An example by the numbers
As an example I'd like to show you how to create a reverb for small club with a band.
Let's see what we have to do with parameters in the reverb fx in sample editors. First we determine some basics about the room we want to simulate.
Our room (the club) is about eight meters on all sides (for simplicity) and three meters high. The band will be playing no more than four meters away from us. The room volume will be about 200 cubic meters.
This means that the DIRECT SOUND will get to you within about 11 ms (milliseconds). This is the amount of time we'll need to take off the other values.
The first EARLY REFLECTIONS (off the left and right walls) travel around nine meters before reaching you, so they'll get to your ears about 15 ms later! (9 meters at 343 meters/sec -> 26 ms minus the 11 ms the DIRECT SOUND takes to travel to your ears).
I'm not taking the floor into account because of the obstacles, such as your own legs and a table, that prevent reflections of sound from the band from reaching you. It is also probable that your sitting close to a wall and EARLY REFLECTION time may drop considerably. Experiment and listen very carefully.
The reason I'm deducting 11 ms from the 26 ms is that in a sample editor we already have the DIRECT SOUND. In Cool Edit an EARLY REFLECTIONS parameter doesn't exist. In Soundforge however there are a few ER times to choose from. We choose whatever is closest to 15 ms. Freeverb unfortunately does not have an Early Reflections feature.
Please note that the timing of the EARLY REFLECTIONS are defined by the rooms characteristics such as shape and size. The sound colour of the EARLY REFLECTIONS is defined by the surfaces in the room.These are parameters that are available to professional reverbs only (hard- or software), so don't worry about not finding that stuff in great detail in either Soundforge's, CoolEditPro's or plugins of other editors.
The PRE-DELAY and REVERB TIME depend on more than just room size. Wall and floor material, as well as anything else that reflects, disperses and dampens sound will influence the reverb in quite a few ways.
Our club has lots of wood on it's walls and floor and people are sitting at tables and the air's probably filled with a little smoke (except in California :).
The REVERB TIME, a parameter found in almost all plugins, should be set to no more than one second. In small, crowded rooms where little REVERB occurs it is quite important to set the EARLY REFLECTIONS right. Experiment with the reverb time keep it lower than 1.2 seconds and above 0.7 seconds. Freeverb puts all this information in to the SIZE parameter.
The PRE-DELAY can be set to 30 ms or more. Larger rooms will develop REVERB later since the reflecting sound will travel a while before the reflections become hard to identify but it also depends on the reflecting materials. Freeverb once again doesn't know any Predelays, but since you're reading this to learn how things work, it's still worth spelling out.
Both Cool Edit and Soundforge have parameters referring to the DENSITY of the REVERB part of the sound. Materials such as polished marble will reflect the sound very well and disperse the sound very little. Wood disperses the sound a lot and a carpet practically swallows a large chunk of it. For our Club we need to set the density high since our material disperses the sound a lot(humans,wood and obstacles). No parameter like that in Freeverb and yet it sounds great. It's easy to use as well, so I don't really mind when using it.
Higher frequencies are swallowed a lot faster than low frequencies. Many reverb algorithms refer to this in some form or another. Cool Edit has the 'High Frequency Absorption Time' as a parameter for this. Sound Forge gives you a choice, whether to do this at all for both low and high frequencies and even lets you set them but doesn't provide any time parameters. Professional Reverb hardware such as Lexicon PCM 70,80&90 let you you control frequency and time of this, for low and high frequencies. Freeverb has the DAMPEN parameter for this.
This can effectively add to room's liveliness. A room full of people will absorb high frequencies a lot faster than an empty room, in which only the materials would make the difference, so in Cool Edit we'll set the 'High Frequency Absorbtion Time' very low, since we're in a crowded club. For Soundforge activate the 'Attenuate high frequencies above' box and set the frequency parameter to around 2000-2500 Hz. Experiment a bit. The higher this frequency and the longer the Absorbtion Time parameter in Cool Edit, the emptier and and colder your room will seem. In small rooms this can cause the room to sound very metallic. Sewer pipes and oil pipelines e.g.
The Reverb EQs are the final processing stage and can change the sound dramatically. These Hishelf and Lowshelf EQs are found in almost ANY Reverb plugin and hardware unit. Freeverb has both in form of Hipass and Lowpass filters. These are not EQs. The parameters change the target frequencies of the filters. Again, listen.
The last thing you have to do is set the balance between the WET signal and your original DRY signal. Here you can do as you please but remember that only very smoothed hard surfaces in big cavernous space create very loud reverbs. A church might do that if there aren't a big number of people and wooden benches in there, but a club doesn't :). Remember that in Audacity it is smarter to DUPLICATE the part you wish to add reverb to, and run the effect over that duplicate. The volume of that reverbed material is easier to control, so set the WET parameter in Freeverb to 0dB (-&rt;100%) and the DRY parameter to -endless(->0% left most slider position).
So when you create your next 'soon-to-be-the-hit' song or want to put things in perspective, be sure to check the possibilities of adding dimension and scope to your material through clever use of reverbs. Put your snare to the front, the piano a little to the back, and the sax just a little in front of the drums. Experiment. With these basics you'll be able to get better results in less time.
Btw, Snare always gets reverb. How much and what kind up to you, but it's generally good thing. It's also important to decide whether you're trying to simulate a real live band or doing a multitrack sound, which boasts all kinds of nice ideas, like doubling(another take of the same thing on top of the first take), extreme panning and in general NOT reality :).
Dry versus Wet
Have you heard of those silent rooms, where they test speakers and microphones ? They're great if you don't happen to be inside of one. After a few minutes you hear the blood in your ears roar like an ocean. You hear only your inner voice when you speak. The room swallows almost everything else. Most people can't stand being in a room like this for more than 10-15 minutes. I am told that this is very different to wearing ear plugs. Those only attenuate sound from the outside. A silent room kills it completely.
This room is horrible to listen to, because it basically features no room reverberation, i.e. it doesn't reflect anything at all. It doesn't reveal any information about its size or surface composition.
You may be surprised to know that many vocals are actually recorded in similar environments. Vocal booths are little rooms, in which the walls reflect sound as little as possible. During mixing, digital reverbs are used to create a virtual space.
Audacity for Windows and MacOS9&X includes the VST plugin Freeverb, which is one fine reverb, and ideally suited to take your first steps with digital reverbs. It features simple controls that require little explanation.
For details about Freeverb, check out the effects menu page. For information on how digital reverbs work and what reverb is, check out this page of this manual.
Keeping effects on seperate tracks
You shouldn't use reverbs on original audio tracks. First duplicate the audio and use the reverb on that duplicate. The reverb should be set to output 100% WET (i.e. 100% effect signal and 0% of the original signal). That way, you can control how much reverb should make it in to the final mix, right up until the last minute.
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