527
Here is the layout of a SoundBlaster patch (as
I suppose it to be):

offset:
 0-3: "SBI", 0x1a
 4-19: voice name
 20-28: unused
 29: echo delay
 30: echo attenuation
 31: chorus spread
 32: transpose
 33: fixed duration
 34: extra voice
 35: fixed key
 36,37: 0x24 (modulator) & 0x25 (carrier)
  b7: am vibrato
  b6: frequency vibrato
  b5: sustain
  b4: duration varies with frequency
  b3-b0: frequency multiplier
 38,39: 0x26 (modulator) & 0x27 (carrier)
  b7-b6: amplitude = frequency factor
  b5-b0: loudness
 40,41: 0x28 (modulator) & 0x29 (carrier)
  b7-b4: attack rate
  b3-b0: decay rate
 42,43: 0x2a (modulator) & 0x2b (carrier)
  b7-b4: sustain level
  b3-b0: release rate
 44,45: 0x2c (modulator) & 0x2d (carrier)
  b7-b2: unused
  b1-b0: modulator/carrier distortion
 46: 0x2e:
  b7-b4: unused
  b3-b1: phase shift by modulator
  b0: 1 = parallel (additive)
      0 = frequency modulation
 47-: 0x2f-... unused

The layout of an opl3 patch is similar, except that
bytes at offset 0-2 are "4OP", 47-48 are like the
bytes at 36-37 except they are for operators 3 and 4,
49-50 are like 38-39, 51-52 are like 40-41, 53-54 are
like 42-43, and 55-56 are like 44-45.  57 is like
46, except there is no phase shift for operator 3.
58-59 are unused.
53-54
			--gl
.

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