JPH0135288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring transient characteristics, particularly reverberation characteristics, of a transmission system.

In general, it is often necessary to carry out targeted characteristic measurements in order to learn various characteristics of a particular acoustic room from an acoustic point of view. For example, when a lecture is given in a single hall or a musical performance is performed by a band, the acoustic effects of the speech or music become important. In this case, if the attenuation characteristics for the signal from one signal source or the reverberation time are clearly understood, the structure of the venue where the event will be held and the acoustic characteristics This means that you can aim for high acoustic effects.

Among various acoustic characteristics, several methods have been considered in the past for measuring transient characteristics such as reverberation time characteristics, for example, attenuation characteristics.

One method is to measure the attenuation characteristics of a sound receiving point when stationary band noise is cut off, for example. To minimize the effect of decay curve variations on such measured reverberation time values, it is necessary to repeat and average the reverberation measurements many times. However, this method is not only inefficient, but also does not reveal the true characteristics of the attenuation.

By the way, as a method to measure transient characteristics,
MR Schroeder's so-called impulse response square integration method is known. The principle is that when the sound source band noise is cut off from the steady state, the transient characteristics of the sound receiving point, for example, the essential transient characteristics <S ² (t)> corresponding to the average of ∞ times of the reverberation decay curve, are calculated from the sound source.・
The sound pressure level S(t) at a certain point in time t of the transient characteristic is expressed as follows.

<S ² (t)>=N∫ ^∞ _t r ² (x) dx ………(1) However, N: Power of sound source band noise, r(x): Impulse response Therefore, the integral section [t, + ∞] and integrate the squared impulse response r(x), an infinite set average of the squares of the sound pressure level S(t) at time t can be obtained. Based on the above principle, methods for obtaining the transient characteristics of a chamber, such as a reverberation curve, can be roughly divided into the following two methods. (1) is the so-called double impulse method, and (2) is the so-called backward integration method.

The principle of the double impulse method (1) is carried out by expanding the principle equation (1) above as follows.

<S ² (t)>=N∫ ^∞ _t r ² (x) dx = N∫ ^∞ ₀ r ² (x) dx−N∫ ^t ₀ r ² (x) dx ...(2) Here, the integral interval [ 0, +∞], and then calculate the integral interval [0, +∞] that changes from time to time.
t] by sequentially subtracting the square integral of the impulse response r(x), the transient characteristic < S ² (t)
> is required.

FIG. 1 shows the configuration of a conventional device for measuring reverberation characteristics according to this principle.

In this figure, an impulse signal from an impulse source 2 (e.g. a paper pistol) is
Pick up the second impulse with microphone 3,
After the output is sent to the squaring circuit 4 and squared, it is sent to the integrating circuit 6 via the switch SW, where the signal is integrated and displayed on the display device 7. When generating the second impulse, change the switch SW to connect it to the inverting circuit 5 to invert it, and then connect it to the inverting circuit 6.
If the output is displayed through the , a transient characteristic such as a reverberation curve can be obtained as a process of subtracting the latter from the former.

However, with this double impulse method, it is technically almost impossible to accurately generate two identical pulses as a sound source, that is, to reproduce the second impulse exactly the same as the first. Therefore, since the shapes of the generated impulses are different, there is a drawback that the measurement error becomes large especially at the end of the integration, that is, at the end of the reverberation curve where the level is small.

_In addition, the principle of ^the backward integration method in ( ² ) is to convert _the principle formula ⁱⁿ (1 ^{) into} -x) dx ......The method used is to integrate in the opposite direction as shown in (3). In other words, the integral interval [t, ∞] is changed to [-
∞, -t] to obtain the transient characteristic <S ² (t)>.

FIG. 2 shows the configuration of a conventional device for implementing this method.

In this figure, first, the impulse response r(x) from the picked-up microphone is once recorded on a tape recorder 4', and then the tape recorder 4' is reversed to reproduce the impulse response in reverse, and the output is The signal is supplied to a display device 7' via a squaring circuit 5' and an integrating circuit 6'. However, this method has the disadvantage that real-time processing cannot be performed because the collected impulse response is once recorded on a tape recorder. Therefore, it lacks immediacy.

