I have received a lot of requests for a Basics series on effects. We all know that effects are the key to many of the sounds we love but many times that understanding stops at the name of the effect and a general idea of what it does. In this occasional series we will cover all the major effects and then some. Our review will cover basic uses and the most common control elements for each type of effect. I’m hoping to hit the high yield topics first and there’s no better way to lead off than with the effect of our times: Reverb.
You Know It When You Hear It
It helps to start our conversation by defining what we are talking about. At its most basic reverb is an effect that gives a sense of space. In other words, reverb tricks our brain into thinking that the sound we are hearing is happening in some sort of physical space other than the one between our ears. What sorts of changes in the sound are happening to create that illusion? Generally reverb algorithms have a few things in common:
- They generate many echoes of the initial signal. The specific sound of the echoes depends on the method. In a room sound emanates from the sound source, hits the walls and continues on to the listener. More than anything else these echoes contribute to a sense of space.
Reverbs create both early reflections which are distinct echoes of the source, and diffuse echoes where individual echoes are lost in a wash of hundreds or thousands of echoes all starting at slightly different times and re-echoing off other walls. Diffusion separates reverb from its popular cousin – delay.
Many reverb units roll-off or attenuate the high frequency content of these echoes. In air high frequencies are attenuated fairly quickly over distance. This also contributes to a more realistic sense of space.
Major Types of Reverb
In the early days of recording reverb was hard to come by. You either had to record in a room with natural reverb or pipe your sound into another space (like a reverb chamber below the studio) and record that. Needless to say this is not time or space efficient. It didn’t take long for engineers to come up with clever ways to fake a reverb sound.
Spring reverb was the first type of simulated reverb with the first patent issued to the Hammond cooperation in 1939. The technique involves coupling a driver to one end of a spring and a transducer to the other end. The signal from the driver causes the spring to vibrate; the transducer picks up that vibration and returns it as an audio signal. The characteristics of the reverb are determined by the tension, composition and length of the spring. In my opinion spring reverb tends to be a bit more indistinct and brighter than plate reverb.
Plate reverb was the next innovation in artificial acoustic space. The technique is similar to spring reverb where the signal is sent through a driver coupled to one end of a large sheet metal plate with a pickup at the other end. The character of the reverb is determined by the size and composition of the plate.
We have journeyed through the 1930’s to the 70’s. So far artificial reverb has been expensive OR of comparably poor quality. Live reverb was really limited to spring reverb or the room you were in. In the 1980’s everything changed with the advent of the microprocessor.
Algorithmic reverb describes a method whereby an audio signal is digitized and then the reverb reflections and tail are created in a microprocessor. The 1980’s were defined musically by a boom in availability of comparably high quality digital reverb units that used this method. As a result you can hear globs of reverb all over just about everything recorded in the 80’s. We would probably not think as much of many of the reverbs from that era but at the time they were much better and more available than the electromechanical reverbs discussed above. Early digital reverbs also employed a lot of frequency modulation (chorus) to mask artifacts created by their underpowered (from our vantage point) processors.
In the 1990s the personal computer and digital audio workstations became the recording medium of choice. The increasing horsepower of computers made impulse modeling possible. This reverb method takes a sampled audio signal from a space to determine the reverb signature of that space. The audio signal is then convolved into that space based on this acoustic signature providing a reverb signal very similar to the physical space that was sampled. Many people believe that such Convolution/Impulse Response reverb algorithms provide some of the most natural reverb sounds at the expense of a lot of processing horsepower.
Reverb units tend to share the same types of controls however the particular name may change a bit. Some reverb units may not give you access to all of these controls.
- Pre-delay: Controls the interval between the dry source signal and the first early reflections. In a real room there is always a delay between the original signal and the reflections from that signal.
- Early Reflections: Controls the relative level of the early reflections. A high level simulates a room with very reflective surfaces near the listener. A low level simulates a room with more distant diffusing surfaces.
- Room Size: Controls the overall reverb time. In some units this will also be the main way to control the character and timing of early reflections.
- Room Shape: Controls the number of reflecting surfaces which in turn affects the character and timing of Early Reflections. Few surfaces generating reflections cause the Early Reflections to be more distinct.
- Diffusion: Controls the rate at which the reverb tail achieves maximum density.
- Density: Controls the smoothness and character of the reverb tail. Low levels have a sparser sounding reverb tail (think of a room with absorption placed in patches all over) and high levels create a fuller reverb tail (think of a random shaped concrete room with metal plates hanging from the ceiling all over).
- High Frequency Damping (High Cut) & Ratio: Controls the frequency at which the damping takes effect. The damping ratio itself controls how fast the high end decays relative to the overall Reverb Time (decay time). In a real room high frequencies decay faster (ratio less than 1).
- High Frequency Gain: Controls the frequency and gain reduction for the high frequency content of the reverb output.
- Crossover: The frequency that separates the low frequency processing from the high frequency processing.
- Low Frequency Damping (Low Cut) & Ratio: Controls the frequency at which the low end damping takes effect. The damping ratio itself controls how fast the low end decays relative to the overall Reverb Time (decay time). In a real room the low end has a slower decay (ratios over 1).
- Low Frequency Gain: Increasing the damping (or decreasing the gain) will reduce the low frequency content of the reverb signal.
- Reverb Time (Decay Time): Controls how long it takes for the reverb signal to decay to zero. The maximum setting may be limited by the specific type of reverb chosen.
- Mix (Dry and Wet): Controls the ratio of dry (unaffected) signal to the wet (reverb) signal. In single slider “Mix” controls one end is all dry signal and one end is all reverb (usually 100% is all reverb). Some units have a level control for each type of signal.
- Modulation Rate: The speed of the chorus effect. Used to blur the reverb tail.
- Modulation Depth: The amount of the modulation effect incorporated into the reverb tail (think “Mix” control for the modulation effect).
Tips and Tricks
Use PreDelay to define or blur the source
PreDelay can give your source sound some room to breathe. Increasing the pre delay will start the actual reverb later after the source. This is helpful for percussive sources like piano or rhodes. Decreasing the predelay moves the reverb towards the source and can be useful for creating the nice washy sound bed for a pad.
Bigger isn’t always better
You can think of the room size as a container you have to fill up with sound – once it’s full you’re getting the maximum amount of ‘verb out of that room. If you’re looking for a super-dense full reverb a smaller diffuse room might give you what you’re looking for, or maybe a plate would be better.
Modulation = Color
Modulation is a big component of shimmer-type reverb. Try using more when you are trying for a reverb that is more of an effect.
Different reverbs are, eh, different
It may go without saying but the algorithms driving the reverb sound in your hardware or plugin are special to that unit. Try out as many as you can, seek out those that other musicians are enjoying and try to figure out what makes them special. There’s no such thing as a bad reverb, just one you haven’t found a use for yet.
Make it unreal
I mentioned that most reverbs roll off the high end but there are lots of time that I like to keep that high end as part of a pad sound or for effect. Move the knobs the wrong way and see what happens.
That Wraps it Up…
I hope that you have learned a bit more about reverb and especially the controls that will bend it to your will. Please leave any other questions in the comments below as well as any other tips and tricks. Thanks!