Pcoombs, you don't need a microphone for your comparison. The room and the microphone add too much coloration and don't add anything positive to the comparison. Simply plug the power cords into an amp or preamp and record thru the tape out circuit. You can even make alllowances for the power cord to settle in and then A/B to your heart's delight.
But some people think A/B comparisons are a problem.
Recording engineers use A/B comparisons every day. Which mic to use with this vocalists? Do a few test recordings with different mics and A/B listen to the results. It doesn't take days. At what level should the lead vocal be placed in the mix? Do a few different mixes while varying the vocal level and then A/B listen for what you think sounds right. There are nearly a countless number of decision like these in any recording sessions and engineers/producers/musicians rely upon an A/B comparison to determine what sound they want to use. And they don't take days to do it.
But some people think A/B comparisons are a problem.
a/bs have been discreditedand
a/b issue is loaded with difficulties because i do not think it is possible to absolutely control the variablesI suggest that you lack the imagination to design a limited variable A/B comparison. It's easily done. (I will admit that your use of the word "absolutely" does give you wiggle room.) The hard part, as with most experiments, is interpreting and drawing conclusions from the data.
Recording engineers use A/B comparisons every day. Which mic to use with this vocalists? Do a few test recordings with different mics and A/B listen to the results. It doesn't take days. At what level should the lead vocal be placed in the mix? Do a few different mixes while varying the vocal level and then A/B listen for what you think sounds right. There are nearly a countless number of decision like these in any recording sessions and engineers/producers/musicians rely upon an A/B comparison to determine what sound they want to use. And they don't take days to do it.