hmm... I mentioned in the "most influential person EVER in music" thread that on April 9, 1860 a man by the name of Edouard-Leon Scott de Martinville invented a device called the phonautograph and produced the earliest recording ever of a person singing. This would be the most important moment in music production history. For music history in general, I'm gonna have to go with Jackhammers train of thought and say the first person to discover how music could be made with the human body and/or some other device.