Pressure limiter is short for compression and limiter.

Compressor: An amplifier whose gain decreases as the input signal level increases.

Limiter: An amplifier whose maximum output level remains constant after the output level reaches a certain value, regardless of how the input level is increased. The maximum output level can be adjusted as required.

Generally speaking, compressors and restrictors are often combined together, where there is compression function there will also be a restriction function.

Although the sound pressure of the singer's voice is limited, there is a very important factor that makes the signal level picked up by the microphone change very strongly. This factor is the distance between the microphone and the singer's mouth. The closer the distance is, the stronger the signal will be.

This change can sometimes reach far beyond the amplifier's limits, which can easily lead to top clipping distortion, which, of course, in addition to making a bad sound, can also burn out the tweeter speakers!

For most "amateur singers", they are very difficult to control this distance, so often hear because of too close, and there is excessive distortion, of course, the sound is very unpleasant, close to the broken throat growl.

The use of pressure limiter can basically solve this problem, avoiding the trouble caused by over-strong signal.

However, this feature is currently available only on more specialized devices.

Pressure limiter is generally divided into two main functions, that is: noise gate, compressor and limiter.

A, noise gate

1. Threshold

The noise gate, as the name suggests, reduces the normal noise in the system. Visually, it is like a sluice in a reservoir, but it intercepts the bottom sludge. If the sluice is too low, the silt in the water will flow down through the sluice. If the sluice is too high, it holds back not only useless mud, but also useful fresh water. So the THRESHOLD level, or THRESHOLD, of a noise gate has to be set just right, just like a sluice in a reservoir has to be set just right. Of course, in order to completely intercept the silt, we can properly improve the height of the sluice, so although also intercepted some clear water, but also to do safe, relatively speaking, is worth it.

2. Recovery time (Release)

A longer recovery time is conducive to the smooth transition of the signal, otherwise the recovery time is too short, there will be abrupt feeling, the sound will appear intermittent. Figuratively speaking: if we open our mouth to sneeze, because from opening to closing the mouth time is very short, so the sound is very abrupt, such a sound is easy to let people perceive; If we stretch and take a long breath when we are tired, then the time between opening your mouth and closing your mouth is longer. The sound you make is relatively smooth and transitional, and others will be less likely to notice this sound. This is also why we turn down the volume of music slowly, can not turn it off, because it is too abrupt, let a person feel uncomfortable. Release, and I'm going to explain it in terms of the electroacoustic principle that some people have a hard time understanding, so it makes sense.

B. Compressor and limiter

1. Threshold

The THRESHOLD gate in the noise gate is a very low sluice. It is at the bottom of the water inlet of the reservoir. Its main function is to block the silt flowing into the reservoir. The THRESHOLD sluice gate in the compressor is a higher sluice gate, which is on the top of the inlet of the reservoir. If the sluice gate is too high, the reservoir may be in danger of collapse. If the sluice gate is too low, the reservoir storage is not enough, so in order to achieve the maximum and safe storage, the sluice gate should be adjusted to the appropriate position. Therefore, the adjustment of the THRESHOLD is important, which determines the THRESHOLD at which the voltage limiter becomes active.

2. Compression Ratio

The compression RATIO is in line with the THRESHOLD, which is used to describe the sluice. A compression RATIO of 6:1 is like the upstream water flowing 6 meters beyond the safe range of a reservoir, but the water flowing into the reservoir is only 1 meter high after the pressure-limiting treatment, so the reservoir is still safe. For example, if the compression ratio is set to 4:1, a 4 dB increase in input level will only result in a 1 dB change in output level. When the compression ratio is set above 6:1, the compressor actually becomes a limiter. When the compression ratio is set to infinity :1(infinity), the output level will not change no matter how much the input level is increased. This is what the limiter does.

3. Start Time (Attack)

Start-up time is how long it takes for the voltage limiter to start operating when the signal level is above the THRESHOLD set by us, just like how long it takes for a gate to open. If the start time is too fast, it may slightly affect the dynamic and intensity of the music head; If the start time is too slow, it will affect the natural degree and transient of the music, and also produce a certain sense of delay and turbidity. Therefore, we should adjust the startup time to be a little shorter than the two.

