Measuring correct delay time

In this section we will discuss why we should be interested in measuring delay time and how this can be done using WinMLS


When calibrating a surround system, one of the issues is to find is the delay time from each loudspeaker position to the measurement position. This must be found, since the surround system processor can correct for this delay time and thereby improve the sound quality. You can find this delay time by measuring the distance, but it can also be found using WinMLS. How to find this using WinMLS will be explained next.


The challenge when measuring delay is that many sound cards usually do not start to record and playback simultaneously, and this delay between playback and record is usually not constant. Exceptions to this are the Lynx, Card Deluxe, Siena/Marc 8 and Vxpocket/VX222 sound cards. Read more about this in the Sound cards section and the Measurement->System Delay… section.


If you have one of the sound cards mentioned above, the delay can easily be measured, but the delay of the sound card AD/DA converters gives an extra delay of about 1 ms. This delay can be corrected. The following sections explain the various method of measuring the correct delay.


Note that this will not correct for the delay of the sound card AD/DA-converters, which usually is from 10 to100 samples. Removing this delay is the second problem if one wants to measure the exact distance from the loudspeaker to the microphone. As an example, a loop-back measurement of the Soundblaster Extigy sound card is shown below. We see that it is 40 samples long and in the right figure below we have changed the x-axis to meters to see that it is equal to ~0.29 meters.




In this case, the loudspeaker-microphone distance result measured will be 40 samples too long since the sound card AD/DA-converters increases it. This delay can be corrected by subtracting 40 samples from the initial time delay measured when measuring the loudspeaker-microphone distance.


Corrections can be made automatically. To do this, you must correct for the delay of the sound card. The easies way of solving the problem with the delay is explained in Measurement walk-through 4 where channel two is used as reference. You may go directly to this part and skip the next of this part. You may alteratively go to Measurement walk-through 5 where a correction measurement is used to get the correct delay.


Finding delay from Time Data plot type

Delay/Distance from Parameters plot type

Delay from Room Acoustics plot type

Delay from Group Delay plot type

Delay from Frequency Response - Spectrum plot type