Refers to an audio source that is not directly in front of a transducer, especially a microphone. This results in off-axis coloration; a distortion or change in the frequency response of the reproduced audio signal. Often this coloration is put to good use. For example, many engineers intentionally set up mics on guitar amps so that they are slightly off access to control the amount of high frequencies captured. A microphone will generally produce the “truest” results if it is used on-axis (oriented directly in front of the sound source).