Reverb, Delay and Echo
Echo was a beautiful nymph in Greek mythology with a musical voice who was employed by Zeus to distract Hera with incessant babbling, gibbering and gossip while he embarked on sexual adventures with his many paramours unhindered.
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Hera, driven half insane by her inane jabbering, lost patience, took the power of speech away from Echo and removed her from Olympus. All Echo could do after this was to repeat the last words that anyone had said to her. After falling in love and being spurned by Narcissus, she rejected the advances of Pan, who was willing to overlook her affliction, and who in a fit of pique smashed her into tiny pieces and scattered her all over the world. She can now be heard by anyone who raises their voice.
Reverb is essentially echo where the reflections are so close together that the results are perceived as a single sound. Reverberations, simulated or otherwise, are an integral part in the recording process, in live performance and also in our very perception of our surroundings. A few years ago, I had occasion to be in a 97% anechoic chamber at Paisley University’s Ayr campus, and I can testify that it does not necessarily feel like a friendly nor welcoming place to be. Your eyes tell your brain that you’re standing in a room that is fifteen feet by ten, while your ears are telling the brain that you’re in a coffin with two inches of space around you. The results can feel almost nausea inducing to someone unfamiliar with them. It takes a little time to become acclimatised to this environment.
In a mix or a live performance, reverb will be used to make a vocal or instrumental performance sound more polished and to fit nicely into the mix giving an impression of depth and space. Delays and echoes can be used to give more life to parts or tracks in a mix, or to create a dramatic stereo image. Used in conjunction with panning, delays can be used to help create artificial Doppler effects, one of my favourite techniques for adding a bit of theatrics to a mix. Used cleverly in a mix, delay can be subtle enough that it is not obvious when swallowed by the rest of the instruments and be used just to change the feel of a track by giving it life and space, or it can simply over used to give a dramatic edge to an instrumental part.
Reverb and echo are often associated with religious or spiritual connotations. Churches have been built since the middle ages with dramatic acoustic properties in mind. Religious Choirs and Orchestras tend to perform in large echoic chambers with reflective surfaces. In the 1980’s television series “Robin Of Sherwood” delay and large reverberations were employed to give Herne the Hunter’s voice ethereal power and to give a demonic and sinister edge to some of the evil characters like the devil worshiping Baron de Beleme as he summoned the spirit Aziel.
Echo appears to have been employed for religious reasons even before the construction of the dramatic medieval Cathedrals. The Aztecs, with certain of their pyramids, seemingly designed buildings to use reflections in creating sound effects. If you clap your hands in front of the 1,100 year old Temple of Kukulcan, in the ancient Mayan city of Chichen Itza and the pyramid answers in the voice of the sacred quetzal bird.
In the 20th Century, with the dramatic rise of recorded music in popular culture, reverberations have been simulated using tiled rooms, springs, plates with transducers attached to them and now in the modern era digital computer algorithms. The main advantages of the latter are two fold and diametrically opposite to each other.
A digital reverb can be used to produce far more realistic simulations than springs or plates, with total user control over the pre delay time, the decay, the colour of the reverberations, and the diffusion. In fact, with digital technology, real rooms can be modeled using convolving reverbs that work with impulse responses that are generated by recording staccato broad band signals and the corresponding reflections, which can then be used to model the effects of the same room on other signals. The other and opposite advantage of digital reverb is its ability to create rooms that could not exist in real life. Rooms with virtually no pre delay or with infinitely long decay times can be generated with digital reverbs.
Electronic Reverb Settings
The main settings on a digital reverb or reverb plugin are predelay, size, reverb time, colour, damping and a setting for wet / dry mix.
The predelay determines how far the sound source is from the walls of the room. This has the subjective effect of creating depth, and long predelays of fifty to sixty five milliseconds are often used to wash vocals and make them fit better in a mix. Sound travels at one thousand feet per second through air, so a fifty millisecond predelay gives the effect of placing a sound source fifty feet away from the opposite wall of a room. This sounds pretty huge, but it is not unusual for concerts to take place in large concert halls or auditoriums that are considerably larger than fifty feet in length.
As you can see in the diagram below that was created using the FreeverbToo plugin with a one millisecond predelay, the sound source is placed very close to the wall. In fact, sound travels one foot in a millisecond, so this represents a sound source a foot away from the wall of the room opposite the sound source. Small predelays would be used in generating a reverb that is close, to have a mix element sound like it’s in the foreground of the sound field.
In the second example, a predelay of fifty milliseconds has been selected, and the sound source in the diagram is now further away from the wall. A fifty millisecond predelay translates into fifty feet. This kind of predelay setting would be used in generating a reverb with depth, possibly to simulate the reverb of a large hall on a dry vocal track. As a matter of fact, one would be hard pushed to find any recorded music from the 20th or 21st century that did not have some kind of reverb on the vocal tracks, whether from a real room or some kind of simulation.
Quite simply and as one would expect, room size determines the size of the room that is being simulated. To create a huge spatial effect on a mix element, select a large room size. To keep things tight and close, select a smaller room size.
We’re treading into pretty subjective territory here. Large room sizes could be used to create ethereal effects on vocals, strings, and in fact on various mix elements. I myself have used artificial large room reverbs to create an artificial orchestra that was multitracked across over a hundred tracks by a single violinist to simulate the feel of a huge orchestra in an auditorium. Small room sizes would be used to give a more natural feel on a mix element whereas large room sizes give an impression of space and power.
