Although dithering is an important step of the mastering process, knowing how to use it, when to use it, and why you should use it will improve your recordings and final mastered audio files.
What Is Dither?
Dither is low volume noise, introduced into digital audio when converting from a higher bit-resolution to a lower bit-resolution.
The process of reducing bit-resolution causes quantization errors, also known as truncation distortion, which if not prevented, can sound very unpleasant.
To understand this better, we must understand bit-depth.
What Is Bit-Depth?
In the digital audio domain, bit-depth is what defines the number of measurement values to describe the amplitude of a single audio sample. Each bit effectively represents 6db of dynamic range.
For example, a recording made at 24bit-resolution would have a potential range of 144db. (See figures 1-2 below).
As one reduces the bit-depth, such as from a 24bit-resolution sample to a 16bit-resolution sample, you are reducing the number of values available to measure the amplitude of any given sample.
In other words you now have less values available to describe the dynamic range of your audio. (see figures 3-4 below).
As a result, certain values that are no longer there will be forcibly rounded off to the next closest value.
This truncation results in the loss of very low signal levels, and the creation of audible distortion where the values have been rounded, squaring off the waveform. (see figures 5-6 below).
How Does Dither Prevent This?
If you apply dither to a silent audio file, and turn the volume way up, you can hear the sound of dither alone.
You might even see this visually if you add an EQ to the end of your production chain and see the noise moving around even though there is no audio coming from the speakers.
Introducing this subtle noise to an audio file prior to reducing the bit-depth eliminates the truncation distortion. You are in effect trading the distortion for noise.
Given this information, one could determine that the use of dithering on a 24bit sample, and exporting in 24bit or higher resolution bit-depth would be ineffective, as there is nothing being replaced with noise, and is only necessary when down-converting to a lower bit-depth.
The Computer Screen Analogy
To help better understand dithering, I like to use the hand over your computer monitor analogy. How it works is you start by holding your hand over your computer monitor.
Notice that you can see your computer monitor perfectly with the exception of the block where your hand is.
Now, if you wave your hand rapidly back and forth from left to right across the screen (applying dither), it allows you to see the entire screen as apposed to blocks of the screen.
Now that you have a better understanding of what dithering is, you might be asking yourself, “why dither?” Especially if you can just keep your 24bit-resolution file and avoid dithering altogether.
The answer is simple; all finished, mastered audio files are 16bit. Although 24bit is a higher quality sound with more audio detail, and eliminates truncation distortion altogether, the reality is that 90% of all playback devices are 44100/16bit.
Which means if you try and play a 24bit audio file through one of these 16bit playback devices, it will sound like shit.
In this regard, you should keep the consistency of bit-depth throughout your production process from beginning to end. If you are producing in 24bit and your playback is set to 16bit, then you should be using a dithering tool in your production chain.
If you are recording and producing in 16bit, and your playback is in 16bit, then there is no need to dither. If you are producing in 16bit, and your playback settings are 24bit, there is no need for dithering.
What are the current settings of your project? What are the current bit-depth of your samples? What is your playback bit-depth settings set at? These are all things you should know when producing your track.
Note: If you intend to have your song mastered, it is best to export at the same bit-depth or higher as your project settings are set to. For example, if you are producing in 16bit, be sure to export in 16bit or higher.
If your project settings are in 24bit, and you export in 16bit without dithering, your audio file is damaged before it even goes to the mastering engineer.
Types of Dither Algorithms and Shaping Options
Many dithering options offer noise shaping. Noise shaping allows you to add an eq curve to the dither noise, helping move the energy of the noise to less audible regions within the frequency spectrum for an even better result.
Here are a few popular types. (I will be using Ableton’s dithering options, though is very similar options in all programs)
- Triangular – By default, Triangular is selected, which is the safest mode to use if there is any possibility of doing additional processing on your file.
- Rectangular – Rectangular mode introduces an even smaller amount of dither noise, but at the expense of additional quantization error.
- The Three Pow-r Modes – The three Pow-r modes offer successively higher amounts of dithering, but with the noise pushed above the audible range.
The Images Analogy
Image dithering works the exact same way and is no different than audio dithering. Below are four images.
From left to right, the first image is an 8 bit image at full resolution, next is the same image reduced to 1 bit with no dithering, 3rd is the same greatly reduced image with dithering added, and lastly in image 4 is the reduced bit image with added dithering, plus noise shaping option added. (see figure 8 below).
Last Notes and Conclusion
Note that dithering is a procedure that should only be applied once to any given audio sample. If you plan to do further processing on your rendered audio sample, it’s best to render to 32-bit to avoid the need for dithering at this stage.
Lastly, you only want to dither your rendered audio if it’s final. If you’re sending it to someone else for mastering, or it’s just not yet the master, then don’t dither.
Regarding which mode is best, it’s really best to use your ears and spend some time with the results.
Images provided by izotopeinc – http://www.youtube.com/user/izotopeinc?feature=watch
*Helpful Video Demonstrations: