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What is Sound Reverberation?

Reverb affects everything we hear and is common to almost every musical recording. In today’s post, find out just what sound reverberation is, how we use it, and how we can measure it.

concert hall reverberation

Reverberation surrounds us every day, and we hardly notice it. In fact, reverberation is so common to our ears that a ‘dry’ sound without reverb makes us uncomfortable.

The only time that we really take note of reverb is when we find ourselves in a large auditorium or room where the reverb becomes a rich sound that seems like a clever trick.

Guitarists make use of analog, digital or mechanical devices to use this natural effect to their advantage. Famous guitarists like Jeff Buckley and David Gilmour are renowned for their use of reverb in their music.

In today’s article we get to the bottom of reverberation. We explain what it is, how we create it, how we use it, and how we can measure it.

What is reverb?

There are many different and complicated explanations with detailed diagrams that will set your head spinning unless you are used to that sort of thing. Most of us aren’t, so here is the short explanation:

Reverb is when the sound from any source “bounces” off the surfaces in a room and the reflections of the sound reach your ears at different times. There can be thousands of reflections, all reaching your ear at a slightly different time with different amplitude (loudness). This causes a “layering” of the sound which is rich in character.

You rarely hear a sound that hasn’t been affected by reverb. You hear the direct sound straight from the source, as well as multiple reflections that have arrived at your ears after interacting with various surfaces in the physical environment that surrounds you. The effect is well illustrated in the two diagrams below.

reverb

reverb graph

As you can see in the graph above of sound energy over time, you hear a strong direct sound followed by maybe thousands of reflected sounds that decrease in energy over time.

Different surfaces reflect sound differently and will each absorb energy from the sound waves. The amount of absorption depends on the frequency of the sound too. For example, thick carpet will absorb large amounts of high frequency sound, while tiled bathroom walls will reflect these types of sound waves quite effectively. The surfaces of a room will decide the reverb characteristics of it. Imagine clapping in a bathroom compared to clapping in a recording room.

The bathroom has a long reverb time as the sound waves are reflected well. They ‘bounce’ around the room creating a long tail of reflections. The recording studio has been acoustically treated to prevent this phenomena from happening. The acoustic tiles and thick drapes absorb high frequency sound and create a shorter reverberation time that is better suited to recording music in. When recording it is preferable to add the reverb digitally in the mix-down.

The anechoic chamber

The reflections that form reverberation breathe life into the sounds we hear. This was never more apparent to me than when I spent time in an anechoic chamber. An anechoic room is designed to absorb as much reverberation as possible. It’s probably the quietest place on Earth and it’s used to test things like loudspeakers and headphones.

Spending even a few minutes in one of these rooms is very disorientating as your sense of hearing is completely impaired. You are only able to hear the direct sound as any reflections are absorbed by the acoustic panels. This means common sounds become unrecognizable. For example, clapping your hands becomes a dull “thud” rather than a loud “clap” rich in high frequencies. It’s really quite an experience and if you ever get the chance to venture into one of these rooms then I highly recommend it.

The video below highlights the differences between a reflective room and an anechoic room.

Calculating reverberation time: RT60

Reverb is magnified in larger rooms; when you’re in a large auditorium the sound goes on long after the initial sound has stopped (think about hearing music in a church or cathedral). Guitarists have found ways to replicate the effect to change and embellish the natural reverb in a room, to add more effect to their performances.

If you want to test the reverb in a room, all you have to do is stand in the middle off the room and clap and listen for sound decay.

Different rooms require different reverb characteristics. A classroom requires very little reverb, as if a room is too reverberant then it becomes difficult for us to concentrate on particular sounds and leads us to fatigue quicker. However, a concert hall is usually quite reverberant and is specially designed so that each frequency band has a specific reverberation time. Its acoustic character allows the music to flourish.

The reverberation time of a space is calculated by measuring the time it takes (in seconds) for the sound level in a room to decay (reduce) by 60dB.

rt60 time

This is done in narrow frequency bands of an octave or a 1/3 of an octave, as reverb time changes a lot with frequency.

