Sound fx data are initialised by init_sound_fx with data from sound_fx_data_table

Byte	Purpose
$00	Channel, $00 for tone/noise else mute
$01	Unknown, $00, $DC, $40
$02	Unknown, initialized to 0
$03	Frequency LSB
$04	Bits 4-7 attenuation, bits 0-3 frequency 2 MSbits or noise value
$05	Bits 0-3 command index, bit 7 must be set or channel is skipped
$06	Unknown, $00, $40, $80, $C0, $F0
$07	Unknown, $00, $01, $03