Hey guys, been doing a bit of research on measuring a vehicle and was wondering how to measure impulse response with a USB mic. I currently have a UMM-6. From what I gathered it isn't possible to get impulse response while using a usb mic for various reasons I didn't quite grasp. Saw a few people say to use a m audio transit or pre looked for some but they've been discontinued. Anyone wanna suggest an alternate solution?
Measuring Impulse Response with USB Mic
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If you are using Room EQ Wizard, then you are correct.... you cannot use the loopback as a timing reference while using a USB microphone.
I'm not sure about other software programs, however.
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Correct.
The loopback is used as a timing reference so that the impulse response measurements can be compared vs. a consistent time frame. This is useful for determining time alignment settings, and for comparing phase.
Not sure if I understand loopback entirely but you basically need l/r output and one output will be looped back to the measuring device? Not sure where I read it but I saw a mobile pre/transit would allow loopback with a usb mic. Anyone know if that would work?
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Not sure if "loopback" is the correct word...
Loopback is being able to use the same stream as output and input. For instance, a software which record the audio stream send on the output of your sound card. If your sound card has loopback you can do it directly by setting the sound card output as sound input in your software, if not you have to manually loop the signal back to the sound card input socket.
What you need for T/A calculation, is that your input device (the USB mic) and your output device (your sound card) both use the same clock signal. As far as I know, it is impossible with the UMM-6.
And for that you will probably need to buy a sound card that have both the output interface needed (RCA, SPDIF or TOSLINK) and the input interface (XLR with phantom power): usually when both are on the same sound card (internal or USB), they share the same clock signal.
The goal is that the output sound stream (send to your sound system) and the input sound stream (measured by your mic) have always the same time reference, so every mic measurement can be compared one to another: on all measurements, the same sample number correspond exactly to the same output time.
It's easy to test if your hardware use the same clock: put the mic in the car, and measure a full swipe. Wait a minute, and without touching anything else, measure a full swipe again.
It the first maximum peak impulse on both measurement are on the same sample, you're good to go. If not...
Loopback is being able to use the same stream as output and input. For instance, a software which record the audio stream send on the output of your sound card. If your sound card has loopback you can do it directly by setting the sound card output as sound input in your software, if not you have to manually loop the signal back to the sound card input socket.
What you need for T/A calculation, is that your input device (the USB mic) and your output device (your sound card) both use the same clock signal. As far as I know, it is impossible with the UMM-6.
And for that you will probably need to buy a sound card that have both the output interface needed (RCA, SPDIF or TOSLINK) and the input interface (XLR with phantom power): usually when both are on the same sound card (internal or USB), they share the same clock signal.
The goal is that the output sound stream (send to your sound system) and the input sound stream (measured by your mic) have always the same time reference, so every mic measurement can be compared one to another: on all measurements, the same sample number correspond exactly to the same output time.
It's easy to test if your hardware use the same clock: put the mic in the car, and measure a full swipe. Wait a minute, and without touching anything else, measure a full swipe again.
It the first maximum peak impulse on both measurement are on the same sample, you're good to go. If not...
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You can time-lock the clock in Holm. Measure the tweeter first in slot "a" then go under the "data" tab and check on "use time lock". Go back and measure the tweeter again under tab "b". That is your reference. Every measurement from then on should be "locked" to the second tweeter measurement. You can verify this by measuring the tweeter again at any time during the process like Zeblod explained. That method has worked for me on two different computers, however it might not work for you.
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Thanks man! I needed this piece of information!
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