When do I need to set a delay?

An audio retarder, as the name suggests, is an audio device that delays sound signal processing, especially commonly used for long-distance sound reinforcement. In fact, the role of delays is not limited to that. So, when do you need to use delay, and for what purpose?

The five main uses of audio delay

1. It is used to improve sound clarity during long-distance sound reinforcement

It can be said that the use of time delay in this regard is the most commonly used. In general, the outdoor sound reinforcement is relatively large, and the sound reinforcement distance is relatively long. If the sound is amplified simply using the main speaker so that the rear audience can hear it clearly, the sound pressure level in the front row will be extremely high. If the maximum sound pressure level at point A is 100dB from the distance from the speaker, then according to the formula SPL = SPLMAX-20LGR (SPLMAX = 100db) between the sound pressure level and the distance, it can be seen that each time the sound enhancement distance doubles, the sound pressure level decreases by 6dB, and then the sound pressure level of point B, 32 meters away from the speaker (r = 32m), should be only 70dB. There is a 30dB difference between the two, but in an actual sound enhancement environment, the difference in sound pressure level is even greater.

To avoid this phenomenon, the addition of a low-power make-up speaker is often used to avoid excessive sound pressure levels caused by the distance between the front and rear rows. Since the sound propagation speed is about 340 m/s, nearly 100ms passes through when the sound is transmitted to point B. The listener at point B will hear the sound of filling the speaker first, followed by the sound of the main speaker. In order to avoid this phenomenon, an audio delayer must be added before supplementing the power amplifier of the sound box, and thus extend the signal of channel B to achieve the effect of improving sound clarity. This is the most common use of audio delayers.

Of course, the thickness of the sound can also be increased using the reverb method, but the clarity will not be so good, and the intensity will also have a certain impact. Therefore, when clarity and intensity are required, delay processing is added instead of reverb.

2. Correct the difference when multiple speakers occur in multiple frequency bands

Among the rebar equipment, there are many large speaker devices. These speakers have a common feature, namely, most of them use multiple speaker designs to produce sound. The frequency responses of these speakers compensate each other in order to pursue a flat frequency response curve. But this design has certain drawbacks. As shown in Figure 2, the three speakers are A, B, and C. The diaphragms of the three speakers have certain position differences. This difference in position will cause different frequency bands to reach the human ear at different times.

Therefore, due to the time masking effect of the human ear, the human ear cannot properly receive the original sound signal, so that the brain cannot correctly distinguish the sound signal. In some cases, the sound lacks a slight response to mid-high frequencies. In order for the sound of several frequency bands to reach the human ear at the same time, it is necessary to delay both speakers B and C to restore the sound more realistically.

In this article, we focus on latency processing in this area.

3. Use delay for sound and image positioning

We know that the speed of sound propagation in the air is about 340 m/s, and during this propagation, there will be a time difference and intensity difference. Due to the occlusion effect, the loudness of the sound is large and the mask is small. The sound of approaching speakers will mask people in the distance; The human ear can judge the spatial orientation of a sound source by the difference in intensity and time of the sound source's signal.

The HAAS effect proves that when two sound sources emit exactly the same sound, the experience of binaural hearing differs depending on the amount of delay between one sound source and the other. When the delay between one sound source and another sound source is between 5ms and 35ms, the human ear can only perceive the presence of the sound source in front, and the sound image localization is biased towards the position of the front sound source, and there is no sound that can feel the lag. the presence of the source; When the delay is 30ms-50ms, the human ear can distinguish the presence of two sound sources, but the sound image is still located in the forward direction of the sound source; When the delay is greater than 50ms, the human ear can feel that two two sound sources are present at the same time, and the sound image is located at the location of the two sound sources.

3. Use delay for sound and image positioning

We know that the speed of sound propagation in the air is about 340 m/s, and during this propagation, there will be a time difference and intensity difference. Due to the occlusion effect, the loudness of the sound is large and the mask is small. The sound of approaching speakers will mask people in the distance; The human ear can judge the spatial orientation of a sound source by the difference in intensity and time of the sound source's signal.

The HAAS effect proves that when two sound sources emit exactly the same sound, the experience of binaural hearing differs depending on the amount of delay between one sound source and the other. When the delay between one sound source and another sound source is between 5ms and 35ms, the human ear can only perceive the presence of the sound source in front, and the sound image localization is biased towards the position of the front sound source, and there is no sound that can feel the lag. the presence of the source; When the delay is 30ms-50ms, the human ear can distinguish the presence of two sound sources, but the sound image is still located in the forward direction of the sound source; When the delay is greater than 50ms, the human ear can feel that two two sound sources are present at the same time, and the sound image is located at the location of the two sound sources.

In the case of the DBX 260 digital speaker processor, we can perform different delay processing on each channel of the 260 and feed it to different speakers. For example:

1. 260-1 channels of the output signal of the DBX 2 digital speaker processor are supplied to the subwoofer. Since the sound emitted by the woofer is low, there is a sense of hysteresis, so there is no need to delay two channels.

2. Channels 260-3 of the output signal of the DBX 4 digital speaker processor are provided to the main speaker. Of the three elements mentioned above, the main speaker is the second element, so there is no need to delay these two channels. Dispose.

3. Channel 260-5 of the output signal of the DBX 6 digital speaker processor is provided for the auxiliary speaker. Of the three elements above, the auxiliary speaker is the third. We can observe that if the auxiliary speaker and the main speaker are more than 20 meters apart, when the distance is more than 20 meters, we can consider delaying the auxiliary speaker. At this point, we only need to select the delay processing in the 260-5 channels of the DBX 6 and flexibly adjust it according to the delay distance or delay time. This is good.

In addition, when designing sound systems, many senior industry professionals have shown that it is best to use as few delay devices as possible. Whether it's in an outdoor or indoor soundstage, we can use centralized sound reinforcement whenever possible and then match the appropriate auxiliary speakers. The perfect sound system can be designed.

Delayed processing of indoor and outdoor rebar systems

Delayed processing of outdoor rebar systems

There are many large-scale outdoor performances. Because outdoor performances are often large in size, it is difficult to achieve consistent sound if distributed speakers are used for sound reinforcement. As a result, most large-scale outdoor performances currently use centralized sound enhancement methods and are not in the audience area. Set up auxiliary speakers to radiate the sound of the main speaker directly to the audience. If conditions are limited, an auxiliary sound box must be installed in the audience area. If the distance between the auxiliary speaker and the main speaker is 170 meters, according to the principle of sound 340 m / s, we can delay the signal delay time of the auxiliary speaker by 0.5 seconds, which is 500 milliseconds, so that the sound of the main speaker and the auxiliary speaker can reach the audience's ears almost at the same time, thus ensuring the consistency of the sound image. Of course, it is more troublesome to do so. Today, large line array loudspeakers are often used for outdoor mass performance, which can highlight sound and make the sound more focused.

Delayed processing of indoor acoustic reinforcement

Just like outdoors, in a large-area indoor acoustic reinforcement system, if the distance between the primary and secondary speakers is long, a delay-treated delayer is also required. Of course, lingering objects should be selected. The region where the primary audience is located is the primary region. Delay the secondary speaker close to the area. The delay time depends on the distance between the speaker and the primary speaker.

In fact, in most indoor sound reinforcement systems, there is no need to use a delayer due to the small area of the sound field, the distance between the speakers is not too far, which is why audio delayers are not available in widely used sound systems.