Check out this post by Joe Gilder on homestudiocorner.com which is aimed toward those who mix their own music at home. He explains how to use a reference mix, or how to use a professionally mixed track with your own homegrown work as you are in the process of mixing. Joe includes a brief description of how he does this. He concludes with a link where you can find further information about the method.
Worth a read for all would be mixers this weekend:
A Boring (But Effective) Way to Avoid Embarrassing Mixes
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I’m seeking info for sanctuary reverberation absorbsion material ( panels) and best placement.
There may be apps that do that. You can definitely find spectrum analyzers that will measure ultra low.
Is there an APP that can measure the ultra low frequency levels?