Total Harmonic Distortion (THD) Calculator
Calculate total harmonic distortion (THD) from distortion attenuation in dB. Free online THD calculator for audio engineers and electronics enthusiasts with interactive charts.
About This Calculator
The Total Harmonic Distortion (THD) Calculator converts distortion attenuation in decibels (dB) to THD percentage using the standard formula. This tool is essential for audio engineers, electronics designers, sound system calibrators, and anyone working with signal quality analysis in audio and power systems.
THD is calculated using the formula: THD (%) = 10(ak / 20) × 100, where ak is the distortion attenuation in dB. The calculator also displays signal purity as the percentage of the signal that is free from harmonic distortion. Lower THD values indicate cleaner, more accurate signal reproduction.
Understanding THD in Audio Systems
Every signal processing component — amplifiers, speakers, microphones, DACs — adds some level of harmonic distortion. The THD factor compares input and output audio signals, with the difference measured as a percentage. A THD of 0.1% means 0.1% of the output signal contains unwanted distortion. High-fidelity systems aim for THD below 0.1% (-60 dB).
THD in Power Systems
In electrical power distribution, THD measures voltage or current waveform distortion caused by non-linear loads like rectifiers, variable frequency drives, and LED lighting. IEEE 519 standard recommends THD below 5% for general power systems to prevent equipment overheating and interference.
Frequently Asked Questions
What is total harmonic distortion (THD)?
Total harmonic distortion (THD) is a measurement of the harmonic distortion present in a signal. It is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency, expressed as a percentage. Lower THD means more accurate signal reproduction in audio systems.
How do you convert distortion attenuation to THD?
THD is calculated from distortion attenuation using the formula: THD (%) = 10^(ak / 20) × 100, where ak is the distortion attenuation in decibels (dB). For example, -40 dB attenuation corresponds to 1% THD, while -60 dB corresponds to 0.1% THD.
What is a good THD value for audio equipment?
For high-fidelity audio equipment, THD below 0.1% (-60 dB) is considered excellent, while THD below 0.01% (-80 dB) is exceptional. Consumer audio equipment typically has THD between 0.1% and 1%. The human ear can rarely perceive THD below 0.5% in practical listening tests.
How is THD measured in audio systems?
THD is measured by applying a pure sine wave to a system and analyzing the output for harmonics. A spectrum analyzer or audio analyzer captures the fundamental frequency and its harmonics. The RMS voltage of all harmonics is divided by the RMS voltage of the fundamental to compute the THD percentage.
What factors affect total harmonic distortion?
THD is affected by amplifier design, component quality, power supply stability, signal level, frequency response, and operating temperature. Nonlinearities in transistors, op-amps, and transformers introduce harmonics. Operating equipment within its designed power range typically minimizes THD.
Why is THD important in power systems?
In power systems, high THD can cause overheating of transformers and motors, nuisance tripping of circuit breakers, and interference with sensitive electronic equipment. Power quality standards like IEEE 519 limit THD to below 5% for general distribution systems and below 3% for sensitive applications.