Hot content algorithm / score with time decay
===

I have been reading + researching on algorithms and formulas to work out a score for my user submitted content to display currently hot / trending items higher up the list, however i'll admit i'm a little over my head here.

I'll give some background on what i'm after... users upload audio to my site, audios have several actions:

 - Played
 - Downloaded
 - Liked
 - Favorited

Ideally i want an algorithm where I can update an audios score each time a new activity is logged (played, download etc...), also a download action is worth more than a play, like more than a download and a favourite more than a like.

If possible i would like for audios older than 1 week to drop off quite sharply from the list to give newer content more of a chance of trending.

I have read about reddits algorithm which looked good, but i'm in over my head on how to tweak it to make use of my multiple variables, and to drop off older articles after around 7 days.

Some articles that we're interesting:

 - http://amix.dk/blog/post/19588 (reddits algo)
 - http://www.evanmiller.org/rank-hotness-with-newtons-law-of-cooling.html

Any help is appreciated!

Paul