About Reverberation

Reverberation occurs when sound is produced in an enclosed acoustical environment. Even outdoors, there is likely to be some level of reverberation, however subtle. The sound propagates through the air before it arrives at the listener, but the sound is also reflected when it hits walls or other objects. Due to the propagation time, these reflections arrive at the listener later than the sound from the direct path. After a certain build-up time, there are usually so many reflections that no distinct echoes are distinguishable, but rather a smoothly decaying sound.

The first few reflections, usually called early reflections, are important cues for our perception of an acoustical environment. For that reason, most digital reverberation units differentiate between early reflections and the dense late reverberation. Verberate 2 simulates both the early reflections and the dense reverberation in a way that comes extremely close to what can be measured in a real acoustical environment.

An important tool when analyzing the reverberation of real rooms is the impulse response, which can be measured by playing a very short impulsive sound (the impulse) and recording the resulting reverberation. The figures below are examples of impulse responses obtained from Acon Digital Verberate 2 as well as from a real measurement of a concert hall.

Results of an impulse response measurement of the Tokoy Hall preset in Acon Digital Verberate 2 (the first 300 milliseconds).

A measured impulse response from a real hall (the first 300 milliseconds).

So-called convolution reverbs can use these impulse response measurements to recreate the acoustical space. However, they only capture a snapshot at a specific time. Real acoustical surroundings will have slight variations due to air currents caused by temperature differences or fans. Also, performers or people moving in the audience will cause slight variations. These small variations may seem subtle, however the effect towards the end of the reverb tail will be significant, since the sound is reflected a large number of times before the reverb tail fades out. The new Vivid Hall algorithm models these random variations without artifacts like chorus effects or pitch changes, and is therefore capable of simulating reverberation of real halls with a higher degree of realism.

Dispersion Effect in Metal Plates

Mechanical plate reverbs are popular for their special sonic qualities. These vintage units produce reverb by placing a transducers on a metal plate. The powerful Decay Editor in Verberate 2 makes it easy to simulate the longer high frequency decay that is special for plate reverbs. However, unlike how sound travels in air, high frequencies travel quicker than lower frequencies in a metal plate. Verberate 2 lets you simulate this effect using the Dispersion parameter that you can set anywhere between 0% and 100% (for maximum time difference between high frequency and low frequency content).

This spectrogram shows how high frequency content arrives earlier than low frequency content when dialing in Dispersion in Verberate 2.

Swirl Effect

Vintage digital reverb units commonly use frequency modulation techniques in the feedback loop to increase echo density without adding too much resonance. Such feedback modulation is no longer required in modern algorithms, but the feedback modulation can be sonically pleasing and desirable. The Vivid Hall algorithm makes it possible to simulate the effect of feedback modulation and we call this effect Swirl.

This spectrogram shows the effect of the Swirl on a sine wave input (880 Hz). Notice how the red line broadens towards the end of the reverb tail, giving the reverb a cloud-like vintage flair.