When designing audio we are often thinking of time across a large variety of units: samples, milliseconds, frames, minutes, hours and more. This article is inspired by a conversation I had with Andy Farnell about a year ago at a pub in Edinburgh, right before a sound design symposium, where we discussed about time and the role it plays when it comes to designing audio.
Like most other audio designers out there, I started twiddling the knobs and sliders well before I had an understanding of the underlying DSP. It was eye-opening experience to realise that almost every single DSP effect is related to time. So let’s start looking at a few common DSP tools used in everyday sound design and analyse how time and the precedence effect plays a role, starting from hundreds of milliseconds all the way down to a single sample.
The precedence effect is a psychoacoustic effect that sheds light on how we localise and perceive sounds. It has helped us understand how binaural audio works, how we localise sounds in space and also understand reverberation and early reflections. From Wikipedia:
The precedence effect or law of the first wavefront is a binaural psychoacoustic effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single fused auditory image; its spatial location is dominated by the location of the first-arriving sound (the first wave front). The lagging sound also affects the perceived location. However, its effect is suppressed by the first-arriving sound.
You might be familiar with this effect if you’ve done any sort of music production or mixing. Quite often a sound is hard panned to one of the two stereo speakers and a delayed copy (10-30ms) of the sound is hard panned to the other speaker. Our ears and brain don’t perceive two distinct sounds, but rather an ambient/wide-stereo sound. It is a cool technique for creating a pseudo-stereo effect from a mono audio source.
The first 30 seconds in the video below shows an example of the precedence effect in action. The delayed signal smears the original signal with phasing artefacts after which it seems to split from the original signal and become a distinct sound of its own.
Echos And Reverb
Echos are distinct delays. Reverberation is made up of early reflections which are delayed sounds that arrive first at the listener (right after the direct sound) followed by a tail that consists of many such delays diffused into a dense cluster. Artificial reverbs are quite often approximated using networks of delays that feedback into each other (convolution reverbs behave a differently).Read More