reproduction 
characteristics are corrected, and a phantom channel is formed, thereby 
automatically equalizing the reproduction environment. 
2. Description of the Preferred Embodiment 
Generally, the current audio systems adjust the sound volume and the 
balance. 
In the conventional audio systems, the difficulties encountered in the 
manual sound balance adjustment are overcome in such a manner, that the 
sound balance is automatically adjusted by adjusting volume and delays 
using the sound detected at the listening position, and that the sound 
balance, bass and treble are adjusted by proper selections on the part of 
the user in between two predetermined limits pausing at each intermediate 
value. 
Further, the currently used personal and home using audio systems are fixed 
to predetermined reproduction characteristics. That is, they imitates the 
reproduction atmosphere of theaters and public performance rooms. However, 
if a good listening environment is not provided, the audio system cannot 
give a good result. That is, in the case of a stereo sound, if the 
listening position and the two speakers do not form an equilateral 
triangle, then the sounds lean to one speaker, with the result that the 
stereo characteristics are degraded. Further, in accordance with the 
listening environment, the characteristics of the reproduced sounds are 
varied, and therefore, the optimum sound cannot be enjoyed. 
There are audio systems in which the left and right sound volumes and the 
delays can be automatically adjusted, but in a multi-channel system, an 
optimum listening cannot be obtained only by adjusting the sound balance. 
Particularly, recently, demands for high quality audio and A/V (home 
theater) systems are increasing. Further, in order to give a more real 
sensation, the sounds of movies and videos are supplied not only in the 
left and right form, but also in a front and rear form. Accordingly, the 
listening environments for the multi-channel audio systems are greatly 
diversified, and therefore, it is difficult to place the speakers at 
proper positions. Therefore it is impossible to obtain an ideal listening, 
and it aggravates economy to modify the listening room based on the audio 
system. 
SUMMARY OF THE INVENTION 
The present invention is intended to overcome the above described 
disadvantages of the conventional techniques. 
Therefore it is an object of the present invention to provide an apparatus 
for automatically equalizing a personal multi-channel audio system, and a 
method therefor, in which the multi-channel sounds are received as an 
input, and the listening environment is measured and the reproduction 
characteristics are corrected in accordance with the positions of the 
speakers and the characteristics of the listening environment, thereby 
reproducing the optimum sounds at the given environment. 
It is another object of the present invention to provide an apparatus for 
automatically equalizing a personal multi-channel audio system, and a 
method therefor, in which an effect of many speakers is obtained with a 
small number of speakers by phantom channels, and in the case of an A/V 
system, the sound reproduction range can be adjusted in accordance with 
the size and position of picture.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a block diagram showing the overall constitution of the apparatus 
for automatically adjusting a multi-channel audio system according to the 
present invention. 
Referring to FIG. 1, a transfer characteristic measuring section 10 
converts digital white noises to analogue signals to sequentially 
reproduce them through speakers 12, and collects signals of a microphone 
11 through a buffer 13. Under this condition, transfer signals 16 thus 
collected are transmitted to a transfer function calculating section 20 so 
that the transfer characteristics can be calculated. 
A white noise generating section 15 is connected to the speakers 12 only 
during the initializing period, and then, is connected to audio output 
signals after the completion of the initialization. For this purpose, a 
switching function 14 is required. The white noise of the respective 
speakers 12 are generated in the order of the frontal left side, the 
frontal right side, the central portion, the rear left side and the rear 
right side. Under this condition, the channel in which a speaker is not 
connected does not have to be measured by carrying out an inputting by the 
user connecting section 60 in advance. 
The transfer function calculating section 20 calculates the transfer 
characteristics between the respective speakers and the listening 
position, i.e., the frequency characteristics, the delay time, the 
distance and the directions by utilizing the white noise signals and the 
transfer signals which have been transmitted from the transfer 
characteristic measuring section 10. The calculation of the transfer 
characteristics includes the calculation of the reference positions of the 
respective speakers, and the calculation of inverse characteristics 
between the transfer characteristics of the real speakers. Through these 
calculations, the characteristics of the respective speakers at the 
listening position become same as the characteristics at the reference 
position. These calculated transfer characteristics are used in adjusting 
the filter coefficient of a reproduction characteristic correcting section 
30. The actual positions of the respective speakers are calculated based 
on the signal arrival time difference between the microphones. 
