Harmonics are primarily generated manually, using a variety of techniques such as the pinch harmonic. Frequency multipliers use circuits tuned to a harmonic of the input frequency. Musical intervals are complementary values of the harmonic overtones series. Materials capable of generating a second harmonic are crystals without inversion symmetry. Guajeos are a seamless blend of European harmonic and African rhythmic structures. There was also a distinction between melodic and harmonic dissonance. Tuned mass dampers stabilize against violent motion caused by harmonic vibration. In China, the guqin has a musical scale based on harmonic overtone positions. The result is near complete absence of harmonic distortion. These are known as quantum harmonic oscillators. This is the form of a classic harmonic oscillator. FM synthesis can create both harmonic and inharmonic sounds. A consequence is that can be obtained from the functional determinant of the harmonic oscillator. This is the Hamiltonian for an infinite number of uncoupled harmonic oscillators. Interpolation of periodic functions by harmonic functions is accomplished by Fourier transform.