Damping can be used to simulate coverings on walls and objects in a room that absorb or diffuse sound. For example, it stands to reason that the smooth tiled wall at the local swimming baths will reflect sound more efficiently than a wallpapered stud partition that you would find in a house.
It seems unlikely to me that an engineer working on a studio multitrack mixdown of a song would worry about checking up on the reflective index of cement walls or wooden panels and trying to set a reverb to match on his tracks, he would be more inclined to manipulate the damping control until he found the sound he liked, but this kind of idea may be more important for an engineer wishing to create sound effects with a view to realism, for example in effects for radio or television.
It stands to reason that not all surfaces or objects will necessarily reflect sound equally at all frequencies. The colour control on the reverb unit or plugin can adjust the frequency spectrum of the reflections being simulated. Alternatively, the output of the reverb unit could be patched through an equalizer before being returned through the mixing desk. Using lower frequency values for colour will generate a “warmer” feeling reverb, while using higher frequency values will generate a “brighter” feel.
Wet And Dry Mix
It stands to reason that when standing in any acoustic space, one will hear sound waves directly from the source as well as reflections from the ambient surroundings. The levels of these can be adjusted in an electronic reverb by changing the wet and dry mix. In an anechoic chamber, one will hear the dry source almost exclusively as there are close to zero reflections, whereas in a large wood paneled hall, one would hear a lot of reflected sound.
Elements in a mix, especially things like overdriven guitars, have a habit of swallowing up reverb, which can be compensated for by making the reverb wetter. In modern music production, the level of wet reverb will typically be considerably lower than the dry signal, as the reverb tends to be more often used to add spaciousness to a mix than purely as a special effect. One thing to watch for when setting these levels is that the mix settings don’t cause the sample to clip.
The Reverb time, or RT60 of a room is a measure of the length of time, usually in milliseconds, from when the initial sound reflections are set up to when they are attenuated by sixty decibels. This is simulated in a digital reverb and can be anywhere between close to zero and infinity. This is of course not possible in a real room, where the reverb time will be dependent on how big the room is and how reflective the walls are. It is common practice in modern production to have reverbs that can be large but are tightly gated in terms of the time domain to give a spatial effect which is still kept tight and controlled. This is particularly noticeable on percussive instruments like snare drums. Properly controlled reverb times are instrumental in keeping a mix tempo based, and stopping it from sounding sloppy and wet.
In the days before the era of the electronic reverb, plate reverbs were used to simulate spatial sounds in music. Listening to music recorded in the seventies, it is obvious that a lot of the engineers who tuned these devices were immensely skilled in using them.
Commercial plate units use piezoelectric pickups or accelerometers attached to a metal plate which is bolted onto a frame. These are basically contact mic / pickups that pick up vibrations in the plate set up by a driver that carries the dry sound to the plate, as seen below.
The level of reverb on a plate is set by having the dry signal on one tape return and the wet signal on another. The levels can be adjusted using faders on the mixer. Tuning plate reverbs is accomplished by adjusting the lugs that hold the plate in place so they are all equally tensioned. It is important in doing this to listen for flutter echoes or beats, which are similar to the sound modulation set up by playing two slightly out of tune guitar strings simultaneously, and eliminating them. Improperly tuned plate reverbs can give an unpleasant and unnatural metallic sound.
Timing A Delay
In order to time a delay to land on the quarter beat, there is a very simple equation that can be employed. Simply divide sixty thousand by the beats per minute of the song and you have, in a four four time signature, the number of milliseconds in every quarter beat. If you want an eighth beat delay, simply divide this number by two, for a half beat delay multiply by two. For a sixteenth beat, a full beat (semibreve), or anything else, apply the same principles, very simple maths.
If you don’t know the beats per minute tempo of the song because it hasn’t been tracked to a click, then it’s time to either download a tap plugin (last I checked a Google search for the Analog X tap will get you one), or get the stop watch out and do some counting, but generally speaking, delay is more effective in recordings that have been tracked accurately to a metronome.
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About Graeme Young
Graeme Young is a sound engineer based in the South of Scotland, starting his career after being presented with a Yamaha MD8 in the late 1990’s by a friend who had despaired of figuring out how “the damned thing” worked. Brimming with enthusiasm as he learned his way around his new toy, he immediately set to work with gusto, creating some of the most abominable sound recordings of musical doodling ever committed to tape.
Nevertheless, the heady times of fun and friendship that were built up in the early days convinced Graeme to go back to college and expand his knowledge and skill set, meeting contacts and learning the tradesman’s tricks from industry professionals. In the meantime student loans were spent on studio equipment to expand on the trusty MD8 while the O2R96 and the old StudioMaster at the college provided experience of working in both the analogue and digital domains.
Now, Graeme has gained years of industry experience working on a number of studio recordings and location recordings with professional musicians and in directing and editing video projects for professionals in various fields. Graeme has fronted two bands, the now discontinued Popping666Cherries alongside Gwen Smith, who had fifteen minutes of fame on the X-Factor before being told by Simon Cowell that she would “never do anything” and now his own Moonstruck Project, with a loose collaboration of musical friends.
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