Reflection sound compression apparatus

Abstract: A reflection sound compression apparatus extracts and compresses, most appropriately with a physical evaluation value, an impulse response of a hall, etc. which are obtained by calculation and actual experiment to reflection sounds in the number required by a sound field controller by using a learning identification method.

Description: 1. Field of the Invention The present invention relates to a reflection sound compression apparatus for installation in a sound field controller which allows an arbitrary sound field such as those in halls, etc. to be generated in a conventional room. 2. Prior Art With the development of a simulation technology for a hall using a computer and a trend toward a digital technology for acoustic devices today, a need for sound field control has been rapidly increasing. For this sound field control, a device for generating a sound field is used by performing convolution of a musical signal and an impulse response (reflection series) of hall, etc., called a sound field controller. Although the convolution performed in this sound field controller can be realized by a DSP (digital signal processor) or a discrete IC, there is a limitation in the length of impulse response (the number of reflections using which convolution is performed) due to performance of the existing DSPs and ICs, and thus the convolution is normally performed by adjusting (compressing ) the impulse responses measured in practice at the renown halls, etc. and also determined with calculations of simulation, etc. Explanation will follow below of an example of the conventional reflection compression apparatus which compresses the above-mentioned impulse response, with reference to drawings. Fig. 3 shows a block diagram of a conventional reflection compression apparatus. In Fig. 3, numeral 10 represents a memory circuit of RAM (Random Access Memory) which memorizes an impulse response of hall, etc. determined by measurement or calculation; 11 represents a calculating circuit which calculates an average energy of the reflection sounds in a time interval from the impulse response memorized in the memory circuit 10, and allocates the value at a position of the reflection sound at which the maximum value is obtainable within the time interval; 12 represents a setting circuit for setting the reflection sound determined by the circuit 11 on a sound field controller; 13 represents a sound field controller for producing a sound field by performing convolution of a musical signal and the reflection sound set by the setting circuit 12; 14 represents a group of speakers responsive to the output signal of the sound field controller 13; S M represents musical signals reproduced by compact disks, etc. Fig. 4 shows diagrams for exhibiting a method of calculation in the calculating circuit 11, in which (A) represents a schematic diagram of impulse responses obtained by measurement or calculation followed by digital sampling, (B) represents a reflection sound determined by the calculation circuit 11 exhibiting the magnitude of reflection sound at Ei (i equals to 1 - 8), and (C) represents a reflection sound compressed into the practically processable number (in this case 6 pieces) at the sound field controller. Also, T as shown in Fig. 4 (B) represents a time interval in which the reflection sounds are extracted. In the reflection sound compression apparatus structured as shown in Fig. 3, impulse responses as determined by the calculation for the simulation of impulse responses or sound ray method, etc. which were measured in the real halls, etc. are stored in the memory circuit. Then, the calculation circuit 11 calculates average energy of reflection sound in a certain time interval as shown in Fig. 4, allocates the value at the position of the reflection sound at which it takes the maximum value within the time interval, and makes other reflection sounds zero. The method of calculation is shown with a formula as follows; (N: Number of reflection sounds in a time interval) where E i is a magnitude of reflection sound extracted in the time interval of i as shown in fig. 4, h (n) is an impulse response stored in the memory circuit 10, and n is a parameter representing a time. The i as shown in the formula above is the number of reflection sounds which enable the convolution to be performed in the sound field controller 13. The calculation above corresponds to (A) and (B) in fig. 4, and is in reality compressed to the number of reflection sounds which make processing possible with the sound field controller. The method of this compression adopts, for instance, a way in which reflection sounds in the number possible to perform the convolution are taken in the order from a bigger sound from the reflection sounds compressed to (B) in Fig. 4. In this way, the reflection sounds determined by the calculation circuit 11 are set in the sound field controller 13 by the setting circuit 12, thereby allowing a greater number of reflection sounds determined by measurement and calculation to be compressed to the number of reflection sounds which are processable in reality. However, with such a conventional reflection sound compression apparatus, there is no means to appraise the physical approximation level between the original impulse response and the reflection sound as determined, and that there is such a problem as setting data in the sound field controller by extracting the data without objectivity to a high degree so that this approximation level finally needs correction by human psychological scale. A further sound field processing system is disclosed in EP-A-335468, wherein a matrix technique is used for generating sound fields in a plurality of speakers from signals generated in a plurality of microphones. This system is very different from that of the present invention in that signals from several microphones are processed rather than a single signal. The simplification techniques improved upon in the present invention are not applicable