JPH0580161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pseudo pink noise generator suitable for sound field measurement.

(Prior Art) As one method of measuring acoustic characteristics such as reflection and reverberation of an acoustic space, as shown in FIG.
The pink noise generated by the speaker 2 is picked up by the microphone 3 and converted into an electrical signal, and this electrical signal is passed through a bandpass filter 4 having a 1/3 octave passband width and visualized on the display unit 5. things are being done. Note that pink noise has a continuous spectrum and
Noise that has constant energy per octave within a predetermined frequency range regardless of frequency position. That is, if energy characteristics are expressed by taking energy on the vertical axis and frequency on a logarithmic scale on the horizontal axis, the characteristics will be flat.

As another measurement method, as shown in FIG. 4, a wobble tone generator 6 whose frequency vibrates in a 1/3 octave width, for example, is used as a sound source to drive the speaker 2. The generated warble tone is also picked up by a microphone 3, converted into an electrical signal, and this electrical signal is directly added to the display section 5 for visualization.

(Problem to be Solved by the Invention) However, the conventional pink noise generator 1 used in the former method extracts the white noise output from the white noise generator through a -3 dB/octave filter. However, the level accuracy of the pink noise is controlled by the accuracy of the filter, which has the disadvantage that it is difficult to obtain a highly accurate level. Note that white noise refers to noise whose energy per unit bandwidth is constant for all frequencies. In other words, if we express energy characteristics by plotting energy on the vertical axis and frequency on a uniform scale on the horizontal axis, we will get a flat characteristic, but if we plot energy characteristics on a logarithmic scale on the horizontal axis, we will get a flat characteristic. The characteristic is that energy increases as the frequency increases with an octave slope. Therefore, in order to obtain the pink noise characteristics described above, it is necessary to attenuate the high frequency energy with a -3 dB/octave filter.

On the other hand, since the output signal of the wobble tone generator 6 used in the latter method is a frequency modulated wave, it is difficult to obtain a wideband signal wave with one output. It is necessary to output the frequency modulated signal by dividing it into
The measurement will take a considerable amount of time.

The present invention focuses on these points,
The purpose is to provide a pseudo pink noise generator that can obtain a pseudo pink noise signal with high accuracy and excellent reproducibility without using a filter and with a relatively simple circuit configuration.

(Means for Solving the Problems) The pseudo pink noise generator of the present invention includes a memory storing a plurality of sine waveform data of equal levels at logarithmically equal frequency intervals, and a memory for reading out the waveform data from the memory. The present invention is characterized by comprising: address generating means for generating an address; and a D/A converter for converting waveform data read from the memory into an analog signal in accordance with the address added from the address generating means.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In FIG. 1, 7 is a memory in which a plurality of logarithmically equal frequency intervals and equal levels of sine waveform data are stored, 8 is an address generator that generates an address for reading waveform data from this memory 7, and 9 is this memory. A D/D converter that converts the waveform data read out from the memory 7 into an analog signal according to the address added from the address generator 8.
It is an A converter.

As the memory 7, for example, a ROM is used. This ROM contains multiple n pieces with the following relationship: 〓 ⁿ⁼⁰ asin {2πα ⁿ _p・t+β(n)} Frequency _p α _p α ² _p ... Amplitude a a a... Initial phase β _p (random is preferable)... The sine waveform of is encoded and stored. Here, if α=2, then 1
There is one sine wave in the octave, α = 2
If it is 1/3, there will be one sine wave in 1/3 octave. Furthermore, as pseudo pink noise, it is desirable to have 10 or more waves in 1/3 octave.

As the address generation section 8, for example, an address counter that counts a clock having a constant period is used.

With this configuration, waveform data is sequentially read out from the memory 7 to the D/A converter 9 using the count value of the address counter as an address.
When passed through a bandpass filter having a 1/3 octave passband width, the energy frequency distribution characteristics become flat, and the signal is converted into an analog signal that can be used as pseudo pink noise.

With this configuration, there is no need for a conventional filter to attenuate the energy in the high frequency range of pink noise with high precision, the circuit configuration can be simplified, and high accuracy and reproducibility can be achieved. Can generate high pseudo-pink noise.

By the way, when waveform data is read from the memory 7 while changing the address at a constant cycle according to the clock, it is likely to be influenced by standing waves.

In order to eliminate the influence of such standing waves,
For example, the clock of the address counter 8 that generates the address to be added to the memory 7 may be frequency-modulated repeatedly at a frequency of about 5 Hz, or the address counter 1 may be used as the address generator 8 as shown in FIG.
It is sufficient to use one configured to read sine waveform data from the memory 11 according to addresses added from 0. In the latter case, it is also possible to integrate the two memories 7, 11.

Furthermore, by applying slow frequency modulation, resonance points in the acoustic space can be found efficiently.

(Effects of the Invention) As explained above, according to the present invention, a pseudo pink noise generator can obtain a pseudo pink noise signal with high accuracy and excellent reproducibility with a relatively simple circuit configuration without using a filter. can be realized, and the practical effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram showing another embodiment of the present invention;
FIGS. 3 and 4 are block diagrams of conventional sound field measuring devices, respectively. 7, 11...Memory, 8...Address generation section,
9...D/A converter, 10...Address counter.

Claims (1)

[Scope of Claims] 1. A memory storing a plurality of sine waveform data having the same level at logarithmically equal frequency intervals; an address generating means for generating an address for reading the waveform data from the memory; and the address generating means. A pseudo pink noise generator comprising: a D/A converter that converts waveform data read from the memory into an analog signal according to an address added from the memory.