The reproduction characteristic correcting section 30 corrects the sound 
reproduction characteristics by forming filters in accordance with the 
reproduction characteristics which have been calculated by the transfer 
function calculating section 20. Thus the section 30 receives the general 
sounds, and the output which has passed through the filter is outputted 
through the speakers 12. Under this condition, the transfer 
characteristics at the listening position becomes same as the 
characteristics at the reference position. If the corrected 
characteristics do not meet the tolerance range, a remeasurement is 
carried out, or the remeasurement is repeated until a satisfactory result 
is obtained. 
Further, once set up, the filter coefficient is stored into a memory, so 
that it can be used next time. For this part, the greater the length of 
the filter coefficient, the better the result. 
A phantom channel synthesizing section 40 synthesizes the sounds outside 
the range of the outputs of the speakers which are connected to the audio 
system. It synthesizes inputted sounds into signals of arbitrary 
directions by utilizing an audio characteristic data base (DB) 50. The 
synthesized phantom channel is reproduced mainly by the speakers of the 
frontal channel. Even in the case where only two speakers of the frontal 
channel are connected, the signals of the upper rear channel are formed 
into a phantom channel in reproducing them, and thus, a desired 
3-dimensional sound can be obtained. 
The audio characteristic DB 50 is a space for storing the sound 
characteristics of the basic speaker layout. That is, it stores the 
characteristics of frontal left/right sides, the central portion, the rear 
left/right sides and the upper side. The stored characteristics are used 
when an inverse filter is formed by the transfer function calculating 
section 20, and when the phantom channels are synthesized by the phantom 
channel synthesizing section 40. 
The user interface section 60 decides whether an automatic adjustment for 
the audio system should be carried out or not. Further, the section 60 is 
used when the size of the video media is inputted. The user interface 
section 60 includes a plurality of switches which are capable of inputting 
a plurality of data, while the inputted data control the operations of the 
respective sections. Further, the user interface section 60 displays the 
current system status and other necessary information in such a manner 
that they could be easily recognized. 
The automatic adjusting apparatus for the high fidelity personal or home 
use audio system according to the present invention is constituted and 
operates in the following manner. 
The transfer characteristic measuring section 10 uses random noises or MLS 
(maximum length sequence) noises. It outputs noise signals and sound 
signals in a selective manner. That is, during the measurement of the 
initialization, noise signals are outputted, while after the 
initialization, sound signals are outputted. For this purpose, the section 
10 is provided with a switching function 14. This switching function 14 
can be constituted in the form of software (S/W). 
The signals thus outputted drive the speakers 12 through a sound output 
circuit. Then the signals are collected by a microphone array at the 
listening position. The microphone array is composed of two or more 
microphones which are disposed with a certain distance between them. 
The transfer function calculating section 20 includes a digital signals 
processor (DSP), and calculates the transfer function by utilizing the 
mutual relationship between the collected transfer signals and the white 
noise of the transfer characteristic measuring section 10. Further, the 
section 20 compares the delays of the microphones with each other so as to 
calculate the direction of the speakers. 
The calculated transfer function is converted into inverse characteristics, 
so that it would become a transfer function based on the reference speaker 
arrangement of the sound characteristic DB 50. Under this condition, the 
reference speaker arrangement is selected by the user, and generally, the 
reference speaker arrangement should be such that the distance between the 
speakers and the listening position should be 2.5 m. In the case of an A/V 
system, in accordance with the relationship between the speakers and the 
orientations which are calculated based on the size and position of the 
video media, the frontal speakers are corrected in view of the size and 
position of the video media, thereby adjusting the synchronization between 
audio signals and video signals. 
The reproduction characteristic correcting section 30 receives as the 
filter coefficient the inverse characteristics which have been calculated 
by the transfer function calculating section 20 by means of a variable 
coefficient filter bank. Inputted sound signals are made to pass through a 
filter before being outputted from the section 30. Generally, the 
reproduction characteristic correcting section 30 is composed of an FIR 
(finite impulse response) filter, and the length of the coefficient is 
arbitrarily determined. 
The phantom channel synthesizing section 40 generates speaker position 
signals for speakers which do not exist, by utilizing the frontal speakers 
of the speaker layout and based on the inputted sound signals. That is, 
there is utilized a principle that phantom sounds can be generated by 
utilizing an HRTF (head related transfer function) of two or more 
speakers. The phantom channels thus generated are combined with the 
frontal left and right channels of the inputted sound signals by an adder 
45 so as to be inputted into the reproduction characteristic correcting 
section 30. 
