There are 8 sound effects (№0-№7) that can be interpreted either as a custom instrument or a custom waveform. Where in memory does a pico-8 cart store information about what sfx is in waveform-mode? Im guessing there's a byte somewhere in memory with each of its bits corresponding to each SFX mode. The question is - what's the address?

Update: figured it out.
You can check if a given SFX is a waveform instrument or not by checking if bit 7 at address 0x3242 + sfx_no*68 is set. Like this:

local sfx_id=2
local sfx_2_is_wave=@(0x3242+68*sfx_id)&128>0

If it is, you can also see if it's a BASS waveform by checking if bit 1 at address 0x3241 + sfx_no*68 is set. Like this:

local sfx_id=3
local sfx_3_is_bass=@(0x3241+68*sfx_id)&1>0