Explaining Sound: What is total harmonic distortion (THD)

We answer the question is what is THD and how does it affect sound quality in your headphone amplifier.

What is Total Harmonic Distortion?

Distortion is one of the biggest factors when it comes to producing the best sound possible. Distortion of a sound is exactly what it sounds like it is it is something extra being put into the final output signal and making it sound wrong ie distorted from its pure form.  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.

In your audio setup you are going to find total harmonic distortion in the amplification components whether it be in a pre-amplifier or amplifier section.  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 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.  

When looking at manufacturer specifications or frequency graphs relating to the amplification section of a particular piece of audio equipment you will commonly see THD listed as a %.  The lower the percent the better and 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.

Is Total Harmonic Distortion actually important?

To most people who enjoy listening to music the level of total harmonic distortion is most likely one of the last things to matter.  Why is this?  Well, THD levels are so good on most amps nowadays that they are virtually non existent to the human ear.  You see distortion comes in at almost every stage of the audiophile hobby.  There can be distortion due to poor mastering, file compression, headphone resonance, room reverberation etc.  There are lots of factors that can work against creating a truly pure audio signal and THD is just one of them.

So I don't need to worry about THD?

For the most part I would say no you don't need to worry about total harmonic distortion as most audiophile components already pay close attention to its minimisation beyond the realms of human hearing, but thats not the point.  You see audiophiles play a game of inches.  It is about minimising as many points of distortion in the hope of the final result yielding noticeable improvements.  There are numerous benefits to be had from refining other areas of your audio setup first but it can't hurt to keep an eye on THD and make sure it is as low as possible.