to a multiple signal system. SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection sound compression apparatus capable of most suitably extracting and compressing reflection sounds by a physical evaluation scale. In order to attain the above object a reflection sound compression apparatus of the present invention comprises: a reflection sound compression apparatus comprising: signal generating means for generating a random signal X(t), first memory means having stored therein a predetermined impulse response h(n), where 1 ≤ n ≤ N, N being a length of the impulse response; reflection sound extracting means for compressing and extracting a predetermined number of reflection sounds from the impulse response stored in the first memory means; second memory means for storing the reflection sounds extracted from the reflection sound extracting means; first calculation means for performing convolution of the impulse response stored in the first memory means and the random signal from the signal generating means to obtain a signal Y(n); second calculation means for performing convolution of the reflection sounds stored in the second memory means and the random signal from the signal generating means to obtain a signal Y'(n); third calculation means for calculating a difference e(n) between output signals from the first and second calculation means and employing said difference in correcting the reflection sounds such that said difference is decreased and then storing the corrected reflection sounds in the second memory means; and comparison means for analysing said difference e(n) calculated by the third calculation means, and, when the difference satisfies a predetermined condition, stopping the calculation of the third calculation means and setting the reflection sounds stored in the second memory means to a sound field controller for producing a sound field from the set reflection sounds and a music signal. With the configuration as mentioned above, the third calculation means consecutively corrects the reflection sounds stored in the second memory means by the learning identification method so that the difference between output signals from the first and second calculating means is made smaller. When the difference becomes within a predetermined condition, the correction of reflection sounds stored in the second memory means by the third calculating means is stopped and the corrected reflection sounds in the second memory means are set to the sound field controller by the comparison means. Accordingly, a limited number of reflection sounds can be most suitably extracted from a certain impulse response with a physical evaluation scale, thus making it possible to set objective data in the sound field controller. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a block diagram of a reflection sound compression apparatus in a first embodiment of the present invention, Fig. 2 shows a block diagram of a reflection sound compression apparatus in a second embodiment of the present invention, Fig. 3 shows a block diagram of a conventional reflection sound compression apparatus, and Fig. 4 shows a schematic diagram showing a conventional reflection sound extracting method. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a block diagram of a reflection sound compression apparatus in a first embodiment of the present invention. In Fig. 1, numeral 1 represents a signal generating circuit for generating a random signal such as white noise, etc.; 2 represents a first memory circuit which has stored therein an impulse response of such as a hall determined by measurement or calculation such as a computer simulation; 3 represents a first calculation circuit for performing convolution of an output signal from the signal generating circuit 1 and the impulse response stored in the first memory circuit 2; 4 represents a reflection sound extracting circuit which divides the impulse response stored in the first memory circuit 2 into a plurality of time blocks each being preferably 50 msec, extracts from reflection sounds in each time block a reflection sound having a maximum level (others being made zero) to obtain a series of reflection sounds, and extracts a required number of reflection sounds from the series of reflection sounds in the order from the largest level to the smaller (the remaining reflection sounds being made zero); 5 represents a second memory circuit for storing the reflection sounds extracted by the reflection sound extracting circuit 4: 6 represents a second calculation circuit for performing convolution of the output signal from the signal generating circuit 1 and the series of reflection sounds stored in the second memory circuit 5; 7 represents a third calculating circuit for correcting the series of reflected sounds stored in the second memory circuit 5 by a learning identification method using calculation results of the first and second calculation circuits 3 and 6; 8 represents a comparison circuit for analyzing a difference between the calculation results of the first and second calculation circuits 3 and 6, and, when the difference satisfies a predetermined condition, stopping the correction calculation of the third calculation circuit 7 and outputting the corrected reflection sounds stored in the second memory circuit 5; 9 represents a sound field controller for generating a sound field by performing convolution of the reflection sounds outputted from the comparison circuit 8 and a musical signal inputted from the outside; 9-1 represents plural speakers responsive to output signals from the sound field controller; and S represents a musical signal reproduced from a compact disk, etc. Each of the first memory circuit 2 and the second memory circuit 5 includes a RAM (Random Access Memory). The first calculation circuit 3, reflection sound extracting circuit 4, second calculation circuit 6, third calculation circuit 7 and comparison circuit 8 may be realized by a microcomputer. An impulse response of such as a hall, etc. determined by measurements