JPH08247837A - Reverberation time automatic measuring method and reverberation time automatic measuring device - Google Patents

Abstract

PURPOSE: To provide a reverberation time automatic measuring method and a reverberation time automatic measuring device which can measure the reverberation time automatically at a high efficiency and a high accuracy. CONSTITUTION: In a time mean S/N calculator 7, a time mean S/N in an impulse response is found. In an 0dB detector and an observation section deciding member 11, the time zone that the time mean S/N is made to the time of the first 0dB from the direct sound reaching time in the impulse response is detected to decide the observation section. In an inclination calculator 12, the inclination of the minimum square approximate line of an acoustic energy decay curve in the decided observation section is calculated, and in a reverberation time calculator 13, the reverberation time is calculated from the found inclination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverberation time automatic measuring method and a reverberation time automatic measuring apparatus capable of accurately estimating the slope of an acoustic energy attenuation curve representing a room acoustic characteristic.

SUMMARY OF THE INVENTION The present invention provides a sufficient signal-to-noise in a low frequency band when obtaining an acoustic energy attenuation curve necessary for calculating a reverberation time from an impulse response representing an acoustic transfer characteristic in a room. Even if the ratio (hereinafter referred to as S / N) cannot be obtained, the process of estimating the slope of the attenuation of acoustic energy by adopting the portion before the acoustic energy attenuation is affected by noise as the observation section It relates to a method of automatically performing. Until now, when obtaining the reverberation time from the impulse response, the S / N evaluated at the measurement site is often sufficient even in the middle and high frequencies, but is often not sufficient especially in the low frequency band. In some cases, an accurate reverberation time could not be obtained because the attenuation curve was bent due to the influence of noise and separated from the original attenuation. On the other hand, an improvement measure has been proposed in which the signal component is extracted by obtaining the root mean square value of the noise from the no-signal portion of the obtained impulse response and subtracting it, but the S / N is not sufficiently improved. Therefore, it was necessary to visually check the portion of the obtained attenuation curve where the influence of noise was small, and recalculate the reverberation time. In the present invention, the effect of noise on the signal is monitored by observing the S / N (time average S / N) every moment after the direct sound arrival time, and the time average S / N is 0 dB or more. The part where the influence of noise is small is taken as the observation section, and the slope of the energy attenuation curve is estimated by performing the least squares approximation of that part, and the reverberation time with high accuracy can be efficiently obtained.

[0003]

2. Description of the Related Art Conventionally, an acoustic energy decay curve has been obtained from an impulse response representing a room acoustic transfer characteristic, and a reverberation time has been calculated based on the acoustic energy decay curve.

However, when the reverberation time is calculated from the impulse response, the S / N evaluated at the measurement site is often sufficient even in the middle and high frequencies, but is often insufficient especially in the low frequency band. In such a case, there is a case where the attenuation curve is bent due to the influence of noise and is separated from the original attenuation, and an accurate reverberation time cannot be obtained.

It has been argued so far that the observation section of the attenuation curve becomes a problem when obtaining the reverberation time from the acoustic energy attenuation curve with an insufficient S / N, and the root mean square value of the noise energy is not calculated. S / N calculated from the signal part and subtracted from the obtained acoustic energy attenuation curve
There is a report that an accurate reverberation time can be calculated by improving the above (WT Chu, JASAS Vol. 6).
3, No. 5 1444-1459 (1978)).

However, since the S / N is not sufficiently improved even by the above-mentioned improvement measure, it is said that human beings visually confirm the portion of the obtained attenuation curve where the influence of noise is small, and re-calculate the reverberation time. Work was needed.

[0007]

As described above, the acoustic energy decay curve obtained from the impulse response is
In many cases, the S / N is not sufficient in a low frequency band, etc., and the acoustic energy attenuation curve is bent due to the influence of noise and deviates from the original attenuation, so it is necessary to obtain an accurate reverberation time. A problem is how to evaluate an appropriate portion that is not affected by noise from the obtained acoustic energy attenuation curve, and it is desired to develop a method that quantitatively evaluates the optimum observation section and automatically determines it.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an automatic reverberation time measuring method and an automatic reverberation time measuring device capable of automatically measuring reverberation time with high efficiency and high accuracy. It is in.

[0009]

In order to achieve the above object, the invention according to claim 1 is to calculate the reverberation time by obtaining an acoustic energy attenuation curve from an impulse response in acoustic measurement of a space to be measured. The reverberation time is calculated from the slope of the least square approximation line of the acoustic energy attenuation curve in the time zone from the arrival time of the direct sound in the impulse response to the time when the momentary S / N (time average S / N) first becomes 0 dB. The feature is that it is calculated.

The invention according to claim 2 is a device for calculating a reverberation time by obtaining an acoustic energy decay curve from an impulse response in a space to be measured, and means for obtaining a time average S / N in the impulse response. , Means for detecting the time zone from the time when the direct sound arrives in the impulse response to the time when the time average S / N first becomes 0 dB, and the slope of the least square approximation line of the acoustic energy decay curve in the detected time zone. It is characterized in that it is provided with a means for calculating and a means for calculating the reverberation time from the obtained inclination.

