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Total harmonic distortion
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.
In audio systems, lower distortion means that the components in a loudspeaker, amplifier or microphone or other equipment produce a more accurate reproduction of an audio recording.
In radio communications, devices with lower THD tend to produce less unintentional interference with other electronic devices. Since harmonic distortion can potentially widen the frequency spectrum of the output emissions from a device by adding signals at multiples of the input frequency, devices with high THD are less suitable in applications such as spectrum sharing and spectrum sensing.
In power systems, lower THD implies lower peak currents, less heating, lower electromagnetic emissions, and less core loss in motors. It is a key metric in the stability and quality of the U.S. electrical grid. IEEE Standard 519-2022 covers the recommended practice and requirements for harmonic control in electric power systems.
To understand a system with an input and an output, such as an audio amplifier, we start with an ideal system where the transfer function is linear and time-invariant. When a sinusoidal signal of frequency ω passes through a non-ideal, non-linear device, additional content is added at integer multiples nω (harmonics) of the original frequency. THD is a measure of that additional signal content not present in the input signal.
When the main performance criterion is the "purity" of the original sine wave (in other words, the contribution of the original frequency with respect to its harmonics), the measurement is most commonly defined as the ratio of the RMS amplitude of a set of higher harmonic frequencies to the RMS amplitude of the first harmonic, or fundamental frequency
where Vn is the RMS value of the nth harmonic voltage, and V1 is the RMS value of the fundamental component.
In practice, the THDF is commonly used in audio distortion specifications (percentage THD); however, THD is a non-standardized specification, and the results between manufacturers are not easily comparable. Since individual harmonic amplitudes are measured, it is required that the manufacturer disclose the test signal frequency range, level and gain conditions, and number of measurements taken. It is possible to measure the full 20 Hz–20 kHz range using a sweep (though distortion for a fundamental above 10 kHz is inaudible).
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Total harmonic distortion AI simulator
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Total harmonic distortion
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.
In audio systems, lower distortion means that the components in a loudspeaker, amplifier or microphone or other equipment produce a more accurate reproduction of an audio recording.
In radio communications, devices with lower THD tend to produce less unintentional interference with other electronic devices. Since harmonic distortion can potentially widen the frequency spectrum of the output emissions from a device by adding signals at multiples of the input frequency, devices with high THD are less suitable in applications such as spectrum sharing and spectrum sensing.
In power systems, lower THD implies lower peak currents, less heating, lower electromagnetic emissions, and less core loss in motors. It is a key metric in the stability and quality of the U.S. electrical grid. IEEE Standard 519-2022 covers the recommended practice and requirements for harmonic control in electric power systems.
To understand a system with an input and an output, such as an audio amplifier, we start with an ideal system where the transfer function is linear and time-invariant. When a sinusoidal signal of frequency ω passes through a non-ideal, non-linear device, additional content is added at integer multiples nω (harmonics) of the original frequency. THD is a measure of that additional signal content not present in the input signal.
When the main performance criterion is the "purity" of the original sine wave (in other words, the contribution of the original frequency with respect to its harmonics), the measurement is most commonly defined as the ratio of the RMS amplitude of a set of higher harmonic frequencies to the RMS amplitude of the first harmonic, or fundamental frequency
where Vn is the RMS value of the nth harmonic voltage, and V1 is the RMS value of the fundamental component.
In practice, the THDF is commonly used in audio distortion specifications (percentage THD); however, THD is a non-standardized specification, and the results between manufacturers are not easily comparable. Since individual harmonic amplitudes are measured, it is required that the manufacturer disclose the test signal frequency range, level and gain conditions, and number of measurements taken. It is possible to measure the full 20 Hz–20 kHz range using a sweep (though distortion for a fundamental above 10 kHz is inaudible).