The sound used is very particular too. We need to use uninterrupted pink noise or a loud impulse. Also, this must played through an omnidirectional sound source such as a dodecahedron speaker at a sound level that is about 75dB (15dB headroom) above the ambient noise level in the room (usually the ambient noise is around 45dB).

An SPL meter needs to be used to measure the sound levels, and a stopwatch can be used to measure the RT60 times. A good sound meter might well have this capability built in however. It’s really important that you take precautions to protect your ears too, as things might get loud!

Acoustic Chambers

Back in the early days, the only way to add reverb to your playing was through recording. This was achieved by strategically placing microphones to capture the sound for more pronounced reverb. Playing live was much more of a challenge and you had to adapt quickly. These days, we have a wide array of reverb replicators such as multi-effect boards, stomp boxes and rack mount units.

piano concert

Mechanical reverb

The advent of mechanical reverb makes the lives of many guitarists much easier and also enhances the sound of many musical performances. These days, most amps have built-in spring reverbs. Spring reverb electrically sends the sound through springs. It’s a really cool reverb effect.

This produces a unique and slightly splashy sound that is popular in surf music. This doesn’t always have to be the case though, and the splashy effect can be combatted by playing the reverb at a lower level. Some amps, like Fender amps, are renowned for their distinct sound and range. This means that all you need is a decent amp and you can use reverb to your advantage.

It wasn’t always this easy, since earlier mechanical reverb apparatuses were completely unrecognizable to what we use today. One of the earliest ways of mimicking reverb was the plate reverb.

This device consisted of a 4’ by 8’ sheet of metal stretched extremely tight over a frame while a sound driver was attached on one end to make the plate vibrate; the waves would then travel through the room and be picked up by strategically placed microphones.

These devices posed a number or problems since they weren’t easy to transport and the microphones picked up a myriad of different sounds, requiring an isolated and empty room.

Digital Reverb

This type of reverb is a huge advantage for guitarists and almost anyone can use it. When properly applied, this technique can enhance the tone of your song. For example, Jeff Buckley used digital reverb in his cover of Leonard Cohen’s Hallelujah. His cover is almost as famous as the original and has been praised for its sense of loneliness and intimacy.

guitar effects pedals

Rack mount units, stomp boxes, and multi-effect pedals enable this effect to be used easily by guitarists. These devices can sound incredibly realistic since they imitate reverb used in actual rooms. Gone are the days when musicians had to struggle to adapt and when reverb was a matter of luck or reserved for famous musicians.

Incorporate reverb into your sound

Reverb is something that a guitarist needs. It fills out your sound and combats a dry room. It can be easy to use the effect, but there are a few basic guidelines that are worth considering and applying.

Reverb devices need to be as close to your pedal chain and in your amp’s effects loops if possible. This is essential if you have other effects since the reverb will also be affected. For example, if you use a reverb pedal before distortion, then the reverb will be distorted and the purpose of both will be defeated.

If your reverb is in the amp’s effect change, then you safely can use your reverb without any interference from the distortion or EQ; the effects loop is after the preamp in the signal chain. Most reverbs have a mix knob; this allows you to blend your input and reverb (input is dry while reverb is wet) and control the volume with regards to your guitar’s tone.

A good DAW can apply natural sounding reverb while recording or in the mix.

If you make it too high, it will sound as though you’re playing in a cavern and this will be extremely unpleasant, but if you manage to get it just right, you can have a perfectly balanced blend that will do wonders for your sound.

Conclusion

Reverb is a natural gift that fills out a sound and keeps it from becoming dry and unpleasant. It is a tool that all guitarists need to use if they want a more dynamic sound that enhances their skill and talent. Reverb isn’t a complicated concept; in fact, it is easy to master.

If you’re worried about external noise affecting your recording set-up, then check out our guide to soundproofing.

We’ve also got an awesome guide on the top studio monitors for every budget.

Our latest post recommending the perfect gifts for musicians is a must read too!

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