I’ve recently talked about what is aliasing and why it causes an unwanted distortion. Let’s talk about oversampling and when and why you should be using it when it’s an option.
What is Oversampling in Audio
Oversampling in audio refers to applying a higher sample rate than you have natively set. Many modern plugins have an oversampling feature to increase the sample rate to the audio they’re processing.
Why does this exist?
Let’s use a common example where oversampling is helpful. Let’s say we’re dropping an exciter plugin on a vocal.
An exciter is essentially a saturation plugin which adds overtones, or higher frequency information to tracks where it wasn’t present before.
Exciters are commonly used in the mastering stage, but can be applied to any track which you feel could benefit from some enhanced high mid and high frequencies. Oftentimes it’s a useful fix for tracks which are too low or mid heavy or even muddy.
Adding higher frequency information as an alternative to trying via EQ to boost what’s not there oftentimes works better.
Regardless, an unintended consequence of this sometimes is that these overtones can go beyond the range of what our sample rate can reproduce.
As I mentioned in my overview on sample rate, in the digital realm, our frequency ceiling is actually HALF of our set sample rate.
So if our sample rate is say 44,100Hz, this means the highest frequency we can reproduce in our DAW is 22,050Hz.
Our vocal exciter can easy create overtones which surpass 22k, causing foldover distortion back in the audible frequency range called aliasing.
THIS is why oversampling exists. This pushes the sample rate within the plugin to 88k, 96k, etc. to the point that the ceiling is so high that aliasing can’t exist.
The plugin adds an anti-aliasing filter before the audio is passed to the next plugin in the chain, removing any frequencies above your native sample rate.
Why You Shouldn’t Use Oversampling
You might be wondering why you wouldn’t want to use oversampling if it prevents aliasing.
The only instance in which you wouldn’t want to use oversampling is if aliasing isn’t an issue. Oversampling, just like raising your native sample rate, is harder on your CPU.
Plugins add up quickly in taxing your processor; running oversampling in many or all of your plugins which allow for it can make playback, let alone mixing, difficult to next to impossible.
There are other ways to deal with aliasing besides oversampling, so refer back to tutorial on how to avoid aliasing to ensure this isn’t a problem in your mix.
So to sum up, oversampling is a feature on many modern plugins which increases the sample rate to accommodate for any new high frequencies the plugin adds through its processing.
Sometimes enabled by default, sometimes a specific setting you need to turn on to use it, this ensures that there’s no aliasing producing foldover in your audio.
The plugin will then apply an anti-aliasing filter to filter out these ultra high frequencies for when the sample rate returns to the native setting when the audio is output from that plugin.
Using oversampling is typically a good option when it’s available to ensure aliasing is not an issue with that track, and oftentimes it’s just a passive setting so you don’t even need to worry about turning it on or off.