For some users, when pressing the voice chat key in Garry's Mod, the game may freeze. Here's how to fix it.
Step 1. Go to your control panel.
Windows 8, 8.1 and 10: Right click on the start menu button and select Control Panel.
Windows XP and 7: Open your Start menu and open the Control Panel.
Step 2. Open your microphone settings.
In your control panel, open the Sound category and go to the Recording tab.
Select your active recording device and open it's properties. The active recording device will usually have a sould level meter next to it.
Go to the Advanced tab and and make sure the checkboxes in Exclusive Mode are both not cheched.
After making the changes, press OK on the window and restart your PC.
Your voice chat should no longer causes freezes.