Multi-Mic Option Questions

[Chuck Gerlach]

How does REW handle the timing reference when using multiple mics? Since what I would end up with is an "average response", how can I also have a timing reference? And without a timing reference how would the Speaker Alignment Tool work?

What hardware would you recommend to interface between the multiple mics and REW on my computer?

 

[John Mulcahy]

REW listens for the timing reference on the first mic input. There is an option to generate individual measurements for each mic along with the average. Those could be cross-correlation aligned (requires V5.20.14) and vector averaged to produce a signal with an impulse response that could be used for alignment, but speaker alignment would probably work better with a single measurement at the listening position. Any audio interface that has multiple analog mic inputs could be used. The Focusrite 18i20 and Behringer UMC1820 have 8 mic inputs, for example, the Focusrite 18i8 has 4.

 

[Chuck Gerlach]

Thank you. Just ordered theFocusrite 18/20 - and more microphones !! And a carrying case. And some foam padding.
And some .......

 

[Chips Davis]

REW listens for the timing reference on the first mic input. There is an option to generate individual measurements for each mic along with the average. Those could be cross-correlation aligned (requires V5.20.14) and vector averaged to produce a signal with an impulse response that could be used for alignment, but speaker alignment would probably work better with a single measurement at the listening position. Any audio interface that has multiple analog mic inputs could be used. The Focusrite 18i20 and Behringer UMC1820 have 8 mic inputs, for example, the Focusrite 18i8 has 4.

If using multi mics in a larger area or large hall, there can be a difference between the levels that each mic is receiving, i.e., when averaging the spectrums, the weighting of each mic’s contribution may be major or minimal. If there is ten dB difference between mics, that mic will have very little influence on the average. Will you ever have the ability to adjust the levels for a more accurate large room spatial averaging? I’d be happy to pay extra for it and STI.
When using multi mic averaging, is it a “power average” or an “arithmetic average”?

 

[John Mulcahy]

There is an option under "Configure average" to align the SPL from each mic, either to the overall average SPL or to a specific SPL target. Averaging is rms.

 

[manton]

…If there is ten dB difference between mics, that mic will have very little influence on the average.

In addition to the REW weight method John mentioned, you could do additional measurements from the position of interest which will naturally give it more weight in the average.