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OVERVIEW

    EEF stands for "Echo Envelope Format" and it's the format in which PSG
    instruments are stored.

FORMAT

    EEF instruments consist of a list of volume levels. Each byte represents
    a different volume level, and the value ranges from $00 (loudest) to $0F
    (quietest). Each byte represents one tick (i.e. 1/60th of a second).
    
    Looping is possible. The start of the loop is marked by a byte with value
    $FE, while the end of the loop is marked by a byte with value $FF. There
    must be at least one volume byte between them or Echo will hang.
    
    To make a non-looping PSG instrument, just put the last volume value
    inside the loop.

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NOTES

    Yes, this format was kind of an afterthought. Later I may improve it to
    provide at least some kind of RLE-like compression, but for now you'll
    have to stick with this :P
    
    Also, since PSG instruments are required to use PSG channels and I know
    many of you don't want to mess with them at all, here's a flat PSG
    instrument (i.e. no envelope):
    
        $FE,$00,$FF

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