In view of the above, the present invention provides a method and apparatus that can measure transient characteristics, such as reverberation characteristics, with high precision in real time using one impulse, such as a tone burst wave, without repeating reverberation measurements. It is. Further, an object of the present invention is to provide a method for measuring transient characteristics of a transmission system and an apparatus thereof filed by the same applicant, in which <S ² (t) ＞=∫ ^T ₀ r ² (x)dx−∫ ^T ₀ r ²
(x) A method and device for measuring the transient characteristics of a transmission system that further improves the accuracy around t→T associated with the calculation of dx and enables reproducible display of <S ² (t)> It provides: Another _object of the present invention is to detect ∫ ^ti ₀ r ² (x) dx (where i=1, 2, 3...
By storing n) in a storage device at a clock rate f _L lower than the basic clock rate f _s , the capacity of the storage device can be significantly reduced. It is about promoting. That is, the method according to the present invention provides an impulse response r
In the method of measuring the transient characteristics of a transmission system by analyzing (x), the impulse response r(x) is converted into a digital signal based on the basic cloak rate f _s from the sound source, and then the signal is squared and its The results are divided into many different integral intervals [0, ti (i=1,
2, 3...)], the integral of ∫ ^ti ₀ r ² (x)dx is digitally repeated and accumulated, and the accumulation result obtained in this way is ∫ ^ti(i=1 , ² ... ^T) ₀ r ² (x) dx is a clock rate f _L lower than the basic clock rate f _s (= f _s ×
2 ^-k ; k is a positive integer), and the transient response characteristic S ² (t)∫ ^T ₀ r ² (x) dx at the final integration time T is stored in the second storage means. Then, the stored contents of both are sequentially read out and the former is subtracted from the latter, that is, <S ²
(t)＞=∫ ^T _ti r ² (x)dx=∫ ^T ₀ r ² (x)dx−∫ ^ti ₀ r ²
(x)
It is characterized by calculating dx and displaying/recording the transient characteristics of the transmission system based on the results.

Further, the device according to the present invention is a device that analyzes the impulse response r(x) to measure the transient _{characteristics} of a transmission system. an analog/digital converter (abbreviated as A/D converter) for converting into
A circuit that calculates r ² (x) by squaring the conversion output from the conversion device, and a square output r ₂ (x) from the circuit.
an accumulator that calculates ∫ ^ti(i=1,2,3 … ^T) ₀ r ² (x) _dx based on A first storage device that stores data at a timing based on f _L (=f _s ×2 ^-k ) and a transient characteristic at the final integration time S ² (t) = ∫ ^T ₀ r ² (x)
A second storage device temporarily stores dx, and the contents stored in the first storage device and second storage device are read out and sequentially <S ² (x)>=∫ ^T ₀ r ² (x )dx
-∫ ^ti ₀ r ² (x) dx = ∫ ^T _ti r ² It consists of a subtraction device that calculates (x) dx, and a device that displays/records the transient characteristics of the transmission system based on the output from the subtraction device. It is characterized by

Next, an embodiment of an apparatus for determining the transient characteristics of a transmission system according to the present invention will be described with reference to the drawings.

FIG. 3 shows the configuration of an embodiment of the apparatus of the present invention. A chamber 11 is a room in which transient characteristics, such as reverberation characteristics, are to be measured, and a sound source 12 that generates an impulse is placed therein. This impulse source may be, for example, a paper pistol. First, a sound wave is collected using, for example, the microphone 13 in order to measure the impulse response r(x) from the sound source 12.
The impulses received in this way are transmitted to amplifier 1.
After being amplified in step 4, the analog signal is converted into a digital signal in an A/D converter 15. Note that FIG. 4a shows the output of the amplifier 14. The impulse response r(x) thus converted into a digital signal is squared by a squaring circuit 16 and sent to an accumulator 17 as an accumulator. In the accumulator 17 here, different integral intervals [o, ti
(i = 0, 1, 2, 3...T)] by repeatedly accumulating the integral ∫ ^ti _p r ² (x) dx and storing the result in a random access storage device ( RAM) 18. In this case, the A/D converter 15, the squaring circuit 16 and the accumulator 1
7 operate at a basic clock rate f _s (relatively high frequency) as shown in FIG. 3, and the storage device 18 operates at a clock rate f _L (=f _{s ×} 2 ^{- The} read timing is controlled by In addition, the integral value ∫ ^ti _p r ² (x) dx [where ti=0, 1, 2...t] of the digital signal stored in the storage device 18 is adjusted to a desired roughness according to the precision to be displayed. Just remember it. Therefore, if you want to display measured data in detail on the display device, set the clock rate f _L high to shorten the reading interval, and if you want to display it somewhat coarsely, set the clock rate f _L low. The data may be stored in the storage device 18 by increasing the reading interval. That is, A/
The number of storage elements in the storage device can be significantly reduced compared to the case where the entire D-converted impulse response r(x) itself is stored. Experiments have shown that 32 to 256 elements per display are usually sufficient for this purpose. Note that FIG. 4b shows the stored contents as analog quantities.

