IR Windows and Impulse graph - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 24 Old 01-08-15, 12:11 AM Thread Starter
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IR Windows and Impulse graph

I am working with the IR window and the Impulse graph, but I am not sure if my impulse graph should look like this. It is looking so messy.

Also, I can't find out what the left and right windows mean and is there perhaps some advise or info available on what these different type of "algorithms" are good for like turkey 0.25?

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post #2 of 24 Old 01-08-15, 12:59 PM
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Re: IR Windows and Impulse graph

I've made this a separate thread since it doesn't relate specifically to the beta version.

It is difficult to tell a lot from the graph image since it only shows part of the response, if you attach the actual measurement file (the .mdat file) it will be much easier to check whether it is OK.

Different window shapes offer different trade-offs between resolution and artefacts arising from the truncating effect of the window, for most purposes you are best leaving the window types at REW's default settings. There is plenty of information about window functions in wikipedia, amongst other places.
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post #3 of 24 Old 01-08-15, 02:40 PM Thread Starter
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Re: IR Windows and Impulse graph

My apologies for posting in the wrong thread.

1 Sweep Surround A.mdat

Does the left Windows mean the mic left channel and the right the mic right channel?

Thank you for your help. I don't understand yet what all the controls do, but I am just beginning to learn.
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post #4 of 24 Old 01-08-15, 03:18 PM
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Re: IR Windows and Impulse graph

Left and right are relative to the Impulse peak, left is before and right is after.

The measurement looks fine. There is some activity in the impulse response before the peak occurs, though not enough to be a concern. That can sometimes be caused by sample rate conversion in the computer (for example, REW sample rate set to 48k when the soundcard is running at 44.1k or vice versa) and sometimes by FIR equalisers (like Audyssey or Dirac).
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post #5 of 24 Old 01-11-15, 03:33 PM Thread Starter
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How useable will my measurement be in building a FIR filter by using these USB audio devices. I am starting to believe that I have bought the wrong mic.
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post #6 of 24 Old 01-11-15, 07:55 PM
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What is it you want to accomplish with an fir filter? The first image you posted looks like an impulse taken at the lp
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post #7 of 24 Old 01-11-15, 08:14 PM Thread Starter
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I want to create a room acoustic filter for use in JRiver.

The measurement is that of a bookshelf speaker, on axis and at tweeter height, at 80 cm distance.
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post #8 of 24 Old 01-12-15, 12:08 PM
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You want to create a room correction filter at that close distance? Is that actually the listening distance? A measurement for room correction is taken at the listening position. A measurement as close as you've taken it is for speaker design/correction with a gated impulse.
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post #9 of 24 Old 01-12-15, 03:16 PM Thread Starter
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Do I not need to know my speaker response in order to find out what my room influence is?
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post #10 of 24 Old 01-13-15, 05:52 AM
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Well that depends on who you ask. I don't do any rc over about 400hz but if I did I would take into consideration the anechoic response. That said your ir looks too chaotic to be useful for a quasi-anechoic measurement. You need to get the speaker on a stand as far away from all boundaries that you can, and have the mic halfway between the floor and ceiling (assuming a typical 8' ceiling). Then you gate the data before the first reflection.
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