or by the simulation of a sound ray method, etc. is stored in the first memory circuit 2. In the reflection sound extracting circuit 4, the impulse response stored in the first memory circuit 2 is read out and divided into a plurality of time blocks (each about 50 msec). Only maximum reflection sounds which are taken among reflection sounds in the respective time blocks are extracted. That is, in each divided time block, only a reflection sound which has the maximum level, is left by making the levels of other reflection sounds zero. This process is made for all divided time blocks, respectively. After performing the above process, reflection sounds inin the number required to be used in the sound field controller are extracted in the order of from the largest level reflection sound and the remaining reflection sounds are made zero. The series of extracted reflection sounds are stored in the second memory circuit 5. When this condition resulted, a random signal such as white noise, etc. is inputted from the signal generation circuit 1 to the first and second calculation circuits 3 and 6. In the first calculation circuit 3, convolution is performed for the random signal and the impulse response stored in the first memory circuit 2. When assuming a white noise to be X(n) (n: a parameter showing a sampling time for signal), an impulse response to be h (n) (a length to be N), calculating result to be Y (n), the convolution to be performed with the first calculation circuit is expressed in the following formula (All the functions below are dealt as a discrete sequence on a time domain). At the same time, in the second calculation circuit 6, a convolution is performed for the white noise and the reflection sounds stored in the second memory circuit 5. This is expressed as follows for calculation, by assuming the reflection sound stored in the second memory circuit 5 as h′ (n) and the calculation result as Y′ (n); In the first and second calculation circuits 3 and 6, the calculations as shown in formulae (2) and (3) are performed every time the signal is inputted from the signal generator 1 (every time n advances by one). In the third calculation circuit 7, correction is made for reflection sound h′ (n) stored in the second memory circuit 5 by a learning identification method using the calculation results Y (n) and Y′ (n) of the first and second calculation circuits 3 and 6. The correction of h′ (n) by the learning identification method is shown in the following formulae; h' (n) = h' (n) + Δh' (n) e (n) = Y (n) - Y' (n) α : Step size parameter ( 0 < α < 2 ) This correction is also performed each time X (n) is inputted in the same manner as the first and second calculation circuits. The reflection sound thus corrected is again stored in the second memory circuit 5. This correction is consecutively performed until a command to stop the correction comes from the following comparison circuit 8. The comparison circuit 8 inputs e(n) determined in the third calculation circuit 7, and calculates a root mean square by a certain number of this values. (Experimentally, this number of values depends on h (n), but about 100 is appropriate for N of about 640.) When this mean value converges on a certain value or becomes less than a certain value (It is experimentally confirmed that it is sure to converge on a certain value.), a command is issued to stop calculation of the third calculation circuit 7 and the corrected reflection sounds which are stored in the second memory circuit 5 are sent to the sound field controller 9. The process described above allows the impulse response determined by measurement or calculation to be compressed to the number of reflection sounds necessary for the sound field controller. In the third calculation circuit in the embodiment, a learning identification method is used, but another correction method which makes the difference minimum may be used. Fig. 2 shows a block diagram of a reflection sound compression apparatus in a second embodiment of the present invention. In Fig. 2, numeral 4-1 is a reflection sound extracting circuit for reading out the impulse response stored in the first memory circuit 2, integrating the absolute values of certain reflection sounds in each divided time block (experimentally, about 50 msec is preferable), setting the mean value of the absolute values to a position of a reflection sound which has the maximum level in the time block while making other reflection sounds zero to obtain a series of reflection sounds, and for extracting from the series of reflection sounds the necessary number of reflection sounds in the order from the largest value to the smaller while making the remaining reflection sounds zero. In the figure, elements which have the same functions as those in Fig. 1 are shown with the same numerals. Since only the action of the reflection sound extracting circuit 4-1 is different from the first embodiment, its action alone is explained. In the reflection sound extracting circuit 4-1, the impulse response stored in the first memory circuit 2 is read out and divided into a plurality of time blocks (each being about 50 msec). Absolute values of reflection sounds in each time block are integrated, and the integration result is divided by the number of reflection sounds in the time block to thereby obtain a mean value in the time block. This mean value is set to a time position at which the maximum value of reflection sound level in the time block exists, while making other reflection sound levels in the time block zero. Then, the number of reflection sounds to be used in the sound field controller are extracted from the thus obtained series of mean values in the order from the largest value and making the remaining reflection sounds zero. The extracted series of reflection sounds are stored in the second memory circuit 5. The reflection sounds extracted by the reflection sound extracting circuit 4-1 are the same as those shown in Fig. 4. Other actions are the same as those in the first embodiment.

