Reverb 101: Size

One of the most commonly found parameters in digital reverbs is Size. This parameter is sometimes a percentage, but in other cases it is given in meters or cubic meters. But what does Size mean in a digital reverb?

How does Size work?

In most digital reverbs, Size is used as a scalar for some/all of the delay lengths that make up the digital reverb network. A smaller Size value will reduce the length of the delays in the reverb algorithm, while larger Size values increase the length of the delays.

What are the sonic effects of the Size setting?

When the Size parameter is increased in a digital reverb, you will often hear the following effects:

  • A slower attack to the reverb. The diffusion and early reflection networks in a reverb are often tied to Size. If they are, increasing the Size will cause the diffusion to build up more slowly, and increase the spacing between the delays in the early reflections. This causes the reverb to fade in more slowly, and helps to separate the reverb from the source material.
  • Less metallic decays. Larger Size settings will increase the length of the delays in the reverb tail, which increases the resonance (eigenmode) density. A higher resonance density is what you find in larger rooms and halls.
  • More discrete echoes in the initial part of the decay. This can sound grainy when processing sources with strong transients, such as percussion or vocal sibilants.
  • If modulation is used in the reverb, it may sound less obvious, or less chorused, when the Size parameter is increased.

Decreasing the Size parameter has the opposite effects:

  • A faster, tighter attack to the reverb. The input signal sounds closer to the listener.
  • A more metallic sound, in many cases. Think about the difference between a concert hall and a bathroom. Both have fairly long reverb decays, but the bathroom is far more resonant sounding.
  • Fewer discrete echoes in the reverb onset, for a smoother sound with percussion.
  • Stronger modulation artifacts.

Does the Size parameter have any relationship to the physical world?

Kinda. In some cases, when the size is listed in meters, the Size parameter can be viewed as representing the longest dimension in a rectangular room. So, if the Size is at 30 meters, the virtual “room” would be a rectangle with 30 meters from front to back.

In reality, a room with a front-to-back dimension of 30 meters will almost always sound far richer than an algorithmic reverb with a Size of 30 meters. This has to do with the resonance density of the room, which is a pretty esoteric topic that I will tackle in a future blog post. Suffice it to say that higher resonance densities sound smoother, and digital algorithmic reverbs are hard pressed to achieve the resonance density of a fairly small room, to say nothing of a concert hall.

The same can be said for Size measurements in cubic meters. In at least one notable hardware “room simulator,” the Size settings go up by orders of magnitude: 10 m3, 100 m3, 1000 m3, all the way up to an impressive 1,000,000 m3. In reality, each increase in the Size parameter results in a doubling of the internal delay lengths. This will result in higher modal densities, but to nowhere near the extent that the Size in cubic meters would suggest.

Any recommended tricks for setting the Size setting?

The answer for this sort of question will always be “set it by ear, to your own tastes, so that it fits the music you are working on.” However, I can offer a few hints:

  • For a richer reverb sound, set the Size as big as you can get away with, until either the attack is too slow or you start hearing objectionable grain. Once your reach this point, turn the Size down to a slightly lower value, until the grain goes away.
  • For sounds that have slow attacks without prominent transients (such as pads, orchestral, some vocals), feel free to crank the Size way up.
  • Percussion usually needs a somewhat smaller Size in order to not sound chattery.
  • If you have a really short reverb decay time, you might want to turn the Size down, so that you have maximum echo density during the audible part of the decay.
  • Very small Size settings are useful for special effects, and very metallic “oil tank” sounds, but aren’t normally that pleasant to hear.
  • For a more chorused decay, turn the Size down a bit.
  • Increasing the modulation rate/depth in reverbs with smaller Size settings will reduce some of the metallic coloration. This is why the EMT250 has such pronounced chorusing – the modulation was used to cover up the small amount of delay memory used in the algorithm, which essentially corresponds to a small Size setting.

Questions? Have some favorite reverb Size tricks you want to share? Leave a comment below!

About the author:

Sean Costello is the "algorithmic reverb plugin wizard" [citation needed] at Valhalla DSP.

Comment

  1. Thanks, Sean. I always love to learn more about reverbs.

    I’m still chasing that Capitol/Columbia/Abbey Rd chamber sound, but Valhalla Plate gets me closest so far.

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