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Audio Dithering: Why It's More Than Just Adding Noise

April 2, 2023 
Last Updated on May 6, 2023

In the world of digital audio processing, audio dithering is a term that's frequently thrown around but not always fully understood. At its simplest definition, audio dithering refers to the addition of noise to an audio signal. This noise is added to reduce the distortion and artifacts that can occur when converting an audio signal to a lower bit depth.

But, audio dithering is more than just adding noise; it's a crucial step in digital signal processing that can have a significant impact on the overall audio quality of a master.

In this article, we'll explore the ins and outs of audio dithering including why it's important and when to use it. Let's dig in!

What Is Audio Dithering?

Example graph of audio dithering.
Credit: Wikimedia Commons

Audio dithering is a process that involves adding low-level noise to a digital audio signal before reducing its bit depth. The noise is typically white noise which has a flat frequency response. This is done to reduce the quantization distortion that can occur during the conversion.

When an audio signal is digitized, it is represented by a series of binary values that correspond to the amplitude of the signal at each sample point. The number of bits used to represent the signal determines the resolution of the digital representation of the analog signal. For example, a 16-bit signal has a resolution of 65,536 possible values, while a 24-bit signal has a resolution of over 16 million possible values.

When reducing the bit depth of a digital signal, the quantization error can cause distortion, particularly in low-level signals. Dithering adds a small amount of noise to the signal before reducing its bit depth, which helps to randomize the quantization error and reduce distortion.

The Different Types Of Audio Dither

Audio dither comes in several different flavors, but these 3 are the most common. Each of these types have distinct characteristics that may be beneficial in different situations. Let's first discuss triangular dither.

Triangular Dither

Triangular dithering, also known as TPDF (triangular probability density function) dithering, is a type of dithering that uses a triangular probability density function to add random noise to the digital signal. The noise is added in such a way that it is equally distributed across the frequency spectrum, which helps to reduce quantization distortion. Triangular dithering is often used in audio mastering and is particularly effective for reducing harmonic distortion in low-frequency signals.

Rectangular Dither

Rectangular dithering, also known as noise shaping dithering, is a type of dithering that uses a rectangular waveform to add random noise to the digital signal. The noise is shaped to reduce quantization distortion by shifting the noise energy away from the most sensitive frequency ranges. This type of dithering is particularly effective for reducing distortion in mid-to-high frequency signals.

POW-R Dither

POW-R dither is a specific type of dithering algorithm that was developed by the mastering engineer and audio processing expert, George Massenburg. The name "POW-R" stands for "Psychoacoustically Optimized Wordlength Reduction". The goal of POW-R dither is to reduce the quantization distortion while also minimizing the perceived increase in noise that can occur with dithering.

POW-R dither uses a combination of noise shaping and noise modulation techniques to minimize the amount of noise introduced during dithering. It employs a complex set of algorithms to shape the dither noise in such a way that it is more effectively masked by the audio signal, resulting in a perceived reduction in noise.

POW-R dither also takes into account the specific characteristics of the human auditory system to ensure that the dithered audio signal is as transparent and natural-sounding as possible. This is accomplished through careful attention to the spectral characteristics of the dither noise, as well as the timing and amplitude of the noise modulation.

POW-R dither has become the most popular dithering algorithm in the professional audio mastering community, and is widely used in many high-end digital audio software and mastering tools. It is known for its ability to produce natural-sounding audio with minimal noise, making it a valuable tool for preserving the quality of digital audio signals when converting between different bit depths.

When To Use Audio Dither

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The dithering function should be used anytime you want to reduce the bit depth of an audio signal. This is typically at the end of the mastering process.

Many songs are recorded and mixed in either 24 bit or 32 bit float depths. If we want to get the song ready for a redbook audio (CD) release, we need to convert the bit depth down to 16 bit.

If you are strictly doing a digital release and the audio is at 32 bit float, then my recommendation is to convert it down to 24 bit. It is always best to check with your digital music distributor on what formats they allow.

Related Article: What Is Audio Mastering And How Can Your Music Benefit From It?

Best Practices For Audio Dithering

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Now that we understand the importance of audio dithering and when to use it, let's explore some best practices for using dithering in digital audio production.

First and foremost, it's important to select the correct algorithm when applying dither. As mentioned earlier, there are several different types of dithering algorithms, each with its own characteristics and strengths. Understanding the differences between these algorithms and using the right one for the situation can make a significant difference in the quality of the final recording.

When adding dither it's also important to use the correct amount of noise. Adding too much noise can result in a loss of dynamic range and signal-to-noise ratio, while adding too little noise may not provide enough smoothing of the quantization errors. Most digital audio workstations and plugins provide settings for adjusting the amount of dithering noise added, allowing users to fine-tune the dithering process for optimal results.

Finally, it's important to use dithering throughout the entire digital audio processing chain. This means using dithering when adding non-matching bit depth samples, when processing audio effects, and when rendering the final mixdown. By using dithering consistently throughout the entire process, the benefits of dithering can be maximized, resulting in a cleaner, more natural sound.

Common Misconceptions About Audio Dithering

Despite its importance in digital audio production, there are several common misconceptions about audio dithering that are worth addressing.

One of the most common misconceptions is that dithering is only necessary when converting 24-bit audio to 16-bit audio. While it's true that dithering is often used when downsampling from 24-bit to 16-bit audio, it's also important to use dithering when recording and processing audio at higher bit depths.

Another misconception is that dithering always results in a loss of signal-to-noise ratio. While it's true that adding noise to a signal will increase the overall noise floor, the amount of noise added in the dithering process is typically very small and is barely audible. In fact, in most cases, the benefits of dithering far outweigh the slight increase in noise.

Finally, some people believe that dithering can be used to "fix" poor quality recordings. While dithering can help to minimize the effects of quantization errors, it can't fix poor quality recordings that are the result of other issues, such as poor microphone placement or low-quality equipment.

Final Thoughts

In conclusion, audio dithering is a crucial process in the digital audio production workflow, particularly in mastering. It involves adding low-level noise to an audio signal before reducing its bit depth, which helps to prevent distortion and artifacts caused by quantization errors. By distributing the error evenly across the frequency spectrum, dithering can improve the sound quality of a digital audio file and maintain the fidelity of the original recording.

With the ever-increasing demand for high-quality digital audio, understanding the role of dithering in the production process is essential for achieving professional-level results. By using dithering appropriately, audio professionals can ensure that their digital audio files are of the highest possible quality, with minimum distortion and artifacts.

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