Those things with signal to noise ratio
What is the signal to noise ratio?
From the literal meaning we can understand the ratio of signal to noise. The signal-to-noise ratio “letter†actually refers to the signal that is useful to the system. What is the signal that is useful to us in the language sound reinforcement system? In fact, the useful signal is the voice signal that enters the pickup. The “noise†word of the signal-to-noise ratio actually refers to a signal that is not useful to the system, and usually includes ambient noise entering the pickup, some noise caused by poor system line contact, and the like.
Methods and advantages and disadvantages of improving the signal-to-noise ratio of speech systems?
There are three common ways to improve the signal-to-noise ratio of a speech system. The first is to shorten the distance between the speaker and the pickup. The second is to increase the level of the pickup by gain. The third way is to reduce unwanted noise signals.
The first requires the speaker to be closer to the pickup, so the experience for the speaker is not very good, and it is necessary to stay close at all times to make the speaker appear restrained.
The second type can amplify the speech signal by increasing the gain of the pickup, but at the same time, the ambient noise will increase accordingly, and the system is highly prone to acoustic feedback.
The third is the most effective method to effectively improve the system signal-to-noise ratio by reducing the noise signal and highlighting the speech signal.
What DSP can improve the signal to noise ratio?
The most common DSP for improving the signal-to-noise ratio of the system is the noise gate and the expander. The noise gate can eliminate the environmental noise well in the system application. However, in the voice system, the same pickup is often not fixed due to the speaker, and some people have sound signals. Larger, some people have smaller sound signals. If the person with less sound is in front of the pickup with noise gate processing, the vocal may be intermittent, and the word head may be lost when the noise door is opened. The expander can well avoid this phenomenon and achieve a better live experience.
Really recognize the expander
There are two types of expander's two types of expanders, one is to amplify a signal below the threshold by a certain ratio, and the other is to reduce the signal below the threshold by a certain ratio. The detailed application of the second expander will be explained here.
Section | | Analysis <br> Reference: US Symetrix
Reference material: The expander used in this article is the expander module in the US Symetrix digital audio processor products. The expanders of the imported audio processor products on the market are all the same algorithm, so we can understand and use the same method. Expander features for each brand.
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Most new installation and commissioning engineers do not know the expander. Here, you will get a detailed understanding of the expander's graphics functions and the meanings of the various debug parameters.
From the above figure we can see a coordinate. The X axis represents the level of the input signal and the Y axis represents the level of the output signal. The green line segment in the coordinates represents the relationship between the input and output under the current parameter settings.
Debug parameters
Threshold: Threshold, indicating that a signal set below the threshold will be reduced by the ratio.
Ratio: Ratio means that when the input signal is lower than the threshold, it will decrease according to the set value. The input signal above the threshold is output in 1:1.
Attack: Start time, which indicates how much time is required to reach the set output level when the input level is below the threshold.
Release: Recovery time, indicating how long the input signal is greater than the threshold to reach 1:1.
Application examples and debugging methods of expanders
Figure 1
(Figure 1) Take the Composer programming software of the Symetrix network version as an example. The pink noise generator is used to simulate the ambient noise, and the ambient noise is eliminated by the expander.
Figure II
Step 1: Turn on the meter to see the noise level before entering the expander. (Figure 2) We can see that the noise level entering the expander is -36.9dB, and the signal level output from the expander is also -36.9dB, which means that the current expander status is 1:1 or Bypass.
Figure III
Step 2: Set the expander threshold to be higher than the pre-processing level according to the pre-processing level, for example, set to -24dB. Then set the ratio to 2. (Fig. 3), we can see that the signal with the input signal level of -37.4dB enters the threshold of -24dB, and the output level of the ratio is 2, the output level becomes -50.5dB. .
Figure 4
Step 3: Looking at the output level meter and increasing the ratio of the expander at the same time, we will find that the larger the ratio, the smaller the output level until the output level is lower than -72dB. The noise entering the system is eliminated (Figure 4).
Through the above three steps, we can eliminate the noise entering the system, but we will adjust the threshold more carefully when the voice system is on-site debugging. The correct threshold setting is to ensure that the noise is normal while keeping the voice normal. Passed without the occurrence of a stutter. The correct setting for the threshold should be set to a center level value that is above the noise level and below the speech level.
The correct use of the expander can effectively improve the system signal-to-noise ratio, so that the voice sound reinforcement system has a larger dynamic range, thereby improving the speech intelligibility of the voice sound reinforcement system. Let the conference participants fully and clearly understand the speaker's speech content, so as to achieve a good voice amplification effect.
—— Summary
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