How to use the “ Delay” function in the digital processor?

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 the delay value can only be entered as a positive value, not a negative value. Therefore, when using the delay function:

 

The first method step

 

1. Measure the time required for each unit (speaker or speaker system) to reach the reference test point, and make a record;

 

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

 

3. Measure the transmission time of other units separately, and input the time difference into the delay data box 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 crossover point), calculate the delay in one cycle through the formula: (1000/Fc)×(θ/360)=Td, and The phase coincidence can be completed by adding to the unit that needs delay. Of course, you can also observe the overlap of the two phase curves while adjusting the delay data.

 

(Note: Fc is the acoustic crossover point, the unit is Hz; θ is the phase difference value, the unit is degrees °; Td is the delay time, the unit is milliseconds)

E.g:

 

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

 

2. Capture the ultra-low curve and insert 15ms in the measurement software delay box;

 

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

 

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 again in the processor. The value is (1000/100)×(90/360)=2.5ms, that is, 10+2.5=12.5ms.

 

Steps of the second method

 

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

 

2. To find the full frequency or ultra-low delay, insert either of the corresponding delays in the software delay box;

 

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

 

4. Subtract the smallest value of all from 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 crossover point), calculate the delay in one cycle through the formula: (1000/Fc)×(θ/360)=Td, and The phase coincidence can be completed by adding to the unit that needs delay. Of course, you can also observe the overlap of the two phase curves while adjusting the delay data.

 

(Note: Fc is the acoustic crossover point, the unit is Hz; θ is the phase difference value, the unit is degrees °; Td is the delay time, the unit is milliseconds)

 

E.g:

 

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

 

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

 

3. Finding the ultra-low delay is 115ms, the calculated difference is -10ms, and subtracting 10ms from the preset value of the ultra-low channel in the processor, the result is 90ms;

 

4. The full frequency channel of the processor is 100-90=10ms, and the ultra-low channel 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 again in the processor. The value is (1000/100)×(90/360)=2.5ms, that is, 10+2.5=12.5ms.

 

For ease of understanding, we simplified 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.

 

Note:

We often find that the use of Smaart's Find function is always unable to accurately capture the delay value of the subwoofer. There are two main reasons:

 

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

 

2. The arithmetic capability of the audio measurement software Smaart Find function is limited.

 

Reference measurement method for subwoofer delay:

 

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

 

2. Place full-range speakers at the same position for measurement (using 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).