Harmonics are additional tones created at frequencies beyond the fundamental tone. For example a fundamental tone of 250Hz would produce a harmonic at 500Hz, 750Hz, 1000Hz, 1250Hz etc. Lower order harmonics are less audible because they are consonant (harmonic), closer in pitch and more easily masked by the fundamental tone and are more easily tolerated. Higher and very high order harmonics are much more prominent at lower levels.