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The total harmonic distortion (THD or THDi) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. Distortion factor, a closely related term, is sometimes used as a synonym.
Total harmonic distortion, or THD is a common measurement of the level of harmonic distortion present in power systems. THD can be related to either current harmonics or voltage harmonics, and it is defined as the ratio of the RMS value of all harmonics to the RMS value of the fundamental component times 100%; the DC component is neglected.
The relative contribution of harmonics to the distortion of the ideal waveform is called total harmonic distortion (THD). Low harmonic content in a waveform is ideal because harmonics can cause vibrations, buzzing, equipment distortions, and losses and overheating in transformers. Each of these power quality problems has a different cause. Some ...
Harmonic distortion results from nonlinear transfer curves. And once an amplifier's maximum amplitude is reached, signals will be clipped, resulting in even stronger harmonic distortion. Nonlinearity may be caused by heat due to power dissipation. Also, a transistor's operating point may move with temperature.
If there is any non-linearity in the device, this will cause harmonic distortion at the output. This kind of distortion consists of whole-number multiples of the applied signal frequency, as well as the original frequency being present at the device output. Intermodulation distortion can produce outputs at other frequencies.
A total harmonic distortion analyzer calculates the total harmonic content of a sinewave with some distortion, expressed as total harmonic distortion (THD). A typical application is to determine the THD of an amplifier by using a very-low-distortion sinewave input and examining the output.
Noise is also typically distinguished from distortion, which is an unwanted systematic alteration of the signal waveform by the communication equipment, for example in signal-to-noise and distortion ratio (SINAD) and total harmonic distortion plus noise (THD+N) measures.
Electrostatic speakers can have lower harmonic distortion but suffer higher intermodulation distortion. 3% distortion residue corresponds to 1 or 2% total harmonic distortion. Professional monitors may maintain modest distortion up to around 110 dB SPL at 1 m, but almost all domestic speaker systems distort badly above 100 dB SPL.