# USB Mic Acoustic Timing



## Phillips (Aug 12, 2011)

Hi please can someone point me in the right direction cant seem to find instructions?

OS Windows XP

Thanks in advance


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## JohnM (Apr 11, 2006)

Measuring with a timing reference.


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## Phillips (Aug 12, 2011)

Hi John thanks

So select Acoustic Timing Reference in the preferences and leave selected for all measurements for now on?

Is there anything else I should select/change in the preferences?

Thanks again


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## JohnM (Apr 11, 2006)

Phillips said:


> So select Acoustic Timing Reference in the preferences and leave selected for all measurements for now on?


Select it when you need an acoustic timing reference for a measurement



> Is there anything else I should select/change in the preferences?


No


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## Phillips (Aug 12, 2011)

JohnM said:


> Select it when you need an acoustic timing reference for a measurement
> 
> No


Thanks John 

So just select for one measurement then unselect for the rest?

Thank again


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## JohnM (Apr 11, 2006)

That really depends on what it is you are trying to do. If you want measurements that showing timing relative to a reference, turn it on. If you don't, turn it off.


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## Phillips (Aug 12, 2011)

Hi John thank you.

Here is a step by step from Minidsp 
Is this for HDMI?
https://www.minidsp.com/applications/auto-eq-with-rew/measuring-time-delay

In the preference soundcard panel I have set the following is this correct?
I have not got HDMI and are using Java

Output Device = O/S soundcard (not sure what it is called
Output = Default
Channel = Right

Input Device = UMIK
Input = Default
Channel = Left


Thanks again


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## JohnM (Apr 11, 2006)

As a general point, do not leave the input and output on default, set them to the option offered in the drop-down menu.

What are you trying to achieve by making measurements with a timing reference? If you can explain what you are trying to do it will be easier to understand whether the acoustic timing reference will help and, if so, how you should use it.


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## Phillips (Aug 12, 2011)

JohnM said:


> As a general point, do not leave the input and output on default, set them to the option offered in the drop-down menu.
> 
> What are you trying to achieve by making measurements with a timing reference? If you can explain what you are trying to do it will be easier to understand whether the acoustic timing reference will help and, if so, how you should use it.


Thanks John

I am trying to set the distance in the receiver for time alignment.

Thanks again


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## JohnM (Apr 11, 2006)

Alignment of which speakers? If it is the main speakers and/or surrounds, use a tape measure. If it is the sub then the acoustic timing reference will not be helpful as it cannot accurately determine delays for subwoofers. There are other threads on setting sub delays, such as this one.


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## Phillips (Aug 12, 2011)

JohnM said:


> Alignment of which speakers? If it is the main speakers and/or surrounds, use a tape measure. If it is the sub then the acoustic timing reference will not be helpful as it cannot accurately determine delays for subwoofers. There are other threads on setting sub delays, such as this one.


Hi John thank you

Yes it is for the mains and surrounds.
Is the acoustic reference not suited for this?
If not please explain what its purpose is.

Thanks again


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## JohnM (Apr 11, 2006)

It could be used for that, but it will take a lot longer than just using a tape measure as with Java drivers you can only send signals to the left or right channels so you will have to manually shift connections to the other channels somehow.


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## Phillips (Aug 12, 2011)

JohnM said:


> It could be used for that, but it will take a lot longer than just using a tape measure as with Java drivers you can only send signals to the left or right channels so you will have to manually shift connections to the other channels somehow.


Thanks John to measure the surrounds I would need to use 90 degree file?
Also SPL would need to use the 90 degree file?

What is the Acoustic Reference main purpose?

Thanks again


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## JohnM (Apr 11, 2006)

Use the 90 degree file if you point the mic straight up, use the zero degree file if you point the mic at the speaker you are measuring.

The timing reference allows different measurements to be compared or combined in magnitude and phase as they share a common timing reference.


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## Phillips (Aug 12, 2011)

Thanks John

I measured all speakers and they all said -200mm delay (in the info panel), except for the left speaker (which is the reference channel). It read -750mm, but when re-measured it also said -200mm, re-measured again and back to -750mm, what could this be?

Thanks again


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## JohnM (Apr 11, 2006)

The reference channel should measure zero, it can't be delayed relative to itself. What frequency range did you measure over? Was any other channel playing at the same time?


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## Phillips (Aug 12, 2011)

JohnM said:


> The reference channel should measure zero, it can't be delayed relative to itself. What frequency range did you measure over? Was any other channel playing at the same time?


Hi John 0-20,000hz + only left channel playing

Could it be the computer, its old?

I left the Acoustic Timing selected for all measurements.

Thanks


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## JohnM (Apr 11, 2006)

I'm not sure what could cause that. If you post an mdat with a measurement of the left and right channels there might be some clue there.


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## Phillips (Aug 12, 2011)

Hi John when looking at the impulse and comparing 2 measurements, should I be looking at the biggest peak/negative or where it reaches 100.
Sometimes it doesn't reach 100

Thank you


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## JohnM (Apr 11, 2006)

The biggest, but the biggest should always reach 100% or 0 dB if the impulse graph controls are set to normalise to the peak.


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## Phillips (Aug 12, 2011)

JohnM said:


> The biggest, but the biggest should always reach 100% or 0 dB if the impulse graph controls are set to normalise to the peak.


Thanks John

It seems to be sometimes a smaller negative peak then a larger negative peak is this normal?

I have looked back on other measurements and sometimes the biggest peak has gone from negative to positive with absolutely nothing changing other than possibly mics or postioing. Im confused why this could happen

I'm I doing something wrong?

Thanks again


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## JohnM (Apr 11, 2006)

Phillips said:


> It seems to be sometimes a smaller negative peak then a larger negative peak is this normal?


Yes



> I have looked back on other measurements and sometimes the biggest peak has gone from negative to positive with absolutely nothing changing other than possibly mics or postioing. Im confused why this could happen


The overall sum of signals varies with position.



> I'm I doing something wrong?


Probably not.


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## Phillips (Aug 12, 2011)

Hi John thank you

Even with small mic positioning it change from a peak to a negative?

I am trying to see if my centre is out of phase. This is a negative 

Thank you


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## JohnM (Apr 11, 2006)

it is difficult to comment on without measurement files.


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## Phillips (Aug 12, 2011)

Hi John I have checked the polarity and it is connected correctly but the graphs shows incorrect polarity.

I have swapped the wires and polarity is good now, according to the graphs

Is it common that the internal wiring has been incorrectly wired?

Sorry at the moment I cant post files

Thanks again


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## Phillips (Aug 12, 2011)

Hi John to setup up the timing acoustic do I leave all the measurements with Acoustic Timing selected?

Thanks


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## JohnM (Apr 11, 2006)

Sorry, I don't understand the question.


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## Phillips (Aug 12, 2011)

JohnM said:


> Sorry, I don't understand the question.


Hi John e.g. Left Main is reference do I measure with Acoustic Timing (in preference's) ticked for all measurements including the reference (in this case Left Main)?

Thanks


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## JohnM (Apr 11, 2006)

Yes, keep it selected for any measurement that you want to have timing for.


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