You’ll still have to multiply your audio with the envelope track using something like this Nyquist code …
(sim (mult (aref s 1) -0.5)
(mult (sum 0.5 (scale 0.5 (aref s 0)))(aref s 1)))
https://forum.audacityteam.org/t/how-can-i-amplitude-modulate-one-channel-with-another/8039/5
(I think 
)