Measuring Time Delay in a Mic Array

Measure time delay in microphone arrays with SoundCheck! In this video, we’ll show you how to calculate both absolute and relative record delays across multiple microphones for more accurate, time-aligned measurements.

Additional Resources for SoundCheck

Detailed explanations of how to use SoundCheck can be found in the SoundCheck manual.

Video Transcript: Measuring Time Delay in a Mic Array

When we make an audio measurement, there is always a time delay between the stimulus playback and the recording. We call this “record delay”. In a mic array, each microphone has its own record delay and sometimes you need to know the absolute delay between each mic and the stimulus, or the relative delay between each mic using one of them as a reference.

Here is a simple sequence to calculate the absolute delay. 

I play a sweep through my speaker. There’s a play and record acquisition step which records simultaneously on three calibrated microphones in my array, mic one, mic two, and mic three, so I get three recorded time waveforms from this step.

Let’s run the sequence up to this break-point here…

Now you can see we have our three three recorded time waveforms in the memory list. I’ve grouped these and labelled them RTWs. 

Next we use an analysis step to calculate the delay or the record delay between these microphones. Any of these analysis algorithms can be used as they all output the delay value for the waveforms.

To find the absolute delay for these microphones, we’ll use the stimulus itself as the stimulus waveform and the group of three RTWs as the response. When I click apply, I get record delay values for the three microphones. 

Now I’ll remove this break point and run the entire sequence one more time. We hear the stimulus; it’s recorded simultaneously on the three microphones, and the display shows the fundamental response for each microphone along with the record delay values. These record delay values can be represented as time in seconds, or in inches or samples. 

Now let’s calculate relative delay. We’ll use mic 1 as the reference mic, and calculate the relative delay of mic 2 and mic 3 compared to mic 1. 

To do this, let’s use the recorded time waveform for mic 1, since it’s my reference, as the stimulus in the analysis step. And we’ll use other recorded time waveforms as the response. Let’s run the sequence. 

Now you see that I get the record delay values compared to the first mic. Mic 1 is showing a delay of zero as that’s the new reference point.  Mic two has a time delay of 90.7 microseconds, compared to mic one, and mic three has a record delay of 68 microseconds.

This concept of using a non-stimulus waveform as the reference in the analysis step is a valuable technique with many other applications in audio test, for example, dual channel impedance measurements.