Acoustic Timing Reference Measurement

caseopia

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Hi John, i'm new to measurement.

And plan to do time alignment in my car audio using REW. For the info i'm using full active setup from a DSP.

My questions are:

1. If i'm using UMIK-1 as microphone. Can i get good result for time alignment? Since lot of people said UMIK-1 doesn't have any requirement for loopback ( i don't understand loopback for)?

2. Some said it still can be done using UMIK-1 with timing reference on the measurement menu at REW, if that so how i fill number on the timing offset box? (i put the picture as you can see)
since i saw on a youtube channel the value number fill with -1.8469.

Thank you.
Screenshot_1.png
 

John Mulcahy

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Using a USB microphone means it is not possible to have a loopback connection as a timing reference since there is nowhere on the microphone to connect the loopback. An alternative is to use the acoustic timing reference. That means REW sends out a timing signal on the channel chosen as the reference and uses the detection of that signal by the mic to define the reference time. However, in a highly reflective environment like a car detection of the timing signal arrival can be unreliable. It is not likely to give good timing results.

The timing offset depends on the distance from the reference channel to the mic and any processing delays in the signal path. REW can work out the figure to use using the "Estimate IR delay" option in the graph controls, that can update the offset for you.
 

sm52

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However, in a highly reflective environment like a car detection of the timing signal arrival can be unreliable. It is not likely to give good timing results.
I have used exactly acoustic synchronization in the car successfully. To determine delays. Not for equalizer.
 

caseopia

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I have used exactly acoustic synchronization in the car successfully. To determine delays. Not for equalizer.
Can you share the detail step by step on how to get good result?

Thank you
 

sm52

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I took measurements with an external sound card and a microphone connected to it. I have not dealt with UMIK connected to USB. Therefore, my actions may not help you, or confuse you.
 

caseopia

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I took measurements with an external sound card and a microphone connected to it. I have not dealt with UMIK connected to USB. Therefore, my actions may not help you, or confuse you.
Yes, UMIK-1 is all i can afford at the moment

And all i did (step by step guidance from any forums) were failed

I wanna knew if there is accurate way to do time alignment in car audio

Since some said using tape measure is also OK

I had tried it and the result of tape, gave me right stage in front of driver position (Right side)

I need to do Left channel adjusment (mostly reduce the milisecond delay)

To get center stage.

But as you know, tape measurement way is not pro tuner way to do time alignment

And many pro's in my country not willing to teach me

How to do their way for accurate time alignment in car audio
 

sm52

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Maybe with a UMIK connected to USB, it is possible to do this. You need to create 4 files in the REW generator window with a sampling rate of 48 kHz 16 bits, if your player allows such a frequency and bit depth. I packed 4 files in a zip archive that I use myself. Burn these files to CD or USB-flash, depending on what works in your player. How do you organize the division of frequency bands? Can you disable individual bands?
 

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caseopia

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Maybe with a UMIK connected to USB, it is possible to do this. You need to create 4 files in the REW generator window with a sampling rate of 48 kHz 16 bits, if your player allows such a frequency and bit depth. I packed 4 files in a zip archive that I use myself. Burn these files to CD or USB-flash, depending on what works in your player. How do you organize the division of frequency bands? Can you disable individual bands?
Yes my dsp can do individual bands, and i did measurement for each driver.

i'm using all of it with pink noise from IASCA CD

When i did left tweeter measurement for example. I mute other channels

So i can get the response from left tweeter only
 

sm52

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i'm using all of it with pink noise from IASCA CD
the IASCA disc was recorded with compression and then restored to wav. I do not recommend using it to evaluate the sound. Or for testing.
Disable all frequency bands in the DSP except for the tweeters. Unpack the files from the archive into a folder. If you have burned 4 files on a CD, connect the microphone to your computer, set REW to measure at 48kHz, go to the SPL measurement tab, click on the right middle 'from file', 'browse', and find the file L_ref_L.wav on your computer. Its name will appear below the window.
1.Click start in the measurement window. After that, click on the player to play the L_ref_L.wav file. The measurement will take place. When the graph appears, stop playback on the player.
2.After measuring on the top right, press 'controls', 'estimate IR delay', 'shift and update timing offset'.
3. Repeat step 1
You now have a left tweeter measurement with zero time. Starting point. Then select the R_ref_L.wav file using the 'from file' button, press start. Play the file with the same name on the player. After the graph appears, stop the player. This will be the measurement of the right tweeter relative to the left tweeter. Turn off the right tweeter band, turn on the right midrange band. Start the measurement in REW, then on the player. A graph of the right midrange relative to the left tweeter will appear. Turn off the right midrange band, turn on the right sub band. Take the measurement as before. A graph of the right sub relative to the left tweeter will appear.
Now load the R_ref_R.wav file into REW. Turn off all bands except the tweeters. Repeat everything from point 1, but for the left bands relative to the right tweeter.
Save all measurements. Attach to your post. I'll see what happens.
 

