A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental frequency, therefore the sum of harmonics is also periodic at that frequency. Harmonic frequencies are equally spaced by the width of the fundamental frequency and can be found by repeatedly adding that frequency. For example, if the fundamental frequency is 25 Hz, the frequencies of the harmonics are: 50 Hz, 75 Hz, 100 Hz etc.

Many oscillators, including the human voice, a bowed violin string, or a Cepheid variable star, are more or less periodic, and so composed of harmonics.

Most passive oscillators, such as a plucked guitar string or a struck drum head or struck bell, naturally oscillate at not one, but several frequencies known as partials. When the oscillator is long and thin, such as a guitar string, or the column of air in a trumpet, many of the partials are integer multiples of the fundamental frequency; these are called harmonics. Sounds made by long, thin oscillators are for the most part arranged harmonically, and these sounds are generally considered to be musically pleasing. Partials whose frequencies are not integer multiples of the fundamental are referred to as inharmonic. Instruments such as cymbals, pianos, and strings plucked pizzicato create inharmonic sounds.

Lee Oskar (born March 24, 1948, Copenhagen, Denmark) is a Danish harmonica player, notable for his contributions to the sound of the rock-funk fusion group War, which he formed with Eric Burdon, his solo work, and as a harmonica manufacturer. He currently plays with Lowriderband, with Harold Brown, Howard Scott and B.B.Dickerson

Born in Copenhagen, Denmark in 1948, Oskar was six years old when a family friend gave him his first harmonica. "I came from an area where every kid on the block had a harmonica," he remembers. He grew up listening to Danish radio, enjoying all types of music and cites Ray Charles as the biggest influence from that period. When he was 17, Oskar decided that the United States was where a harmonica player should make his career, so he moved to New York at the age of 18 with little more than a harmonica in his pocket. With no money, Oskar played harmonica in the streets of New York. Eventually arriving in Los Angeles, California, via Toronto and San Francisco, Oskar soon met and joined forces with Eric Burdon who had recently disbanded The Animals and was searching for new collaborators. Together, the harp-playing Dane (born Oskar Levetin Hansen) and the British blues-rock singer made the rounds of the L.A. clubs, eventually hooking up with the soon-to-be members of War. Burdon agreed to the novel idea of pairing up Oskar's harmonica with Charles Miller's saxophone to form a horn section. This team-up set War apart from the start, giving Oskar room to display the full spectrum of his improvisational prowess. Oskar's harmonica magic was always a vital element in War's music and performances. Oskar continued with War for 24 years non-stop. At the end of 1992 he made the decision to end his association with that group in order to have the time to pursue his solo career.