When you first get into audio production, you’ll encounter several foreign words and phrases that will either fly past your radar or leave you puzzled; bit depth, attenuation, sidechaining, etc. (the lexicon is seemingly endless). Perhaps one of the most common examples of this is the term “dithering.” Whether or not you’ve seen this word before, its meaning isn’t abundantly clear. And yet, dithering is one of the most essential and useful tools in the mixing and mastering arsenal, so it’s a good idea to get acquainted with it. So, what is dithering, exactly? When and why is dithering used? And what are the different types of dithering for audio?
We'll answer all these questions and more in this article, and try to make the concept of dithering as digestible as possible.
What is Dithering?
There’s a lot of depth to dithering, so we’ll begin with a simple definition. Dither is noise . To go a bit further, dithering is a particular form of distortion.
More specifically, dithering is a process wherein a small quantity of noise (i.e., white noise) is combined with an existing audio (or image/video) signal to help maintain its overall quality when lowering its resolution.
Watch this video by Rowntree Audio below for a quick and easy dither demonstration:
[VIDEO EMBED] https://www.youtube.com/watch?v=cLnuoQ6pIKk
At first glance, this might seem unnecessary and even counterintuitive. After all, if your goal is to put the highest-quality music out there, why would you want to add noise or downsample it in the first place? And how does adding noise to a signal help it sound better or more dynamic?
To understand the answers to these questions, you must first get a grip on how digital audio works.
What Dithering Has to do with Digital Audio
Audio can be broken up into two basic categories: analog and digital. Whereas analog audio is a continuous stream of sound waves, digital audio is a blocky, number-based representation of the “real deal.” So, whenever you record something into your digital audio workstation (DAW) , the software “samples” the inputted audio and creates a digital copy via analog-to-digital (ADC) conversion.
As long as you’re recording with modern digital tools at the proper “sample rate” (usually 44.1 kHz) and “bit depth” (usually 24-bit or 32-bit float), this digital version should sound virtually identical to the analog input. The sample rate is a measurement of how many samples per second are extracted from the analog signal to create the digital version, and bit depth refers to digital audio resolution, i.e., the amount of information packed into each sample.
Cutting Signals Down to Size
Now, if we all had unlimited processing power at our disposal, we could theoretically record, export, and listen to a digital audio file at infinitely high resolutions. Of course, this isn’t the case. We must instead make some concessions to get a recording from point A to point B. It’s a matter of what’s manageable – while you’ll be recording at a 24-bit or 32-bit depth (or higher) in most DAWs, most audio playback devices and formats only perform at a 16-bit resolution (Spotify and Apple Music, for instance, stream 16-bit audio at a sample rate of 44.1 kHz).
If you want your music to be as accessible as possible, you must reduce your high-quality recordings to fit these various formats. Thus you must downsample your audio files (i.e., drop it to a lower bit depth) upon exporting them. At the same time, you don’t want to eliminate your audio’s nuances and dynamics during bit depth reduction.
This is where the power of dither comes into play.
Dithering: Clarifying a Distorted Concept
Without applying dither, what would happen when converting digital audio from a higher resolution to a lower one? As you might imagine, those blocky numbers (the ones that represent the incoming signal) we mentioned earlier would become crunched and even blockier, turning what used to resemble a somewhat continuous wave into something more like a staircase. This process is called truncation and results in what's known as quantization error, quantization distortion, or quantization noise.
If you’re familiar with waveforms and how different configurations sound based on appearance, you know that this step-like form sounds distorted. More specifically, downsampled audio that isn’t dithered yields harmonics that are correlated to the original audio signal and cut through the human ear quite loudly (harmonic distortion).
The last thing you want is for unintentional, noisy distortion to run throughout your pristine audio, of course. When you add low-level dither noise to the audio prior to the quantization process, this harmonic distortion is essentially scrambled and loses its presence significantly.
Ultimately, dithering allows your mix to maintain its dynamic range and original overall sound when getting docked to a lower resolution.
Dithering Relies on Random Variation
If the concept of dithering still isn’t crystal clear, remember that it’s all about randomization. The noise that dithering adds to your audio is random and uncorrelated (think “hissing” sound given off by white noise). As a result, those loud correlated distortions that occur when reducing the bit depth of your audio aren't allowed to poke through.
This concept of adding random noise to something occurs during image processing, too. Imagine looking at a crisp image on an HD TV. Then, imagine viewing the same image on an older TV with a much lower resolution. Plenty of data would be lost in this process, creating a pixelated picture rife with color banding (which occurs when color information isn't accurately represented).
This transfer from high definition to low definition could be smoothed out via dithering. Instead of directly cramming the image into a smaller space, the image’s information is first scrambled, reducing the amount of color depth. In the end, the downsampled image retains its relative shape, color, and structure.
The picture below will give you a better understanding of how dithering works on images.
On the left, you'll see the original image with all its smooth curves and gradients. The middle image shows what happens when the source is truncated into a smaller resolution without adding dither -- you can see significant pixelization and color banding. Finally, the righthand image represents the image at the same resolution as the middle version but with noise added prior to downsampling. While still presented at a lower resolution, this final image better represents its original source in terms of both shape and color.
When to Use Dithering
So, when should you add dither to audio? As a basic rule, dithering should always occur whenever you downsample audio (often in the mastering or exporting stage). Put another way, use dithering whenever quantization distortion shows up in your audio (which it will when changing bit depth from higher to lower).
