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TüN® 4 & MAX™: Using the True Delay Finder

A unique feature in TüN® 4 when paired with the MAX™ Audio Measurement system is the True Delay Finder. The True Delay Finder will measure an impulse response and report the time where the signal originated. Commonly found delay finders actually look for the peak (highest amplitude) of the impulse response and not the beginning. In a vehicle or room, reflected energy can actually be louder than the initial signal, so using a delay finder that measures the peaks, does not seem to work well in cars and rooms. The True Delay Finder attempts to locate the initial arrival of the signal. 

 

When using the True Delay Finder, a user can select from three different buttons. "Find Delay" - This button will measure the currently selected transfer function measurement (TF 3 by default) and report back the Measured Delay. "Insert" - This button will take the Measured Delay and insert it into the "Reference Delay" field. This will change the 0 in the center of the graph to the Measured Delay value. This way, a user can directly compare the next signal to the previous to determine if it is arriving earlier or later in time. The last button is "Insert Delta". This button will take the Delta delay and insert that into the selected channel of a connected JL Audio DSP. The Delta is the difference between the Reference Delay and the Measured Delay.

 

JL Audio TuN MAX Delay Finder DSP VXi MVi
Controls for the True Delay Finder

 

Before any measurements can be taken, follow the steps to make sure TüN® and MAX™ are properly configured to take measurements. Place the microphone array at the listening location and make sure the timing reference microphone (Mic 3 by default) is in the desired location. A test signal will be needed to determine the delay for each speaker. In TüN®’s Signal Generator, play Pink Periodic Noise. Switch to the Lin IR graph type using the Graph Type Combo Box in the upper left-hand corner of the graph window. It may also be helpful to hide the Targets if they are displayed within the Lin IR graph window. They can be hidden from the Input Combo Box which is in the upper right-hand corner of the graph window.

 

True Delay Finder in Action

When tuning a sound system, aligning the speakers in time will result in the best performance possible at a given location. The True Delay Finder can help to quickly align those signals in time. It is not possible to speed up time, but it is possible to delay it. In order to do this, a user will have to find the latest arriving signal and delay all of the sooner arriving signals to it. 

 

Begin by confirming that the Reference Delay field is set to 0. Next unmute the first channel and select
Find Delay. Since this is the first channel that has been measured, it is currently the latest arriving signal. This will become the Reference Delay. The user should select the Insert button to set the current delay value as the Reference. It may also be helpful to use the scale and zoom controls to zoom into the current data and visually confirm.

 

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Image shows channel A unmuted and Measured Delay field populated

 

Unmute the next channel and select Find Delay. If this value is larger than the value in the Reference Delay field, then this signal should become the new Reference Delay. It is also important for a user to understand how to analyze the Impulse Response. If the signal isn't visible, the True Delay Finder will not find it either. When looking at the Impulse Response, if the signal is arriving to the left of the Reference in the negative numbers, then that signal is arriving earlier. If the signal is arriving to the right of the Reference in the positive numbers, then that signal is arriving later. If the value reported by the True Delay Finder is not accurate, the user always has full control to manually adjust the values, or re-run the True Delay Finder. When the latest arriving signal is found, the user should set that as the Reference Delay and begin individually delaying the rest of the channels one at a time. Unmute another channel and select Find Delay, then select Insert Delta if using a JL Audio DSP product. If it is not a JL Audio product, the value can be manually added to another DSP. Do this for all channels to align all signal arrival times to the Reference Delay arrival time.

 

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Image shows Channel A set as Reference Delay

 

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Image shows later arriving signal on Channel B

 

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Image shows latest arriving speaker found and set as the Reference Delay

 

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Image shows Channel A aligned with Reference Delay after delay was added

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