Claims: A reflection sound compression apparatus comprising: signal generating means (1) for generating a random signal X(t), first memory means (2) having stored therein a predetermined impulse response h(n), where 1 ≤ n ≤ N, N being a length of the impulse response; reflection sound extracting means (4) for compressing and extracting a predetermined number of reflection sounds from the impulse response stored in the first memory means (2); second memory means (5) for storing the reflection sounds extracted from the reflection sound extracting means; first calculation means (3) for performing convolution of the impulse response stored in the first memory means and the random signal from the signal generating means to obtain a signal Y(n); second calculation means (6) for performing convolution of the reflection sounds stored in the second memory means (5) and the random signal from the signal generating means (1) to obtain a signal Y'(n); third calculation means (7) for calculating a difference e(n) between output signals from the first and second calculation means and employing said difference in correcting the reflection sounds such that said difference is decreased and then storing the corrected reflection sounds in the second memory means (5); and comparison means (8) for analysing said difference e(n) calculated by the third calculation means (7), and, when the difference satisfies a predetermined condition, stopping the calculation of the third calculation means (7) and setting the reflection sounds stored in the second memory means (5) to a sound field controller (9) for producing a sound field from the set reflection sounds and a music signal. An apparatus as set forth in claim 1, wherein the reflection sound extracting means (4) divides the impulse response stored in the first memory means (2) into a Plurality of time blocks, extracts only a reflection sound which takes a maximum level from reflection sounds in each time block while making zero other reflection sounds in the each time block to obtain a series of extracted reflection sounds, and extracts from the series of extracted reflection sounds the predetermined number of reflection sounds in the order from the largest level to the smaller while making zero the remaining reflection sounds. An apparatus as set forth in claim 1, wherein the reflection sound extracting means (4) divides the impulse response stored in the first memory means (2) into a plurality of time blocks, replaces a reflection sound having a maximum level in each time block by a reflection sound having a mean value of levels of reflection sounds in the each time block while making zero other reflection sounds in the each time block thereby to obtain a series of extracted reflection sounds, and extracts from the series of extracted reflection sounds the predetermined number of reflection sounds in the order from the largest level to the smaller while making zero the remaining reflection sounds. An apparatus as set forth in claim 1, wherein the comparison means (8)calculates a mean value of the square of the difference between the output signals from the first and second calculation means, (3,6) and, when the mean value becomes equal to a predetermined value, stops the calculation of the third calculation means (7) and sets the reflection sounds stored in the second memory means (5) to the sound field controller (9).

Inventors: KAWAMURA AKIHISA, MATSUMOTO MASAHARU, NUMAZU HIROKO, SATO KATSUAKI, SERIKAWA MITSUHIKO, KAWAMURA, AKIHISA, MATSUMOTO, MASAHARU, NUMAZU, HIROKO, SATO, KATSUAKI, SERIKAWA, MITSUHIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G10K15
IPC codes: G10K15, H03G5, E04B1