Hello Inna,
The deterioration of sound (oxidation) is a very slow gradual occurrence. You will not notice it happening from day to day.
I will gaurantee that if you do clean them just once you will be convinced.
Oxidation on the cable connectors and the connectors on your equipment will gradually effect the sound.
A quick method to try, just once would be to get some de-natured alcohol, some paper towels and some pipe cleaners.
Disconnect your cables and wet the paper towel, not a lot, with the de-natured alcohol. Wipe the connectors down, you should see a black residue, wipe till clean, let dry. Dip the pipe cleaner in the de-natured alcohol, not a lot, to get the pins on the RCA connectors and the sockets on the equipment.
Put on your favorite music, something you are very familiar with.
Another quick method not as good is to just disconnect the cables from the equipment a few times, this will break up some of the oxidation.
I hope you try this just once if not and you are happy that is all that matters.
Respectfully,
Joe Nies
