If it was the middle of the day, I definitely would not call the police. If it's been going all day and then extends into late night (midnight or later), I might call, but even then, I'd hesitate, especially if the neighbors were not typically loud.
If I were the one having the party at my house, and the police came by and said that a neighbor had called to complain about the noise, then I think I'd turn down the music (even if it's during the daytime). I don't want to deliberately disturb my neighbors.