When I press the keys I don't immediately hear the notes - there is a lag, what's going on?
This problem is called latency. It occurs when a computer is either not powerful enough to process the audio events in real time, or the computer requires a reconfiguration of the audio drivers and settings. This article provides tips and possible remedies. We've also made an easy-to-follow video.
Mac vs Windows: If you have a Mac available to you, make the switch. Macs all come out of the same factory and have quite competent sound cards/drivers. You shouldn’t experience latency even when going directly out of the headphone jack. Windows machines are made by everyone and while some have excellent hardware and sound drivers that won’t exhibit any latency, others undoubtedly will.
If you need to use a Windows machine, see if you have (or can buy/borrow) an Audio Interface; i.e. an external sound card. In short, this external device connects to your computer via USB and sound is routed through it. We link to a number of brands we trust here.
If you need to use a Windows machine and do not have an audio interface, you can try Exclusive Mode (video).