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22

2022

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03

How to use the "delay" function of the audio processor

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The delay in the audio processor is a function often used by sound reinforcement system engineers. Here we briefly summarize the main methods of adjusting the delay.

We know that only positive values ​​can be entered for delay values, and negative values ​​cannot be entered. Therefore, when using the delay function:

first method step

1. Measure and record the time it takes for each unit (speaker or speaker system) to reach the reference test point;

2. Take the unit corresponding to the maximum value as a reference, capture its response curve, and insert the measured time into the measurement software;

3. Measure the transmission time of other units respectively, and input the time difference into the delay data frame of the audio processor according to the difference prompt automatically calculated by the measurement software.

4. According to the phase angle difference between the two units at the acoustic crossover point (frequency cross point), the delay in one cycle is calculated by the formula: (1000/Fc)×(θ/360)=Td, and Phase coincidence can be accomplished by adding to the units that need delay. Of course, it is also possible to observe the coincidence of the two phase curves while adjusting the delay data.

(Note: Fc is the acoustic frequency division point, the unit is Hertz Hz; θ is the phase difference value, the unit is degree°; Td is the delay time, the unit is milliseconds)

E.g:

1. The measurement result is 5ms for full frequency channel and 15ms for ultra-low;

2. To capture the ultra-low curve, insert 15ms into the delay box of the measurement software;

3. Measure the full frequency, find the delay, and input the calculated delay difference of the full frequency channel in the processor to 10ms;

4. If the phase curve corresponding to the acoustic crossover point is: the full frequency is at the top, the ultra-low is at the bottom, the crossover point is 100Hz, and the phase difference is 90 degrees. At this time, it is necessary to add a delay for the full frequency in the processor again. The value is (1000/100)×(90/360)=2.5ms, that is, 10+2.5=12.5ms.

Second method steps

1. Input a fixed delay value for each channel in the processor in advance, such as: 100ms;

2. Find the full-frequency or ultra-low delay, and insert any corresponding delay of the two into the software delay box;

3. Measure and find, increase or decrease the calculated difference on the original value in the processor;

4. Subtract the smallest value from all of them on each channel to get the final delay value;

5. According to the phase angle difference between the two units at the acoustic crossover point (frequency cross point), the delay in one cycle is calculated by the formula: (1000/Fc)×(θ/360)=Td, and Phase coincidence can be accomplished by adding to the units that need delay. Of course, it is also possible to observe the coincidence of the two phase curves while adjusting the delay data.

(Note: Fc is the acoustic frequency division point, the unit is Hertz Hz; θ is the phase difference value, the unit is degree°; Td is the delay time, the unit is milliseconds)

E.g:

1. The full-frequency and ultra-low channels in the processor are preset with a delay of 100ms respectively;

2. Find the full frequency delay of 105ms, and insert 105ms into the delay box of the measurement software;

3. Find the ultra-low latency of 115ms, calculate the difference as -10ms, subtract 10ms from the preset value of the ultra-low channel in the processor, and the result is 90ms;

4. The processor's full frequency channel is 100-90=10ms, and the ultra-low channel is 90-90=0ms;

5. If the phase curve corresponding to the acoustic crossover point is: the full frequency is at the top, the ultra-low is at the bottom, the crossover point is 100Hz, and the phase difference is 90 degrees. At this time, it is necessary to add a delay for the full frequency in the processor again. The value is (1000/100)×(90/360)=2.5ms, that is, 10+2.5=12.5ms.

For ease of understanding, we simplify the frequency band into two parts: "full frequency" and "ultra low". For more frequency bands, such as: high, medium, low, and ultra low, the above methods are also applicable, especially the second method, It is very easy to apply.

Notes:

We often find that the delay value of the subwoofer cannot be accurately captured using Smaart's Find function. There are two main reasons:

1. The wavelength of the ultra-low frequency sound wave is long, and it is easy to cause reflected sound in the actual application environment, and the measurement MIC is outside the reverberation radius;

2. The computing power of the Smaart Find function of the audio measurement software is limited.

Subwoofer delay reference measurement method:

1. Use the IR (Impulse Response) impulse response function to measure;

2. Place full-range speakers at the same position for measurement (use Find or IR impulse response function);

3. Use a tape measure or laser rangefinder to measure (the conversion result needs to be added to the system delay, mainly from A/D and D/A conversion).