In: A=Envelope number (1..15), HL=Pointer to Data (must be >3FFFh)
The data block starts with a header byte:
bit7bit6-0 number of following 3-byte parameters (1..5)
The following 3-byte parameters can be (when Byte 0, Bit7=0):
Byte 0 Number of steps (01h..7Fh)