As a general rule, exporting and mastering audio almost always calls for dithering , whether your DAW does it for you automatically or you handle it manually. In most cases, mastering involves squashing a 32-bit float or 24-bit audio file into a depth of 16-bits, so adding dither is called for here.
Dithering should almost always be performed during bouncing or exporting, or otherwise used as the final effect in a signal's chain (some limiters feature a dithering function of their own).
When Not to Use Dithering
Just because dithering is standard practice in digital audio production doesn't mean it's always necessary, however. If you're preparing a track for mastering via a mastering engineer or eMastered, for instance, you should avoid dithering your audio, as this will be handled for you (as mentioned above, dither is commonly used during the mastering process).
You also might not need to dither if you’re exporting audio at a high resolution (i.e., 32-bit). And hold off on dithering when convertng audio to formats such as AAC or .mp3 , as these processes will compress the sound on their own.
You can sometimes get away with dithering even when it's not called for. In some cases, the noise added won't be audible enough to change much of anything in your audio. At worst, however, your track can end up with a noticeable hiss that no one wants to hear. To be safe, then, follow the rule mentioned above: only use dithering to conceal quantization distortion (i.e., when exporting audio from a higher bit-depth to a lower one).
Different Types of Dithering
As if the concept of dithering alone wasn't difficult enough to grasp, there are multiple kinds of dither at your disposal. For better or worse, there are no major differences between these dither types -- none that are noticeable to the average ear, anyway. Still, each type of dithering adds a different kind of low-level noise to the audio depending on its current dynamic range. Some types of dither even feature noise shaping, wherein specific frequencies are attenuated or boosted on an equalization (EQ) curve.
Different DAWs and plugins offer different dither variations. In Logic Pro X, for instance, you can employ three main dither types upon bouncing: POW-r #1, POW-r #2, and POW-r #3. The correct dithering setting for your purposes will mostly depend on the dynamic range of your audio.
POW-r #1 Dithering
This first category of dither offered by Logic Pro doesn't offer noise shaping and is best used on mixes with low dynamic ranges.
POW-r #2 Dithering
Primarily used for speech (i.e. podcast or radio broadcasts), POW-r #2 dithering (noise shaping) reduces noise in the 2kHz frequency range and boosts it around 14kHz and beyond, all while concealing quantization distortion. This gentle equalization works well for clarifying many vocal types.
POW-r #3 Dithering
As for Logic Pro's third dithering option, POW-r #3 dithering (noise shaping) works best for highly dynamic mixes, such as acoustic, orchestral, or big band music. The noise modulation/equalization deployed by this type of dithering goes beyond that of POW-r #2, which makes sense for more dynamic recordings.
Other Types of Dithering
When exploring other DAWs and limiter/noise shaping plugins, you might come across terms like "none," "moderate," and"ultra." These words refer to the amount of dither applied to a given signal. Generally speaking, the noise shaping offered by different types of dither clamp down on the signal's lower frequency content (2kHz area) and amplifies its higher frequencies.
Should I use dither?
If you're downsampling your audio from a higher bit depth to a lower one (i.e., 32-bit fixed point to 24- or 16-bit), you should employ dither.
When should you dither audio?
Always use dither when exporting, bouncing, or mastering your audio. Put another way, use dither when lowering the bit depth of your track.
Should I use dithering when mastering?
Yes. In fact, the mastering process is often the best juncture to use dithering, as it will conceal any unwanted quantization distortion before lowering the audio's bit depth. This way, your track will be ready for playback on a variety of platforms and devices.
Can you hear dither?
A: If you dither your audio properly, you won't hear the low level noise at all, especially in context. Of course, it's possible to hear dither if you were to apply it to a silent audio files and boost the volume significantly. Dither will sound like some variation of white noise (a soft, consistent, hiss).
Can you hear a difference between 16-bit audio and 24-bit audio?
A: Unless you have a well-trained ear or are listening to a highly dynamic piece of music on high-quality speakers, you won't likely notice any difference between 24-bit and 16-bit audio.
Which noise is useful for dithering?
White, brown, and pink noise can all be useful for dithering. These are all variations of that "hissing" sound you might recognize from tuning a radio. White noise is spread out across the frequency spectrum, brown noise is on the lower end, and pink noise falls somewhere in between.
Is blue noise dither preferable?
Blue noise dithering is beneficial for maintaining an image's fidelity when lowering its resolution at significantly low sample rates. Proceedings of the IEEE has a comprehensive study on this phenomenon here .
Does dithering make a difference?
Yes, especially if your song features a high dynamic range. Dithering your audio properly when reducing its bit depth will reduce quantization distortion while maintaining or enhancing its dynamics.
Should I dither for Soundcloud?
Because Soundcloud plays tracks at 16-bits (and 48 kHz), it's usually wise to dither your track before uploading it there. Note that Soundcloud optimizes all audio for streaming and also offers an algorithmic mastering tool to users. You can read more about Soundcloud's upload recommendations here .
The Bottom Line on Dithering
Dithering is one of those concepts/tools that sounds more complicated than it really is. Ultimately, dither is some type of low-level noise you can add to your audio to reduce quantization distortion when lowering its bit depth. Before submitting your track to eMastered for mastering, we suggest you export your audio at the highest possible format both in terms of bit depth and sample rate (i.e., 32-bit, 48 kHz). From there, we will apply dithering to your audio as necessary.