downgrading a package

[SiKing]

Hi all.
A week ago I upgraded my system with all the level 3 updates and immediately afterwards music on my system works weird: seems like the mid-range is totally clipped. I am almost certain the problem is with the libavcodec53. Anyway, my problem is:
I went into synaptic and tried to force the previous version of this package. When I do that synaptic tells me that it will have to uninstall a whole bunch of stuff, including all my media players, plus it will have to install several packages that I obviously did not have previously. This does not seem like a safe procedure. Am I missing something? How do I safely downgrade a package to a previous version that I obviously had before without messing up the rest of my system?
TIA for any info.