Let me start by apologizing for the length of this post.
"I have made this longer than usual because I have not had time to make it shorter." Blaise Pascal

Interesting topic explained how to do a NULL Test

[GALLERY=media, 406]Mastered for iTunes 'sounds closer to CD' - I'm calling BS - UPDATED - YouTube by audiokid posted Apr 5, 2015 at 10:32 PM[/GALLERY]

With permission from Lavry Engineering:

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Regarding "Null testing"-

Basically; null tests are useful to determine if two files are identical. If they are different; you hear only the difference.

running a null test

Null: undefined, empty, or meaningless value.

Examples in Micing techniques to reduce bleed or unwanted standing Waves: Always aI'm the null of the polar pattern at the offending noise source. For example, if recording a snare drum aI'm the null of the mic at the high-hat to reduce high-hat leakage into the snare mic.

A small area or space where direct and reflected RF signals from a transmitter cancel each other, resulting in little or no usable energy being available to a receiver antenna.