This article is the first in three carrying on the current theme of adding stereo width to a mono source, but, as reverb is a broad topic i have divided it into a series of 3 articles. If you haven’t already done so, don’t forget to take a look at both parts 1 & 2 of ‘Adding Stereo Width To A Mono Source’ for some background.
This series will investigate what reverb can tell us about our environment, how we can recycle old songs to create our own reverbs effects using convolution reverb; and look at creating ways of implementing reverb in Logic.
Hearing the walls
When someone speaks to you, it is likely that some of the sound waves travelled directly towards you. But imagine your were positioned somewhere else in the room… would you have still heard the speaker? The chances are that you will have given it was a small enough room because sound travels in many directions at once. When we hear someone speaking to us we don’t just hear the direct sound but also some of these indirect sounds after they have reflected off the surfaces around us.
Sound waves travel in a straight line, and at room temperature this happens at roughly 340 meters per second. As a result sound that has traveled directly to our ears arrives before any that took a more indirect route. And because we have two ears it is more than likely that some of these sounds arrived at slightly different times and slightly different intensities. These differences in time of arrival and intensity can help us locate direct sounds, as well as subtle changes in frequencies, but in reverberated sound they also provide incredible amounts of information about our surroundings.
Lucas was born blind but uses clicks he produces with his mouth to ‘see’ his surroundings: https://www.youtube.com/watch?v=LqjyUHpg2lY
So reverb is a large collection of echoes that hang around (or persist). These can come from any given number of directions depending on what surfaces they bounce off. Some surfaces are naturally more reflective than others, and some reflect some frequencies better than others. The frequencies reverberated back to the listener, the time between these reflections, and the time it takes for reflections to fade out completely interpreted by our brains and provide us with clues as to the characteristics of the space that produced them.
For example, the reverb phenomenon ‘flutter echo’ is caused by two parallel surfaces reflecting sound back and forth between two hard surfaces. This causes the sound to appear ring as the reverberations quickly alternate direction. The closer the surfaces causing the effect the higher the pitch of the ringing sound created. Therefore if we encountered two spaces with flutter echo at different perceived pitches you could assume that the higher pitched ringing sound was caused by a smaller space. Also, flutter echo is characteristically less likely in larger spaces because the further a sound travels the more energy it looses.
By using a reverb plugin to a source you can artificially create space for a pre-recorded sound. Some plugins such as Logic SilverVerb or PlatinumVerb use algorithms to create artificial spaces which allow you to manipulate different parameters such as room size or shape which in-turn colour the sound they create. Or my favourite in Logic, Space Designer, can also use an Impulse Response (IR) sample to recreate the reverb of a real space. So with the appropriate recording you could reproduce the reverb of a given point place in St Paul’s Cathedral, Abbey Road Studios or the crypt at Canterbury Cathedral.
An impulse response is an audio file that documents the reverb in any given space usually by making a short noise such as a ballon pop or a starter pistol. This method of creating reverb does have it’s flaws though, as it is a static recording and never changes, but it is perhaps the most realistic artificial reverb to date.
We can use the properties of reverb to our advantage when mixing sound. Sometimes reverb can help gel different sounds together by locating them in the same space, and conversely you may wish different sounds to occupy different spaces in order to direct the listeners attention – it’s all about context! Stereo information can also be added to a mono signal by applying reverb, but, even mono reverb will add a sense of space because our brains are accustomed to associating reverberations with the spaces that create them. You may wish to limit the amount of stere information in a track for various reasons and mono reverb can be a great way of creating a sense of space without using using using the stereo field.
For further reading on reverb check out these pages: