QUOTE(kotrtim)
really?....cool I don't even know there is such a thing.
It's somewhat shocking that there's anyone out there who hasn't heard of this. Backmasking has a long and storied tradition in Rock and Roll. A few songs have intentional backwards messages, but most are accidental, and "back in the day" was enough to have a bunch of wackos try to ban your recrod for corrupting the youth. Part of "Stairway to Heaven" famously sounds like "my sweet satan" backwards (and a longer phrase if you listen very carefully). Actually, for some reason, lots of English words/phrases sound like "satan" when played backwards.
This page has a bunch of good examples of all sorts of backwards messages in music. The AC/DC "Dirty Deeds" and Queen "Another One Bites the Dust" ones are the best IMO.
They Might Be Giants has a number of songs with backwards recorded stuff in them. IIRC one is just a reverse of them babbling in gibberish. They also have a way of singing in a few songs that sounds like it's a backwards recording but isn't. The song "On Earth My Nina" is a regular, (mostly) intelligible recording (sung strangely) that is meant to sound what another, more ordinary song "Thunderbird" sounds like when played backwards. The phrase "on earth my nina" is what "I remember now" sounds like in reverse. "On Earth My Nina" was actually released on their internet-only album "Long Tall Weekend" years before they even started performing "Thunderbird" in concert (their most recent album, "The Spine", released a few months ago is the first "official" recording of "Thunderbird".)
"I'll Sink Manhattan" is another song from TMBG with backwards messages - in this case, a recording from the NYPD left on their dial-a-song answering machine. It isn't an answering machine anymore, but you can still get free music at 718-387-6962.
Interestingly, I accidentially discovered that the phrase "yeah right" sounds exactly the same forward and backwards, espescially if spoken with the doubtful tone in which that phrase is normally used. The way you said it right now when you read this is perfect. Seriously, this isn't one of those "gullible isn't in the dictionary" things. Anyhow, I don't know of any other phrases that sound the same backwards, but they probably exist. Sorta an "audio palindrome".
I'd imagine some kinds of mp3 artifacts might be more audible when played backwards, e.g. the post-masking effect after sharp attacks is stronger and has longer duration than the pre-masking effect. Because of that, a smart encoder would introduce more noise after an attack than before, and this might be detectable if you play it back in reverse.