caseopia

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the IASCA disc was recorded with compression and then restored to wav. I do not recommend using it to evaluate the sound. Or for testing.
Disable all frequency bands in the DSP except for the tweeters. Unpack the files from the archive into a folder. If you have burned 4 files on a CD, connect the microphone to your computer, set REW to measure at 48kHz, go to the SPL measurement tab, click on the right middle 'from file', 'browse', and find the file L_ref_L.wav on your computer. Its name will appear below the window.
1.Click start in the measurement window. After that, click on the player to play the L_ref_L.wav file. The measurement will take place. When the graph appears, stop playback on the player.
2.After measuring on the top right, press 'controls', 'estimate IR delay', 'shift and update timing offset'.
3. Repeat step 1
You now have a left tweeter measurement with zero time. Starting point. Then select the R_ref_L.wav file using the 'from file' button, press start. Play the file with the same name on the player. After the graph appears, stop the player. This will be the measurement of the right tweeter relative to the left tweeter. Turn off the right tweeter band, turn on the right midrange band. Start the measurement in REW, then on the player. A graph of the right midrange relative to the left tweeter will appear. Turn off the right midrange band, turn on the right sub band. Take the measurement as before. A graph of the right sub relative to the left tweeter will appear.
Now load the R_ref_R.wav file into REW. Turn off all bands except the tweeters. Repeat everything from point 1, but for the left bands relative to the right tweeter.
Save all measurements. Attach to your post. I'll see what happens.
Will absolutely try.Thank you very much sir!

I will come again on 01/22/2023 to post the result here

Thank you once again for the guidance.
 

caseopia

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What did you manage to do?
It was failed.I'm trying to measure using your method.But my dsp won't connect to my laptop.Seems need to start over with the installation from basic.
 

carsound

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Jun 5, 2017
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Yes, UMIK-1 is all i can afford at the moment

And all i did (step by step guidance from any forums) were failed

I wanna knew if there is accurate way to do time alignment in car audio

Since some said using tape measure is also OK

I had tried it and the result of tape, gave me right stage in front of driver position (Right side)

I need to do Left channel adjusment (mostly reduce the milisecond delay)

To get center stage.

But as you know, tape measurement way is not pro tuner way to do time alignment

And many pro's in my country not willing to teach me

How to do their way for accurate time alignment in car audio


use acoustic reference, But you need use subwoofer or far speaker to reference, another speaker alignment ,

driver is right side , you need Increase right side delay , Tw and mid maybe 0.5ms, you can do center phantom image.
 

caseopia

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use acoustic reference, But you need use subwoofer or far speaker to reference, another speaker alignment ,

driver is right side , you need Increase right side delay , Tw and mid maybe 0.5ms, you can do center phantom image.
Yes since all cars in my country were right side driver. It will be subwoofer or Left midbass

As timing reference. And yes i just plan to use acoustic timing reference with REW and UMIK-1

But still confuse on RTA of my tweeters. The curve still won't drop under 100 Hz

Yet i change with other laptop, it drop below 3 Khz. I cannot understand

What's wrong with my laptop?
 

carsound

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Jun 5, 2017
Messages
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Yes since all cars in my country were right side driver. It will be subwoofer or Left midbass

As timing reference. And yes i just plan to use acoustic timing reference with REW and UMIK-1

But still confuse on RTA of my tweeters. The curve still won't drop under 100 Hz

Yet i change with other laptop, it drop below 3 Khz. I cannot understand

What's wrong with my laptop?
did you have any can show this issue picture?or data?
 
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