The Casio CTK-720 is a legacy synthesizer manufactured by Casio until the early 2000s. Although outdated, some CTK-720s are still available for sale new in the box at a few locations. Primarily intended for use as a stand-alone synthesizer, Casio included basic MIDI functionality that makes it possible to use the CTK-720 as a MIDI controller. Getting the CTK-720's MIDI functions to work on today's computers requires that a generic USB-to-MIDI driver, provided by Casio, be installed on your system.
Download and install the general USB-MIDI Driver from Casio's website. This driver is compatible with all versions of Windows up to the 32-bit version of Windows 7. Follow the instructions included with the download.
Turn the CTK-720 off. This is usually good practice when making any kind of connection between different elements.
Connect one end of the USB cable to the USB port on the back panel of the CTK-720 and connect the other end to an available USB port on your computer.
Turn the CTK-720 on. Its onboard software will initialize and display its default message.
Press the "Setting" button on the CTK-720 repeatedly until its screen reads "GM Mode."
Press the "+" button to switch the CTK-720 to General MIDI mode. The screen will read "on GM Mode."
Select a MIDI channel on which to send MIDI information from the CTK-720 by pressing the "Setting" button until the screen reads "Keybd Ch."
Press the "+" or "-" button to increase or decrease the MIDI channel number. For basic usage, MIDI channel 1 will suffice.
Open the software MIDI synthesizer, sequencer or other MIDI-enabled application of your choice on your computer. You may need to establish an input device in the application's preferences in order for it to receive MIDI transmissions from the CTK-720. Consult the application's documentation for details. The CTK-720 will most likely appear as "USB-MIDI" or some derivation thereof in the list of available devices.
Play some notes on the CTK-720. You will hear the software instrument play back the notes you press. If you are using a sequencer, there will most likely be some indication somewhere in its interface to show that it is receiving MIDI data from the CTK-720.