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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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