Originally Posted by: PaoloT 
... the Density parameter in algorithmic reverbs (like MIRacle) should always be increased as much as possible, or there are cases when a lower density can be desirable? My first impression is that more density equals a smoother tail, therefore a better reverb. But is it really so?...
Paolo
Dear Paolo
This is not an embarrassing question, it is a good one. Unfortunately, my answer is not necessarily valid for all reverb plug-ins, because it depends very much on what the respective manufacturer changes behind the parameter "Density"...
Maybe others are also interested and I explain in general how the reverb is created:
In general, reverb is the sum of reflections beside the sound which reaches us directly. In reality, the direct sound from an instrument reaches the listener first. If the instrument plays far away (e.g. in a church), the first reflected sound waves reach the listener soon after the direct sounds. This is because the first reflected sound did not have to travel much further than the direct sound. If, on the other hand, an instrument plays very close to the listener, it takes quite a long time for the first reflections to arrive after the direct sound (some milliseconds >> 3,3ms/m) . The walls (ceiling) closest to the listener are responsible for these first reflections. These first reflections are called early reflections (ER). The parameter Pre-Delay usually sets the time between direct sound and these first ERs. By the way, our brain evaluates these ERs. It uses them to gain information about the distance and direction of the playing instrument in relation to our position.
Now more and more reflections arrive at us as listeners. They mix together to form the so-called tail. How many of these different reflections are to be formed is normally set with the value "Density". A room that is shaped like a cuboid and then with a "flat" surface produces fewer and also less different reflections than a room with many angled corners and with different surfaces. Reflections in the latter room are denser in number and variation. Rooms with smooth surfaces, however, can again result in long-lasting fading, while rooms with many corners and different surfaces are more likely to fade...
So the density parameter mostly simulates these space and surface things which then result in more or less reflections. More different reflections can therefore result in a denser, fatter or fuller tail. This is perhaps not always what is wanted.
On the other hand, it is sometimes disturbing, especially with percussive instruments, if the individual reflections (echoes) are heard instead of reverb when there is "too little density". So too much density can lead to a too "thick" reverberation, too little density can mean audible echoes. Therefore, there is no general recipe for how much density to set. Especially not, because we do not know exactly what is adjusted behind the "Density" control of the different manufacturers...
Large Hall - sometime not enough density / Long Dense Tail - always enough density (no echos)
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By the way, in some churches, but also in gymnasiums, community halls or other halls, you can hear these echoes in reality when you clap your hands on stage or anywhere in the room. Depending on the music, however, this is no longer so disturbing...
For more Information about Reverb go to About Reverbs or to all the other points on the subject of reverberation.
All the best
Beat