[0011]

According to the present invention having the above-described structure, the S / N (time average S) is calculated every moment from the time when the direct sound arrives in the impulse response.
/ N) to monitor the effect of noise on the acoustic energy decay curve of the signal component. Then, the time zone from the direct sound arrival time in the impulse response to the time when the time average S / N first becomes 0 dB is detected. Since this time zone is the part where the influence of noise is small, it is set as the observation section, and the slope of the least-squares approximation line of the acoustic energy attenuation curve in this observation section (time zone) is calculated (estimated), and the reverberation time is calculated from the obtained slope. Is calculated.

[0012]

1 is a block diagram showing the configuration of an embodiment of an automatic reverberation time measuring apparatus according to the present invention, and FIG. 2 is an explanatory view showing a measurement environment of a space measured by the automatic reverberation time measuring apparatus.

The automatic reverberation time measuring apparatus 1 includes a noise part detecting section 2, a noise level calculating section 3, an input signal level calculating section 4, a subtracting section 5, a dividing section 6, and a time average S / N calculating section. 7, 0 dB detection unit 8, noise removal unit 9, attenuation curve calculation unit 10, observation section determination unit (gate unit) 11
And a slope calculation unit 12 and a reverberation time calculation unit 13,
As shown in FIG. 2, the impulse response of the measurement target space 30 is input and its reverberation time is automatically measured. In the measurement target space 30, as shown in FIG. 2, the impulse response measurement signal generator 20 is installed. The impulse response measurement signal generated from the device 20 is a speaker SP.
Is output to the measurement object space 30 via the, and the direct sound wave and the reflected sound wave are picked up by the microphone MC, and
It is adapted to be supplied to the reverberation time measuring device 1 via the filter section 40.

The noise portion detecting section 2 detects a non-signal portion in the input impulse response as a noise portion. Specifically, a delay time from the input of a capture start signal output at the same time as the signal generation from the impulse response measurement signal generator 20 and the direct sound arrival at the sound receiving point microphone MC Let the part be a non-signal part.

The noise level calculation unit 3 detects the noise level by calculating the root mean square of the detected noise portion.

The input signal level calculation unit 4 obtains the root mean square value of the input signal at each short time of several tens of millimeters to several milliseconds (for example, 16 ms) in the signal portion of the input impulse response to obtain the input signal level. To detect.

The subtracting section 5 subtracts the noise level detected by the noise level calculating section 3 from the input signal level detected by the input signal level calculating section 4, and the dividing section 6 outputs the subtraction output of the subtracting section 5. And the noise level detected by the noise level calculation unit 3 are obtained, and the ratio is supplied to the time average S / N calculation unit 7.

The time average S / N calculator 7 continuously obtains the ratio data supplied every ten to several milliseconds to several milliseconds (for example, 16 ms) until the input signal is sufficiently attenuated from the direct sound arrival, and the time average is obtained. Calculate the S / N curve.

The 0 dB detecting section 8 obtains the time when the time average S / N calculated by the time average S / N calculating section 7 becomes 0 dB, and supplies it to the observation section determining section 11.

On the other hand, the noise removing unit 9 detects the non-signal portion from the input impulse response, removes it as noise, and supplies the signal from which noise has been removed to the attenuation curve calculating unit 10.

The attenuation curve calculation unit 10 executes an operation of obtaining an attenuation curve of acoustic energy from a signal obtained by removing noise from an input signal.

The observation section determining section (gate section) 11 is a section for determining the observation section of the obtained attenuation curve, and is 0d.
Processing for cutting out the attenuation curve output from the attenuation curve calculation unit 10 by the gate signal output from the B detection unit 8 whose observation section is the time from the arrival time of the direct sound until the time average S / N first becomes 0 dB do.

The slope calculating unit 12 obtains the slope of the least squares approximation line in the attenuation curve cut out by the observation section determining unit 11.

The reverberation time calculation unit 13 executes a process for obtaining the reverberation time from the inclination calculated by the inclination calculation unit 12.

Next, the reverberation time measuring process in this embodiment will be systematically described with reference to the functional block diagram of FIG. 1 and the flowchart of FIG.

Further, FIG. 4 shows an example of an observed waveform used in this embodiment.

<Noise Level Detection Processing (Step ST
1)> First, the non-signal portion in the impulse response input by the noise portion detection unit 2 is detected as a noise portion, and the noise level calculation unit 3 obtains the energy root mean square value of the noise from the non-signal portion, and the noise level Is calculated. The non-signal part can be created by taking a long time during measurement. For example, if the acquisition is started at the same time as the acquisition start signal supplied from the impulse response measurement signal generator 20 as described above, the delay time until the direct sound arrives at the microphone MC of the reception sound becomes a no-signal portion. .

<Signal level detection processing (step ST2)
> In the input signal level calculation unit 4, the input impulse response is in the range of ten to several milliseconds (for example, 16 m).
The root mean square value of the input signal is obtained every short time (s).

