Algorithmic and Convolution Reverb

I’m Will Servant and I’m an old fart who started playing music back when drums were animal skins stretched over hollowed out logs, struck by wooly mammoth bones. I am enjoying this course immensely and have learned a great deal so far. As I do not currently have a DAW to use I am presenting today’s lesson by way of text. I hope you are able to follow the lesson and comprehend it easily. If you cannot, please let me know how I can do a better job. Thanks for your help.

When it comes to reverb let me begin by saying we should all be thankful for the digital reverb plugin. Analog methods of adding reverb could be cumbersome and parameters such as delay time and pre delay could not be easily controlled.

There are two basic types of reverb plugins that give the producer the tools to create a reverberation effect that accurately represents a real space. They both use math to create reverb effects, but do so in a different manner. In describing these two types of reverb I’d like to go into a bit more depth than did the video lectures. I hope you can bear with me.

Algorithmic reverb uses mathematical formulas to apply different parameters of reverb to the signal. An algorithmic reverb allows the producer a lot of flexibility. They can manually control the functions that make up reverb, to create a highly customized reverb environment. A convolution reverb uses math formulas to analyze the impulse responses of recordings of real physical spaces, then applies the total reverberation effect of any given space to the track.

One analogy used to describe the difference between the two types of reverb plugins is that algorithmic reverb is similar to a synthesizer. It uses math to control each component separately combining them to create the reverb effect. Convolution reverb is like a sampler. It uses recordings of real spaces to create separate, complete reverb environments.

An analogy I like to use is that of making soup. The algorithmic way of making soup uses the various separate ingredients, i.e. a homemade soup. Using this method you are in control of the parameters, the ingredients, their relative amounts, the temperature and timing of the cooking. You come up with a meal that is uniquely yours. However, you need to have knowledge of how the soup is supposed to taste to avoid serving one up that nobody likes. You can also create and use recipes, which are like algorithmic reverb presets, where all the parameter settings are in memory for you to easily apply. The downside here is that these presets/recipes are only approximations of the type of soup you want. To really be creative you must have knowledge of how to cook, in order to get the meal you want.

A convolution soup is when you go to the store and buy readymade soup. There are a wide variety of soups you can buy. They are all different and the ingredients have been put together already, from a standard recipe that somebody else created. You choose the one you want to eat. Any one type of any brand of soup will be universally the same in flavor, texture and consistency. In this circumstance you need to know what kind and/or brand of soup you or your guests might like. They may like a school gym instead of a concert hall or night club, as it were. You may also want to know which soup goes best with the beverage you are serving, i.e. which reverb sounds best on which track. The downside here is that you don’t have a lot of control over what comes out of the can. To use a tired and overused bromide, it is what it is.

To use an algorithmic reverb you need to know a little about controlling the functions that comprise reverb. Most algorithmic reverb plugins have two distinct control sections, early reflections and diffuse reverb. These model how reverberation works in real spaces. Early reflections are the numerous delays caused by the sound reflecting off close surfaces. Diffuse reverb is those delays diffused, or carried out farther into the space. Elements of early reflection are pre delay, which is the length of time between the original sound and the beginning of the reverb effect, room shape and/or size, and use of the stereo soundscape. Elements of diffuse reverb are delay time, high frequency EQ, density of the reverb effect, and once again, when the effect starts, and how it is spread in the stereo width.

Using convolution reverb is essentially a function of listening to the reverb from any number of spaces, as they are applied to the track, and then choosing the one you feel works best for your purposes. It’s obviously a little simpler to use than algorithmic reverb but has fewer permutations and is therefore less flexible. It can also be overwhelming trying to listen to the sound of many different spaces, especially when the reverb from a particular space can sound different in the full mix than when heard on a soloed track.

In summary, both types of digital reverb processors have advantages and limitations, and both are equally as valuable to the producer in creating the atmosphere and sound environment they want the listener to experience. Both are very useful tools in finalizing a mix. But, as in most aspects of producing, our greatest tool is our ears, and listening is the best way to find which kind of reverb is best for your project. Through trial and error you can find that “just right” balance between the chicken and the vegetables, but remember to use your spices sparingly, so that your guests barely know the reverb is there.