Latency is the delay between a signal being sent (such as a MIDI note being triggered), and the resulting sound you hear. The effects of this may be apparent to you if you are using a virtual instrument for the first time, and it can be extremely frustrating, sometimes making even normal operation next to impossible.

So Just What is Latency?

If you were talking to someone right next to you, the time it takes the sound to go from your mouth to their ear would be, for the most part, instantaneous. Now if that person is on the other side of a football field, the sound would have to travel 100 yards from your mouth to their ear before they could hear you. That's about 300 milliseconds (sound travels about 1 Foot/ms)!

That's fine for outdoors, but what about in a computer?

In a computer, latency is caused by the amount of time it takes your computer to process the incoming signal (like our MIDI note), act accordingly (tell the plug-in to play the sound), and output the result (have the sound come out of your audio interface). The two main culprits in determining latency are your audio interface, and your computer's performance.

Your Audio Interface

There are settings for any high-quality audio interface that will allow you to reduce the latency by adjusting the buffer (momentary storage for the audio). However, lowering the latency (buffer setting) will usually be done at the expense of system resources. Not having the right drivers selected in the audio panel for the plug-in itself (if in stand alone mode), or in the settings for the host program that the plug-in has been opened in, will also cause high latency. The ASIO drivers supplied with a good audio interface are the ideal ones to use in order to help keep your sanity when using plug-ins. A reasonable amount of latency that will allow you to record midi notes from a keyboard or controller accurately, while hearing the audio output from the virtual instrument, is probably somewhere below 20ms (although this may vary as a matter of taste).

Your CPU