TSAR-1 Predelay and Diffusion
Eddie Bazil, December 2012

One of Softube's most popular plug-ins is the TSAR-1 Reverb. It was designed for fantastic sound and ease of use, but some of the concepts in the settings not familiar to all users. In this article, we'll take a closer look at the Predelay and Diffusion settings.

We have been listening to music acoustically for thousands of years. The acoustic space in which the instruments are sounding plays a huge role in the overall tone and feel of the perceived sound. This is why it is so crucial to have access to some great reverb effects in mixing. Check out the Creating a Sense of Distance article for some basic reading on the different components of a reverb (and in particular the early reflections). A brief summary can also be found to the right.

Brief summary of the components of a reverb

Direct sound - the sound from the sound source itself.
Early reflections - the first sound reflections that bounces off the surfaces of the acoustic environment and reach the listener.
Reverb tail - the sound of reflections bouncing back and forth in the acoustic space.

See the Creating a Sense of Distance article for more detail and the graphical representation below.

Of course, all the parameters governing reverb are important but the two specific functions that often seem to be overlooked are predelay and diffusion. When the sound is triggered, a certain time passes after the listener hears the direct sound and early reflections - and before the reverb tail begins. In TSAR-1, this time is what is known as the predelay. For some other reverbs, predelay denotes the time between the direct sound and the early reflections. But again, in TSAR-1, the predelay controls the amount of time taken before the reverberated sound begins. By adjusting this parameter you can impress a change in the perceived size of the room. The longer it takes for the reverberation to build up, the larger the room will seem.

Although this is the first and foremost port of call when dealing with reverbs, the accepted thinking is that it only affects the distance and therefore reflective qualities of an environment. But I have found that predelay is my best friend when it comes to separating the dry signal from the wet signal. I have now moved away from thinking in terms of distance and reflective properties and entered the land of separation. If you ever encounter a situation whereby you have sculpted a wonderful spatial reverb and your sounds sit beautifully in their respective spaces but for some obscure reason the attack transients of the sounds seem to have been cloaked in reverb then that is the best time to use predelay to separate the reverb from the dry sound.

Diffusion parameters control the spacing in between the early reflections. The tighter these reflections are packed, the thicker the sound, and vice versa. So the more diffusion you apply the thicker the reverb will sound. This can give a "dark" or "confined" impression of the room sound. If you apply less diffusion, the opposite happens; you space out the reflections further apart and make for a more sparse and "echo-y" reverb sound that takes up less room in the mix.

For some reason many people seem to head straight for the HF damping or some form of post reverb EQ whilst ignoring the power of diffusion to control the thickness and how much real estate of your mix the reverb takes up. I find that diffusion helps to really tighten and thicken the reflections and this can be so helpful when deciding on the type of energy emitted within an environment. I tend to couple predelay with hefty amounts of diffusion if I am hankering after the dark and snappy snare effects that sit nicely in heavy dance music. Whereas EQ and HF damping can help shape the tonal quality of the reverb, diffusion sculpts the reflective qualities of an environment and that can work more naturally in your favor. Diffusion is also a great function to head for when working is sound design and specifically sound effects as the sheer energy and thickness can help in shaping dense sonic structures and fooling the listener into thinking that a specific environment exists whereas it doesn't.

Predelay and diffusion play an important part in structuring and shaping the environment's qualities but can also go further in shaping reverb both creatively and in extreme measures.

© 2012 Eddie Bazil
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