Ubuntu slows down when the laptop lid is closed, why?

Question

laptops

The same program for converting sound in realtime (mine) works fine with the laptop open, and if you close the lid, there are very often sound breaks (even if you turn off all processing and just copy the input signal to the output). Where to dig?

Answer 1

Connect to the closed laptop from another computer via SSH.
1) energy saving (already written). See the frequency in /proc/cpuinfo
2) parasitic processes. See the htop command.

Answer 2

Well, I dare say, you need to dig in the direction of the action of the laptop when closing the lid.
Now I've looked - energy saving options - power management - with the lid closed - and in 2 options it is affixed - Idle.
The laptop works all night, with the lid closed, so far there are no comments
PS: OS - Linux Mint
I think it is not much different from ubuntu