4. Recovery time (Release)

The specific setting of this aspect should also be reasonably adjusted by referring to the start time (Attack) and music characteristics.

Three, the pressure limiter specific adjustment method

A, noise gate adjustment method

1. Threshold: When adjusting, pull down the total volume of the mixer, and there should be no artificial audio signal in the system. Turn the adjusting knob, and turn it up a little when you see the noise door indicating the red light, but not too high, otherwise the useful music will be suppressed. As in the case of the sluice above, it should be raised slightly above the standard level, even if some water is blocked.

2. Recovery time (Release) : the recovery time of the noise gate is slightly different from that of the compressor, which can be appropriately longer. Generally speaking, the recovery time should be around 500 ms.

B. Compressor and limiter adjustment method

Different pressure limiters have different adjustment knobs and parameters, but the following four points are the most basic standard function knobs for most pressure limiters:

1. Adjustment of Threshold

Want to combine compression ratio to adjust the adjustment of the THRESHOLD, the simplest way is to turn off the power amplifier, peripheral equipment before the pressure limit device to the normal working state, and then take the volume of the mixer to the normal performance of the location of the maximum volume, basically the tuning stage level signal indicator will be on a red light, then adjust the pressure limit THRESHOLD (THRESHOLD) of the knob and adjust to the pressure limit of compression indicating red light began to shine, says the pressure limiting device has started to work, then the THRESHOLD (THRESHOLD) is basic in tune. It should be noted that the compression ratio must be open, greater than 1:1, otherwise the pressure limiter is equal to straight through, is not any pressure limiting effect.

2. Setting of compression RATIO

The compression ratio should be set within a certain range. If the compression ratio is too small, it can not play a pressure-limiting role. If it is too large, the dynamic range of music will become narrow and the sound will be dry and tasteless. In a typical performance, the compression ratio can be set at about 3:1; In the system of taxi high dynamic audio signal, the compression ratio is generally set at about 5:1; When used as a limiter, the compression ratio should be set at infinity :1(infinite).

3. Adjustment of launch time (Attack)

We've already talked about how it's better to have a fast startup time, because it can affect the character of the music. Generally speaking, the starting time should be between 50ms and 80ms.

4. Adjust the recovery time (Release)

On the contrary, the recovery time needs to be slower, and the recovery time should be between 400ms and 600ms.

Pressure limiter adjustment method

Each single channel of the pressure limiter has 7 adjustment knobs from left to right, which are respectively:

1. Noise gate THRESHOLD level (THRESHOLD), which is set to a little more than 9 o 'clock on the clock;

2. The compression RATIO of the noise gate, which is set to 14 o 'clock on the clock;

3. Threshold, which is very important, is generally adjusted to the clock position of 13 o 'clock;

4. Compression RATIO: Generally, the performance system is adjusted to the position of 13 o 'clock on the clock, while the disco system is adjusted to the position of 14 o 'clock on the clock.

5. Start time (Attack), generally adjusted to 10 o 'clock position of the clock;

6. The RELEASE time is generally adjusted to the 14 o 'clock position of the clock;

7. Output Gain is generally adjusted to a little more than 12 o 'clock of the clock.

Note:

1. To make the limiter work, it is necessary to press the compression switch (COMP), or it is in the bypass state.

2. It is necessary to ensure that the peak indicator light flashes only when the signal is raised to the field amplifying size, otherwise the output level is not well adjusted.

3. It is necessary to ensure that the indicator level of gain reduction has a large flare when the signal is raised to the field amplifying size, otherwise the starting control threshold is not well adjusted.

4. Generally, the voltage limiter is connected behind the mixer. If the background noise of the system, such as hum, is large, the voltage limiter is put before the power amplifier or electronic frequency divider.

5. When the voltage limiter is used in stereo amplification, the stereo interlock switch (LINK) should be pressed. If the left and right channels are processed by different signal sources, it should not be pressed.