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OVERVIEW

    EIF stands for "Echo Instrument Format" and it's the format in which FM
    instruments are stored.

FORMAT

    EIF instruments are essentially raw dumps of the YM2612 registers. They
    consist of 29 bytes, where each byte belongs to a different YM2612
    register. The registers are stored in the following order (assuming the
    first FM channel):
    
        $B4                     -- Algorithm and feedback
        $30, $34, $38, $3C      -- Multiplier and detune
        $40, $44, $48, $4C      -- Total level
        $50, $54, $58, $5C      -- Attack rate
        $60, $64, $68, $6C      -- Decay rate
        $70, $74, $78, $7C      -- Sustain rate
        $80, $84, $88, $8C      -- Release rate and sustain level
        $90, $94, $98, $9C      -- SSG-EG
    
    Some bits are unused and ignored by the YM2612. In an EIF instrument,
    they *must* be 0, since Echo will rely on this for optimization purposes.

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