# Latency (Delay) Compensation calibration



## raptor18 (Mar 11, 2011)

Hi.

According to Fuzz measure, you need to calibrate the Latency (Delay) for the system:

support.supermegaultragroovy.com/kb/fuzzmeasure/obtaining-accurate-delay-and-distance-values

When i do a soundcard calibration (with a loopback connection from output to input), is that included or must i make a separate calibration for that?


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## raptor18 (Mar 11, 2011)

Can i see this anywhere on my soundcard calibration file?


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## JohnM (Apr 11, 2006)

To allow for soundcard and OS latencies in REW make a loopback connection on the unused input channel and tick the "Use Loopback as Timing Reference" box in the Analysis Preferences. See Analysis Preferences for more info.


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## raptor18 (Mar 11, 2011)

It sounds as if the loopback must be connected during measurment.
Have i understood this wrong?


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## JohnM (Apr 11, 2006)

raptor18 said:


> It sounds as if the loopback must be connected during measurment.


Correct


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## raptor18 (Mar 11, 2011)

There is always one input channel over because the mic is always mono. But how about the outputs. Left and Right speak and voila, i'm out of outputs. Can i use any other output from my soundcard (i have 10 outputs) and still be able to use both speakers during measurment ?

/Raptor


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## JohnM (Apr 11, 2006)

No, the REW test signal is only generated on the left and right outputs. If you need to drive both speakers and also have an absolute timing reference then a simple splitter will do the trick. The absolute timing reference is usually only required if you need absolute times, for example if trying to time align different drive units in a speaker or different speakers.


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## raptor18 (Mar 11, 2011)

Ok, so for most cases, the timing compensation is not really needed?

I don't need to time align different drive units in a speaker or different speakers


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## JohnM (Apr 11, 2006)

raptor18 said:


> Ok, so for most cases, the timing compensation is not really needed?


That's right. Also in most cases you would not be driving both speakers at once when making a measurement. That can be useful when looking at low frequencies, as bass content is often mono and the room reacts differently with two sources than one, but for full range measurements having two speakers running typically makes the picture more confusing as the slightest difference in their distances from the mic will generate comb filtering.


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## raptor18 (Mar 11, 2011)

Thanks

I'm starting to understand the deal with using one speaker for measurment.

First, i thought you did a measurment to understand how your room "sounds". This cearly requires both speakers to be driven.

Now i understand it as you should use such tools to understand how your room reflects signals (sound waves) and such which really means that driving two speakers isn't really necessary. In best cases, the difference how sound travels between speaker 1 and 2 should be minimal.

Am i understanding this correct?


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## JohnM (Apr 11, 2006)

Sort of. At low frequencies, where the wavelength of the sound is comparable to the dimensions of the room, it is helpful to run both speakers as their combined effect can be significantly different from either operating alone and in much music the low frequencies are more or less mono so both speakers will be reproducing the content. At higher frequencies the speakers can be considered independently and measuring them alone gives a clearer picture of how each speaker is behaving and is affected by its environment (nearby surfaces and treatments etc).


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