<Time average S / N calculation process (step ST
3)> The ratio of the root mean square value of the input signal and the noise obtained by the above process is obtained every several milliseconds to ten and several milliseconds, and this is from the arrival of the direct sound until the input signal is sufficiently attenuated.
The time average S / N curve is obtained repeatedly and is obtained (processing of the time average S / N calculation unit 7). This time average S /
N can be calculated by the following equation. The time average S / N curve thus obtained is shown in FIG.

[0030]

[Equation 1] <Noise removal process (step ST4)> In parallel with the above process, noise removal is performed by the conventional method in the noise removal unit 9 from the noise part cut out by the noise part detection unit 2 and the obtained impulse response. It

<Attenuation curve calculation process (step ST5)>
When the noise is removed, the attenuation curve calculation unit 10 performs an operation of obtaining an attenuation curve for the signal.

FIG. 5 shows the attenuation curve thus obtained.

<Observation section determination process (step ST6)>
In the observation section determination unit 11, when the time average S / N first becomes 0 dB from the 0 dB detection unit 8, the observation section determination unit 11 uses a gate signal whose observation section is the time from the direct sound arrival time to 0 dB. A process of cutting out the attenuation curve output from the attenuation curve calculation unit 10 is performed.

<Slope calculation process (step ST7)> The slope of the least-squares approximation line is obtained for the attenuation curve in the obtained observation section.

<Reverberation time calculation process (step ST8)>
The reverberation time is calculated based on the calculated slope. The reverberation time thus obtained is output as a result.

Next, the function and effect of the above processing will be described.

In the attenuation curve obtained by the attenuation curve calculation processing shown in FIG. 5, curve A is a raw data curve when no processing is performed, whereas curve B is noise removal by a conventional method. It shows the attenuation in the case. Further, FIG. 6 shows a time average S / N curve, and the time average S / N first reaches 0 dB (in this embodiment, about 0.35 seconds), that is, 0 to 0. The attenuation curve estimated for 35 seconds as the observation section is the straight line C in FIG. The curve D shows the decay of the reverberation time (1 second) preset for reference, but it can be seen that the straight line C is very close to the curve D.

Table 1 shows the calculated reverberation time.
As can be seen from this table, the error from the set value (1 second) is within the human detection limit of 5%.

[0039]

[Table 1] As described above, according to the present embodiment, it is possible to automatically determine the observation section of the attenuation curve with high accuracy, and it is possible to efficiently measure the reverberation time. In addition, the measurement target space 30
In the case where the original attenuation curve itself of B is bent, if a person visually makes a conventional judgment, there is a possibility that it may be erroneously judged as a bending due to noise. However, in this embodiment, by always checking the time average S / N, Whether or not the influence of noise can be automatically judged accurately, and the observation section of the attenuation curve can be evaluated correctly.

[0040]

As described above, according to the inventions described in the claims, in calculating the reverberation time by obtaining the acoustic energy decay curve from the impulse response, the S that is momentary from the direct sound arrival time in the impulse response is calculated. / N (time average S / N) first calculates the reverberation time from the slope of the least-squares approximation line of the acoustic energy attenuation curve in the time zone until the time when it reaches 0 dB, so that the influence of noise can be considered. Therefore, the reverberation time can be automatically measured with high efficiency and high accuracy without human intervention.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic reverberation time measuring apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a measurement environment to which the reverberation time automatic measurement device according to the present invention is applied.

FIG. 3 is a flowchart showing a processing procedure in an embodiment of the present invention.

FIG. 4 is a waveform chart showing an example of an observed waveform used in one embodiment of the present invention.

FIG. 5 is a waveform diagram showing an example of an attenuation curve in an example of the present invention.

FIG. 6 is a waveform diagram showing an example of a time average S / N curve in an example of the present invention.

[Explanation of symbols]

 1 Automatic Reverberation Time Measuring Device 2 Noise Part Detecting Part 3 Noise Level Calculating Part 4 Input Signal Level Calculating Part 5 Subtracting Part 6 Dividing Part 7 Time Average S / N Calculating Part 8 0 dB Detecting Part 8 9 Noise Removing Part 10 Attenuation Curve Calculating Part 10 11 Observation section determination unit 12 Slope calculation unit 13 Reverberation time calculation unit 20 Impulse response measurement signal generator 30 Measurement target space

Claims (2)

[Claims] 1. In acoustic measurement of a space to be measured, when calculating a reverberation time by obtaining an acoustic energy decay curve from an impulse response, an S / N (time average S / N) from the arrival time of a direct sound in the impulse response is calculated. N)
The reverberation time automatic measuring method is characterized in that the reverberation time is calculated from the slope of the least-squares approximation line of the acoustic energy attenuation curve in the time zone up to the time when is first 0 dB. 2. An apparatus for obtaining a reverberation time by obtaining an acoustic energy decay curve from an impulse response in a space to be measured, a means for obtaining a time average S / N in the impulse response, and a direct sound arrival time in the impulse response. To means for detecting the time zone from the time when the time average S / N first becomes 0 dB, and means for calculating the slope of the least-squares approximation line of the acoustic energy attenuation curve in the detected time zone. An apparatus for automatically measuring reverberation time, comprising: means for calculating reverberation time from the slope.