How to level match when comparing components?

I diagree with ojgalli as to the reasoning.
He is doing an immediate and sudden comparison. relying on attempting to remember a snippet of sound. My (and others) rely on long passages, and NOT so much on memory of the actual sound, but on how the sound made you feel. That feeling is easy to remember. And if it is repeated, the collected feelings of each product with the different music can give one a clear preference, which will last when actually owning the product.
One will remember some of the highlights of the sound, but the meat of the comparison is the emotional response.

An additional thought:
we judge with the thinking side of our brain. We enjoy with the feeling side. (yes this is simplistic, but forgive me)
When we are auditioning, and just using the thinking side, we skip the part of our mind which will be the part that enjoys or dislikes the sound, in the long run.
So by including the feeling side in the process of auditioning, we can fufill the need of our whole mind.
The feeling side needs time to form it's 'opinions' the feelings. Then WITH the feelings included in our decision, we will be happier with our choices.

The OP asked a simple question. The answer pink noise and a db meter.
He/she is not asking whether one should be analytic or emotional regarding component comparisons or what the requisite period of time for a valid comparison.

The OP asked a simple question. The answer pink noise and a db meter.
He/she is not asking whether one should be analytic or emotional regarding component comparisons or what the requisite period of time for a valid comparison.

And (s)he was answered, and it turned into a more interesting discussion. The direction of the discussion is entirely pertinent to the direction of his question. What's the problem?

You cannot level match, unless you are picking a specific frequency, typically 1000 HZ. Music is not so simple. I use a verity of equalizations which are stored in memory and the perceived level changes with each one. Therefore, I agree that long term listening is essential to "evaluate them correctly", which was in fact the original posters declared goal.