Is there a way to disable USB 3.0 and enable legacy USB 2.0 support on Windows 8? I have an old microphone (Blue Snowflake) that only works when plugged into a USB 2.0 port. Is there any way to disable USB 3.0 support, either system-wide or specifically (to a USB drive or to a particular device), and fall back on the old USB 2.0 stack?
You should be able to disable USB 3.0 inside your BIOS screen.
Also, if this system is home-built, make certain to install the drivers that came with the motherboard (if you don't have the disk, just check the manufacturer's website), rather than just let Windows install the default drivers. Those could potentially cause an issue for you.
The USB 3.0 plug is significantly different from a USB 2.0 Plug.
If you look into the USB 3.0 Plug, on the back-end roof of the plug head, there are 5 extra data transfer pins. When the pins are engaged, USB 3.0 Protocol is activated.
Obviously the USB 2.0 lacks these extra pins, when it connects USB 2.0 is defaulted having no register of the 5 extra pins.
Your Blue Snowflake by all means should work with Windows 8(.1) on a USB 3.0 Hub.
Helpful diagrams can be found at this source (page 8): http://www.usb.org/developers/presentations/pres0410/1-2_SSUSB_DevCon_Arch_Overview_Dunstan.pdf
If the particular USB2 mike doesn't work in USB 3.0 port, there must be some deeper problem at system/driver level.
Technically, there is no need to disable USB 3.0 in order to get a USB2 device working. Electrically speaking, the legacy USB2 works in parallel with new USB3, over a separate set of legacy wires (D+, D-, sharing GND and VBUS with USB3). Therefore, when a USB2 device is plugged in, USB3 section will have no connect and no effect, and the communication should proceed over the legacy wires.
However, the USB3 ports are under control of a different controller, xHCI, which also supports USB2 operations, but with a new xHCI driver. If the software for the old proprietary USB2 device is written without regard for system driver-device application interface and somehow expects specific old controller (EHCI), the simple disabling the xHCI controller might be of no help.
BTW, disabling the USB3 functionality is as simple as going to Device Manager, and setting the eXtensible Host Controller (in USB section) to "disable".