Can You Hear the Effects of Dithering?

Date:2020/2/22 17:22:50 Hits:

Certain topics are pretty much guaranteed to light up internet forums, like Mac vs. PC, Les Paul vs. Strat, and dither vs. well, different kinds of dither, and whether dither is even necessary — or some scam perpetrated on us by audio PhDs who don’t live in the real world. And like so many esoteric audio concepts, the answer is: it depends.

You can go deep down into technical rabbit holes with dither, so we’ll do more of an overview. Most importantly, we’ll describe how to evaluate dither objectively and decide what sounds best with your music.

What Is Dither, Anyway?
Today’s hard disk recorders most likely have an audio engine with at least 32-bit, floating-point resolution. But currently, although there are some high-resolution audio formats intended for consumers, your mix usually ends up streaming online in MP3 or AAC format, or in what’s still the most common physical delivery medium — a 16-bit/44.1kHz CD.

Dither — the noise added to an audio signal prior to quantization or word-length reduction to minimize the resulting distortion and noise

Before dithering, an audio file’s “extra” bits (for CDs it was anything beyond 16-bits) were simply truncated (discarded) when creating the CD master. This meant that, for example, decay tails below the 16-bit resolution limit just stopped abruptly. Maybe you’ve heard a buzzing sound at the very end of a fade-out or reverb tail; that’s the sound of quantization noise, which occurs because the least significant bits can’t reproduce smooth audio variations. Dithering is a process that adds a controlled type of noise to the audio signal, which can reduce (or even eliminate) quantization noise at the lowest levels.

It may seem odd that adding noise can improve the sound, but psycho-acoustics is on our side. Any noise added by the dithering process has a constant level and frequency content, so our ears have an easy time picking out the content (signal) from the noise.

This article’s focus is on understanding how dither affects your audio. Note that we’ll reference audio examples when appropriate, but individual files are included for loading into your DAW to make for easy comparisons.

Experiment #1: Can You Really Hear Low-level Audio?
This is an experiment to do in your DAW, so download the audio WAV files by clicking here.

Load the stereo 24/44.1 Reference File.wav into your DAW, and set the volume for a comfortable listening level.
Normalize the file to -60dB without changing the listening level.
Unless your idea of a comfortable listening level is to blow your ears off, playing the reference file back at -60dB will be inaudible or at least very faint. Bear in mind that this is the kind of level (and lower) where dithering does its thing.

As a result, dithering has the most impact with music that has wide dynamics, doesn’t necessarily hit 0 very often (if at all), and is at a fairly loud playback level. For example, you won’t hear the impact of dithering on pop music that’s always kissing 0dB, but you may hear it on the reverb tails of acoustic symphonic recordings playing back from 16-bit CDs.

Experiment #2: Quantization Noise with 16-bit Audio
Let’s hear what quantization noise sounds like.

Load the file -80 no dither 16-bit normalized.wav. This file is the result of normalizing the 24-bit reference file down to -80dB, exporting it as a 16-bit file with no dithering, and then normalizing it to full volume to hear the actual quantization noise.
Play back the file. It should sound like your worst audio nightmare — that’s the quantization noise.
-80 no dither 16-bit normalized.wav

Load the file -80 no dither 24-bit normalized.wav.This file was also normalized to -80dB, exported with no dithering, and normalized to full volume.
Play back the file. It should sound very much like the reference file, because its lower 8 bits weren’t truncated, so there’s no audible quantization noise.
-80 no dither 24-bit normalized.wav

This experiment also brings up an interesting side note about 24-bit/96kHz “high-resolution” recordings: Maybe it’s not the high sample rate that causes people to think this format sounds better, but the 24-bit resolution.

Experiment #3: What Dithering Sounds Like

Although we’ll be applying dithering to extremely low-level signals, we’ll normalize them to 0dB in order to hear the dithering in a really obvious way. (But remember how in Experiment #1, -60dB is a really low level, and these examples use audio that’s even 20dB quieter — so, of course, the noise will be prominent.) The following files are all 16-bit.

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