Welcome to sage audio. Today our topic is Oversampling Explained.
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What is Oversampling?
Oversampling is an increasingly common function in most plugins, which increases the sampling
rate of the signal it’s processing by a fixed multiple like 2 or 4. So if the sampling
rate of your session is 48kHz, a 2x oversampling setting will make the sampling rate 96kHz.
The process of oversampling can be CPU intensive, and can cause performance issues if too high
of a rate is used.
Simply put, oversampling increases the maximum frequency your processors can handle, and
increases the accuracy with which the signal is encoded and processed.
This makes it a great option for reducing distortion and subtly increasing the clarity
of your signal.
What does Oversampling Do?
Oversampling reduces or completely gets rid of 3 forms of potential distortion a signal
can have: aliasing, clipping, and quantization distortion. Although these forms of distortion
often are mild and difficult to consciously hear, they’re often noticed when using a
lot of processing or pushing a processor harder.
First, oversampling reduces aliasing distortion by allowing a processor a higher frequency
at which to process the signal.
Second, It reduces clipping distortion by making the signal's amplitude more accurately
encoded, which if the signal is close to 0dB, can be the difference between clipping and
not clipping.
And third, it reduces quantization distortion, or the difference between the actual signal
and the encoded signal.
When Should I Use Oversampling?
If you’re using a lower sampling rate for your session, but you still want to use a
fair deal of processing, it helps to use oversampling to reduce distortion. Oversampling should
be used both in mixing and mastering sessions, when either aggressive or a lot of processing
is being used.
For example, oversampling causes more accurate encoding and quantization of the signal’s
amplitude - so if you’re using a limiter, and you’re pushing the signal up to 0dB,
use oversampling to make the signal encoded more accurately.
This may cause a peak that clipped to actually not clip, in turn reducing clipping distortion.
What is Aliasing Distortion?
Aliasing distortion occurs when the signal fed into a processor has exceeded the maximum
frequency that that processor can handle or accurately represent as determined by the
sampling rate. When it does occur, harmonics are reflected down the frequency spectrum,
which causes both unpleasant harmonic and phase distortion.
For example, say my sampling rate is 48kHz. Using the Nyquist theorem we know that the
maximum frequency which can be represented is 24kHz. So if the signal goes above this,
say to 32kHz, we’ve gone above this by 8000Hz.
If we reflect this value back down the spectrum, we know our distortion will be 8kHz less than
24kHz.
Do I Need to Worry About Aliasing Distortion?
You’re probably wondering if you even need to be concerned about aliasing distortion,
considering most signals only go up to 20kHz, and a 44.1kHz sampling rate covers that frequency;
however it may still be an issue. If you’re processing higher frequencies with distortion
plugins, you’ll likely cause aliasing distortion.
Say you’re distorting your high-frequency range, and your distortion starts at 15kHz.
Now, let’s say this distortion causes a 2nd order harmonic.
This harmonic will be at 30kHz, far above the range that can be handled by our sampling
rate - resulting in aliasing.
Oversampling and Analog Emulation
If you want to more accurately emulate analog equipment, you’ll most likely need to use
oversampling to reduce aliasing. Although aliasing is subtle, it can add up amongst
multiple signals and processors, resulting in a distinctly digital sound, often characterized
as sounding metallic or brittle.
If you’re using a form of analog emulation, check to see if oversampling is an option
- it’ll greatly reduce the impact of aliasing, and result in a less-digital sound.
This is why a lot of developers, especially analog emulation developers, are beginning
emphasize oversampling in their plugins.
Does Oversampling Even Matter?
Admittedly, oversampling seems like a pretty insignificant function - it doesn’t do something
super noticeable, especially when observed on one plugin; despite this, it definitely
plays a big part in creating clean mixes and masters. Although you may not notice it at
first, oversampling remedies distortion in a big way.
If you value reducing clipping distortion, aliasing distortion, and to a lesser extent,
lowering quantization distortion, you should definitely use oversampling.
Additionally, if you want to have accurate analog emulation without the negative impact
of digital sounding aliasing distortion, use oversampling.
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