The sound characteristic DB 50 stores the characteristics such as the HRTF 
and the like which are needed in the transfer function calculating section 
20 and the phantom channel synthesizing section 40. The characteristics 
such as the HRTF and the like which are needed in the transfer function 
calculating section 20 and the phantom channel synthesizing section 40 are 
transfer characteristics of the reference listening position relative to 
the respective reference speaker positions. These characteristics are 
stored in a ROM (read only memory), and therefore, a replacement can be 
done if needed. The respective characteristics may be composed of the 
lengths of different coefficients, and they transfer the characteristics 
such as HRTF and the like which are required by the filter of the 
reproduction characteristic correcting section 30 and the filter of the 
phantom channel synthesizing section 40. 
The user interface section 60 includes the following functions. That is, 
the kind of the white noise is selected, and a decision is made as to 
whether an initialization is executed during the activation of the system. 
Further, a selection is made as to whether phantom channels are to be 
synthesized, and the channels to be synthesized are selected. Further, the 
channels to be measured are inputted (when there is no input, an automatic 
recognition is made as to the presence or absence of the transfer signals, 
and if needed, the distance and orientation of the real speakers can be 
inputted). Further, the size and position of the video media are inputted. 
For carrying out the above described functions, a plurality of switches 
are provided. Further, the user connecting section 60 includes a display 
part for displaying the current system status and for confirming the 
selected functions. This display part is composed of an LED (light 
emitting diode) or an LCD (liquid crystal display). 
FIG. 2 is a conceptional view showing the adjustment of the positions of 
the multi-channel speakers relative to a listener. That is, there are 
shown the positions of the multi-channel speakers which have certain 
angular positions relative to the listener. 
FIG. 3 is a conceptional view showing phantom channels of an audio system 
having a small number of channels. The listener feels sounds of a large 
number of speakers, while there are actually a small number of speakers. 
FIG. 4 is a conceptional view showing the adjustments of position and size 
of video media. As the size of the screen becomes smaller, the positions 
of the speakers are adjusted. 
FIG. 5 is a flow chart showing the automatic adjustment of the 
multi-channel audio system. 
Referring to FIG. 5, the automatic adjusting method according to the 
present invention will be described. 
First, the user connecting section 60 checks as to whether an 
initialization can be executed (S11). If it is found that an 
initialization cannot be carried out, a normal operation is carried out 
based on the existing reproduction characteristics (S19). On the other 
hand, if it is found that an initialization can be carried out, then white 
noises are generated, and the transfer signals are measured (S12). Based 
on this, the transfer function is calculated (S13). 
Based on the transfer function thus calculated and based on the reference 
characteristics, an inverse filter coefficient is calculated (S14). When 
the signals have passed through the inverse filter to be reproduced 
through the speaker, a judgment is made as to whether the transfer 
characteristics of the listening position come within the tolerance range 
(S16). If they do not come within the tolerance range, the measurements, 
calculations and evaluations are executed again. After executing certain 
rounds, the result showing the smallest errors are selected as the filter 
coefficient. The user connecting section checks as to whether the phantom 
channels need to be synthesized (S17). 
If the phantom channels need to be synthesized, the reference 
characteristics are applied in accordance with the kinds of the phantom 
channels. Further, the inputted sound signals are modified based on the 
reference characteristics, and the synthesized phantom channels are added 
to the frontal left and right channels (S18). Then multi-channel sounds 
are reproduced by means of the reproduction characteristic correcting 
filter based on the channels which are connected to the speakers (S19). 
According to the present invention as described above, various degrading 
factors due to the listening environments are automatically adjusted. That 
is, the listening environment characteristics are measured, and the 
reproduction characteristics of the audio system are corrected, so that 
sounds can be reproduced with the optimum condition at the given listening 
environment, and that 2 or 3 speakers can give an effect of 5 or 6 
speakers through the synthesis of phantom channels. In the case of an A/V 
system, the reproduction range is adjusted in accordance with the size of 
the screen, so that a more appealing A/V system can be realized. Thus with 
a given listening environment and with a given audio system, high quality 
sounds can be appraised, thereby meeting the desires of the general 
people.