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post #1 of 8 Old 03-03-16, 05:47 PM Thread Starter
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Impulse Response measurement

Forgive me if this is a stupid question, but I have been hunting for an answer on here and in the manual for a while now to no avail. I am trying to figure out how to take an Impulse Response measurement. Every time I attempt to run a measurement the sweep is extremely slow and not a short blip. It was my understanding that in order to get an accurate impulse response you need the "sweep" to be a short clap type sound that contains equal amounts of all frequencies? Is this incorrect? If so, how do I make REW output this type of signal. Thanks.
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post #2 of 8 Old 03-04-16, 03:32 AM
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Re: Impulse Response measurement

All REW measurements result in an impulse response. The help describes the particular log sine sweep method used.
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post #3 of 8 Old 03-04-16, 09:22 AM Thread Starter
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Re: Impulse Response measurement

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3ll3d00d wrote: View Post
All REW measurements result in an impulse response. The help describes the particular log sine sweep method used.
I know you can see the Impluse response from the sweep, but in order to properly "gate" a measurement for a quasi-anechoic frequency response the pulse needs to be sufficiently short to not excite room modes... unless I'm understanding this wrong...
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post #4 of 8 Old 03-04-16, 01:01 PM
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Re: Impulse Response measurement

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squiers007 wrote: View Post
I know you can see the Impluse response from the sweep, but in order to properly "gate" a measurement for a quasi-anechoic frequency response the pulse needs to be sufficiently short to not excite room modes... unless I'm understanding this wrong...
A true impulse, as you are suggesting, contains all frequencies from approaching DC to approaching infinite, so room modes are excited regardless.

The impulse response plot derived from a frequency response sweep via the Fourier transform is mathematically a perfect impulse response. It is not a "fake" or a "second rate" impulse response.

Depending on setup, the REW gating function allows one to focus on the direct signal without disturbances from reflections. Again, it is all done mathematically, but there is nothing "second rate" about its results.
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post #5 of 8 Old 03-04-16, 01:11 PM Thread Starter
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Re: Impulse Response measurement

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A true impulse, as you are suggesting, contains all frequencies from approaching DC to approaching infinite, so room modes are excited regardless.

The impulse response plot derived from a frequency response sweep via the Fourier transform is mathematically a perfect impulse response. It is not a "fake" or a "second rate" impulse response.

Depending on setup, the REW gating function allows one to focus on the direct signal without disturbances from reflections. Again, it is all done mathematically, but there is nothing "second rate" about its results.
I never meant to imply it was second rate or worse in any aspect, just different. But, based on your response I guess that was incorrect. So the impulse response I see from an REW sweep will be identical to one I see from say a measurement using HOLMImpulse? Meaning the FR data will be the same all else being equal?

I just want to make sure my measurement setup and techniques are as perfect as they can be and I'm more familiar with REW than HOLMImpulse which is why I asked. I don't want to be using "bad" FR data when designing a xover. Thanks in advance.
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post #6 of 8 Old 03-04-16, 01:23 PM
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Re: Impulse Response measurement

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squiers007 wrote: View Post
I never meant to imply it was second rate or worse in any aspect, just different. But, based on your response I guess that was incorrect. So the impulse response I see from an REW sweep will be identical to one I see from say a measurement using HOLMImpulse? Meaning the FR data will be the same all else being equal?

I just want to make sure my measurement setup and techniques are as perfect as they can be and I'm more familiar with REW than HOLMImpulse which is why I asked. I don't want to be using "bad" FR data when designing a xover. Thanks in advance.
HOLMImpulse's "chirp" is a shortened version of the sweep that REW uses, it is not a true impulse. HOLMImpulse uses the same technique as REW to calculate the impulse response plot from a sweep. It can be argued that REW's longer sweep is more immune to noise and will give a more accurate result.

Historically, a blank starter gun has been used by acoustical firms to generate a real impulse. Trouble is, a real impulse is infinitely high and infinitely short, impossible to generate accurately. The sweep and derived impulse is a much more accurate and manageable way to accomplish it.
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post #7 of 8 Old 03-04-16, 01:25 PM Thread Starter
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Re: Impulse Response measurement

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AudiocRaver wrote: View Post
HOLMImpulse's "chirp" is a shortened version of the sweep that REW uses, it is not a true impulse. HOLMImpulse uses the same technique as REW to calculate the impulse response plot from a sweep. It can be argued that REW's longer sweep is more immune to noise and will give a more accurate result.

Historically, a blank starter gun has been used by acoustical firms to generate a real impulse. Trouble is, a real impulse is infinitely high and infinitely short, impossible to generate accurately. The sweep and derived impulse is a much more accurate and manageable way to accomplish it.
Perfect, thanks for clarifying everything! Now I feel more confident my measurements were accurate. Thanks again.
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post #8 of 8 Old 03-04-16, 02:44 PM
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Re: Impulse Response measurement

That is also explained in the Getting Started help.
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