Spend some time shopping for audio products, whether it’s a Bluetooth speaker or an audiophile headphone amp, and you’ll find out about distortion. But what is audio distortion and where does it come from in the first place?
What is audio distortion?
It doesn’t help that the definition of distortion is terribly vague, even if you limit it to just audio distortion. If an audio waveform outputs a given signal shifted or warped compared to the input signal, that’s technically distortion.
There are two types of audio distortion: linear and nonlinear. Linear distortion is a change in the amplitude of a signal, while nonlinear distortion is a change in the frequency content of a signal. While both are forms of audio distortion, when most people talk about audible distortion, they mean non-linear distortion.
Linear distortion adds nothing to a signal. Instead, it changes it directly. This can be in very noticeable ways, such as changing the pitch or volume of a sound, or in more subtle ways, such as altering the phase of a signal.
Nonlinear distortion adds extra frequencies to the signal. These can sound like a grainy texture over the sound, almost like you’re listening to an old vinyl record. You can add a buzz, hiss, or crackle to your recordings.
That said, nonlinear distortion isn’t always unpleasant. Most pop music production uses various forms of nonlinear distortion throughout the mixing process, even on what sound like pristine, clean recordings.
In this article, we’re focusing on the nasty side of audio distortion with the three most common forms you’re likely to encounter. These are total harmonic distortion, clipping, and speaker distortion.
Total Harmonic Distortion (THD)
Harmonic distortion is sounds that have been added to the original frequencies present in a signal. Total harmonic distortion is a measure of how much of an audio signal consists of those newly added harmonic frequencies compared to the original.
Harmonic frequencies are not always undesirable. If music were all fundamental frequencies, it would be pretty boring. The harmonics in sound are what give instruments their unique timbres. The low E string on a guitar is about 83 Hz, but the harmonics at different frequencies are what give it the sound of a guitar string.
This is not all that harmonics are useful for. As an example, audio engineers often enhance the harmonic frequencies around bass instruments to ensure you can hear them on smaller speakers that can’t physically reproduce the fundamental frequency.
When components in your stereo system add harmonics to a signal, they’re usually not pretty. This is why manufacturers try to keep the total harmonic distortion of their components as low as possible. The THD of a class D amplifier, for example, is often well below one percent.
There’s a reason for this one percent figure: that’s the level at which people will start to notice. While only a few people can hear distortion well below one percent, most will notice when it goes above that figure.
Harmonic distortion is present in any product that includes an amplification stage, from your telephone to your home theater system. Fortunately, you won’t hear it often and you don’t need to worry about it.
Clipping is what happens when a signal exceeds a specific threshold. This threshold is often the power rating of an amplifier, but clipping can occur in an audio signal at many different stages for a variety of reasons.
No matter how or why the signal exceeds the threshold, this effectively cuts off the peaks of the signal. Where in a signal chain the clipping occurs will determine how quickly it occurs, meaning clipping can range from barely noticeable distortion to a loud, jagged sound that makes you rush to press the button. stereo power on.
Digital cropping is usually the nastier variety. This can happen in software, in a component’s analog-to-digital (ADC) or digital-to-analog (DAC) converters, or in a stand-alone product like an external DAC. No matter what, it’s not something you want to hear.
Of course, how nasty clipping sounds is often a result of how you use it, and in the analog world it can sound great. Guitar distortion and overdrive are forms of clipping, allowing a guitar to sing in a way that it couldn’t otherwise.
That said, when clipping occurs in your stereo system, due to a component mismatch or simply turning the volume up too high, it’s never a good thing.
Speaker distortion is exactly what it sounds like, and it sounds like your speaker is trying to break down.
The good news is that more often than not, what you’re hearing as a distorted speaker may actually just be clipping. This is probably your amp struggling to drive the speaker and getting distorted as it is exceeding its maximum power rating to try to get sound to the speaker. Turn down the volume and this will stop.
Other times, what you’re hearing is non-linear motion in the speaker driver, which should be moving linearly. This can be the result of using an amplifier that is too powerful, or an ohm mismatch between the speaker and the amplifier.
In a loudspeaker, when the electrical signal hits the driver’s voice coil, the driver must move with the waveform. If the audio signal is too powerful, the movement can start to bottom out at the ends, meaning it can’t push any more air. This is where you start to hear the actual distortion from the speaker.
If this continues, this can physically damage the speaker, so if you think you’re hearing distortion from the speakers, make sure you turn the volume down as quickly as possible. Even if it turns out that there is clipping, this usually means that something is wrong with your stereo or home theater system.
To make sure everything is hooked up correctly, take a look at our guide to home theater wiring connections.