Hi Zuki
This is probably the best there is, http://www.celemony.com/cms/index.php?id=products_editor and it works polyphonically too. (Just remember it is not a real time process)
Hope this helps

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).