Many factors can work against creating a truly pure audio signal, and THD is just one of them. There can be distortion due to poor mastering, file compression, headphone resonance, room reverberation, etc. You see, distortion comes in at almost every stage of the audiophile hobby. Why is this? Well, THD levels are so good on most amps nowadays that they are virtually nonexistent to the human ear. To most people who enjoy listening to music, the level of total harmonic distortion is most likely one of the last things to matter. Is Total Harmonic Distortion actually important? In an ideal situation for use with headphones, speakers, and earphones, you would be looking for a total harmonic distortion level as close to zero as possible. When looking at manufacturer specifications or frequency graphs relating to the amplification section of a particular audio equipment piece, you will commonly see THD listed as a %. In this regard, we can consider that the lower the THD figure, the better the sound quality, as this would mean the audio signal is in a purer form.
In the simplest form, THD is a value of measurement given to the difference between the input signal and the output signal from the amplifier. In your audio setup, you will find total harmonic distortion in the amplification components, whether in a pre-amplifier or amplifier section. Audiophiles work hard at all stages of their setup, whether it be with headphones and earphones right up to full-blown audiophile-grade HiFi systems, to reduce distortion to the sound signal wherever possible, and today we are going to look at the effect of Total Harmonic Distortion or THD as it is commonly represented. It is extra being put into the final output signal and making it sound wrong, i.e., distorted from its pure form.
Distortion of a sound is exactly what it sounds like. THD is a measure of that additional signal content not present in the input signal.Distortion is one of the biggest factors when it comes to producing the best sound possible. When a sinusoidal signal of frequency ω passes through a non-ideal, non-linear device, additional content is added at multiples nω (harmonics) of the original frequency. 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. IEEE std 519-2014 covers the recommended practice and requirements for harmonic control in electric power systems. In power systems, lower THD implies lower peak currents, less heating, lower electromagnetic emissions, and less core loss in motors. Since harmonic distortion tends to 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 radio communications, devices with lower THD tend to produce less unintentional interference with other electronic devices. In audio systems, lower distortion means the components in a loudspeaker, amplifier or microphone or other equipment produce a more accurate reproduction of an audio recording. Distortion factor, a closely related term, is sometimes used as a synonym.
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 produced by an amplifier, as measured in terms of the harmonics of the sinusoidal components of the signal that it introduces
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