On the other hand, among the outputs from the accumulator 17, the integrated value at the final integration time T, that is, ∫ ^T ₀ r ² (x)dx is stored in the register 19 as a second storage device. In this way, storage device 1
8 and the contents stored in the register 19 are sequentially read out by the read pulse and sent to the subtraction device 20. This subtraction device 20 subtracts the content stored in the storage device 18 from the content stored in the register 19. That is, ∫ ^T _ti r ² (x)dx=∫ ^T ₀ r ² (x)dx −∫ ^ti ₀ r ² (x)dx is calculated. This calculation result is given to a logarithmic compressor (LOG) 21 such as a table using a read-only storage device (ROM), where it is logarithmically compressed and displayed on the display device 23 via the next stage interface circuit 22. Measured values are displayed one after another.
It is also possible to display and record the measured values. Note that FIG. 4c shows the above subtraction result as an analog quantity, and FIG. 4d shows a display signal.

In this way, the display (recording) device 23 has
Immediately after the impulse response received by the microphone 13 is digitally converted and the final integration is performed, the transient characteristics of the measured pulse are displayed in near real time.

As described above, in this invention, the impulse response r(x) is converted into a digital quantity,
Through digital arithmetic processing, a reverberation curve (transient response curve) can be obtained from a single impulse response r(x) with sufficient real-time performance for practical use, and the accuracy around the final point T can be obtained. In addition to being significantly improved, data can be stored in the storage device using coarse sampling according to the required display accuracy, making the configuration simpler and easier to use than an analog calculation processing method using an analog storage device. It is possible to realize a device at a relatively low cost.

In addition, in this type of measuring device that uses an analog storage device, the analog storage device itself does not have sufficient memory function and is not satisfactory in terms of accuracy. However, in this invention, the accuracy can be improved by digital processing. Improved transient characteristics of transmission systems can be measured.

[Brief explanation of drawings]

FIG. 1 shows a diagram explaining the double impulse method according to the prior art and its waveform, FIG. 2 shows a diagram explaining the backward integral method according to the prior art and its waveform, and FIG. 3 shows the transmission system according to the present invention. The configuration of an embodiment of the device for measuring the transient characteristics of
The figure shows signal waveforms illustrating the operation of the apparatus of the embodiment shown in FIG. 1...Chamber, 12...Sound source, 13...Microphone, 14...Amplifier, 15...A/D
Converter, 16... Square circuit, 17... Accumulator, 18... First storage device (RAM), 19... Second storage device (register), 20... Subtraction device, 21...ROM, 22
...interface circuit, 23...display device.

Claims (1)

[Claims] 1. A method for measuring transient characteristics of a transmission system by analyzing impulse response r(x), which includes a large number of integral intervals (0, ti (i=1, 2, 3,...n)). is set in advance, and the impulse response r(x) from the sound source is calculated based on the basic clock rate _fs.
is converted from an analog signal to a digital signal, the impulse response r(x) is digitally squared, and the square value of the impulse response r ² (x) is obtained.
Digitally iterate and accumulate ∫ ^ti ₀ r ² (x)dx
_{The clock rate f L (} =f _s ×
2 ^-k ; k is a positive integer), the digital values that are the calculation results are sequentially stored in the storage means 1, while the digital values that are the calculation results at the final point ∫ ^T ₀ r ² ( x) storing dx in a second storage means;
From the contents stored in the second storage means, the first
The contents stored in the storage means are sequentially subtracted, and the transient characteristics of the transmission system are displayed according to the subtraction output.
A method for measuring transient characteristics of a transmission system, characterized in that the transient characteristics of a transmission system are recorded. 2. In a device that analyzes the impulse response r(x) and measures the transient _{characteristics} of a transmission system, an analog/ a digital conversion device, a device operating on the basis of the basic clock rate f _s and digitally squaring the output from the conversion device, and an output of the device operating on the basis of the basic clock rate f _s and squaring the output; is cumulatively repeated to obtain a large number of different integral intervals (0, ti (i=1, 2,
an accumulator that digitally integrates with 3,...n));
a first storage device that samples and stores the integral output from the accumulator based on the basic clock rate f _L (=f _s ×2 ^-k ) _; a second storage device that temporarily stores the integral value ∫ ^T ₀ r ² (x)dx at the final integration time T out of the output from the accumulator; By sequentially subtracting the contents of the storage device, <S ² (t)>=∫ ^T ₀ r ² (x)dx−∫ ^ti ₀ r
²
(x) dx=∫ ^T _ti r ² (x) a subtraction device for calculating dx;
1. A device for measuring transient characteristics of a transmission system, comprising: a device for displaying/recording the transient characteristics of the transmission system based on the output from the subtraction device.