mpg123 -- equalizer ?

Press RESET immediately, All! The mpg123 program has the following option: -E f Equalizer, data from file. But nowhere, neither in the mana nor in any other documentation, is it described what should be in this file and why it is needed at all. :-( Maybe someone knows? I want low frequencies strengthen it a little (xmms I don’t need it, it plays crookedly).