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What is total harmonic distortion (THD)?

Total Harmonic Distortion, or THD, is a measure of the amount of distortion that occurs when an audio signal passes through a device. It’s measured in decibels and can be expressed as a percentage. The higher the number, the more distorted your sound will be.
The most common form of THD is found on power amplifiers where it’s often referred to as “power supply noise.” This refers to the unwanted electrical noise generated by the amplifier itself. Power supplies are designed with high-quality components which minimize this type of noise. However, if you’re using a cheap power supply, then you’ll experience some level of THD.
Power Supply Noise
Power supply noise is usually measured at the output of the amplifier and is typically in the range of -120 dBu to -130 dBu. If you’re not familiar with these numbers, they represent the difference between the cleanest signal possible and the worst case scenario. For example, if you have a 100dB signal coming into your amplifier, then you should expect about 90dB of clean signal out of the amplifier. Anything above 110dB would indicate that there was some level of noise present. In other words, anything below 110dB is considered to be clean.
If we take our 100dB signal and pass it through a power supply that has a THD of -120 dBu, then we’d get something like 95dB of clean signal. That means that 5dB of noise was added to the signal. Now let’s say that same signal is passed through a power supply with a THD of -130 dBu. We’d end up with only 85dB of clean signal. So, even though the power supply had a lower THD than the first one, it actually ended up adding more noise to the signal.
In general, the less expensive the power supply, the greater the chance for additional noise being introduced. You may also notice that cheaper power supplies tend to have a slightly higher THD.
How Does THD Affect Your Audio?
When you listen to music, you’re hearing the original waveform from the recording. When you play back that waveform, you’re introducing additional distortion due to the amplifier and speaker. Some of this distortion comes from the amplifier itself while others come from the speakers themselves.
For instance, if you were listening to a guitar solo, then you might hear some harmonics that weren’t originally present in the recording. These harmonics are created by the amplifier and speaker combination. They add coloration to the sound but aren’t necessarily bad. On the contrary, many people enjoy the extra character that these harmonics provide.
However, if you’re listening to a song that contains lots of bass, then you may find yourself getting fatigued after a few minutes because the low frequencies are so loud. This is because the amplifier is having to work harder to drive the speakers. As a result, the amplifier is producing more distortion.
What Can I Do About It?
There are several things that you can do to reduce the amount of THD that you encounter. First, make sure that you’re using a quality power supply. Second, try to use a good quality cable. Third, avoid using cheap speakers. Finally, don’t overload your system.
By following these tips, you’ll be able to improve the overall sound quality of your system without spending too much money.