Reverb

View of Manuel Haible, Heiko Wommelsdorf and Georg Werner’s 2010 installation, ‘Klanglumineszenz’. Photography: Roman März / Singuhr Hoergalerie

'The only technical things I know are treble, volume and reverb.' Johnny Thunders - New York Dolls

What is Reverb?

Reverberation, in psychoacoustics and acoustics, is a persistence of sound after the sound is produced.

 Valente, Michael; Holly Hosford-Dunn; Ross J. Roeser (2008). Audiology. Thieme. pp. 425–426. ISBN 978-1-58890-520-8.

All the time, in every space that we’re in, reverb is always there. Reverb is the way sound interacts with the physical spaces that we’re in. It affects a sound after it has stopped sounding. If you hit a drum in a room, what you hear is a mixture of the original sound and the reverb, which is reflected and diffused versions of the same sound, bouncing back to you from the surfaces in the room. Reverb is amazing and it's no wonder that it has become one of the most popular and interesting audio effects of all time.

Wave-based sound propagation modeling - Brian Hamilton 

In order to understand reverb as an effect, and to have full control over it, we must first consider it as a natural phenomenon. 

 

https://heroic.academy/your-guide-to-everything-reverb/

                                                 

Using the images above, we can see how the perception of a sound in a space is split in to phases (simplified slightly here, as we are primarily interested in how to control the effect in our recording and mixing practices):

• Direct sound, the green line showing sound travelling directly from the source to the ears (or microphone). 

• Early Reflections (indicated by the orange lines) are the first reflections to arrive at the ears, probably after reflecting off only one or two surfaces, perhaps 5-100ms after the original source. The early reflections supply information to the brain about the size and characteristics of the room. At least that is the conventional thinking... Companies like Lexicon, who make some of the best reverb and delay units argue that early reflections are a purely academic concept that doesn't fully describe the process of reverb in a real space. Basically, they argue that reverb is not split in to distinct phases but that the process is continuous, and furthermore that you may be hearing some second, third and fourth order reflections before you've heard the first reflection off the furthest wall! Even so, it's important you understand the concept of early reflections if you are to get the most out of reverb units made by all manufacturers.

• Pre-delay, this actually occurs before the early reflections. It is the time between the direct sound and the first early reflections. Larger rooms = longer pre-delay as the sound will take longer to reflect from the closest surfaces.

• Reverb time, otherwise known as RT₆₀ or Decay time. This is the amount of time it takes for the signal to drop by 60dB. In a physical space, this is affected by a number of variables, including; size, absorption values of materials (how well they soak up sound), shape of surfaces etc. In simple terms, it is how long it takes for the sound to fade away. (Note, the blue line in the picture above represents the late reflections and these are the last to fade.)

Finally, to get the most from your reverb plugins and hardware units, it's useful to understand a couple of other terms:

• Diffusion relates to the way the sound breaks up when it hits a surface. Low diffusion values would indicate (basically) less complex shapes on the surfaces of a room, resulting in more defined individual reflections. Click on the gif below to be redirected to a snare recording, first with a low diffusion setting applied and again with a high diffusion setting (from the isotope SoundCloud page). 

• Damping is the control over the absorption level of high frequencies by the reverb unit. This has obvious practical uses, inspired by the fact that certain spaces absorb high frequencies better than others. For example, an empty hall will have less absorption of high frequencies than a hall full of people.  

Types of Reverb Effect
The Original Solution – 'Echo' Chambers

https://www.sunsetsound.com/wp-content/uploads/2012/12/Sunset-Sound.pdf

Before anyone had invented newfangled solutions to creating artificial reverb effects, the only way to do it was to use a reverb (or echo) chamber. This was (and still is!) done by sending a copy of some 'dry' recorded material to a speaker in another room with particularly pleasing reverb (sometimes studios would use their tiled toilets for this task).  The signal would be played in the reverberant space, then be recorded using a mic or mics in the room, before being sent back and mixed with the original signal. As many studios in the 40s, 50s and 60s would only have access to one chamber, these spaces featured on thousands of recordings and became stars in their own right! 

According to Reverb.com, in this article which covers all of the above and gives some great examples of classic reverb chambers, 'Bill Putnam is often credited with the first recorded use of artificial reverb. In 1947, Putnam used his Chicago studio's bathroom as a makeshift echo chamber on The Harmonicats' "Peg o' My Heart," an instrumental ballad from 1912 covered by a trio of harmonica players.'

Analogue Reverbs

Not all studios had access to a reverb chamber so engineers started to work on ideas to create artificial reverb effects. Let's take a look at the two main types; spring reverb and plate reverb.

Spring Reverb 

A spring tank - https://anasounds.com/analog-spring-reverb-how-it-works/

Spring Reverb is a simple but highly effective idea. Spring reverbs work by sending your signal through moving springs; the vibrations in the springs cause the reverberation. At either end of the springs is a transducer which causes the springs to move. What is especially brilliant about this solution is that spring reverbs are really compact. This means they could easily be added to guitar amplifiers etc. providing a highly portable reverb effect.

How do they sound? Well, whereas reverbs from natural spaces reflect sounds in highly complex patterns, analogue reverbs are more two dimensional. That's not to say they sound worse, far from it, just different. See the video below for a demonstration. 

Plate Reverb 

EMT 140 Plate Reverb - https://www.soundonsound.com/techniques/choosing-right-reverb

Plate reverb is another brilliant solution to the reverb problem. It works by suspending a large 'plate' or sheet of steel in a frame, usually held in place under tension by springs. The plate is then fed a signal via a transducer attached directly to the metal. This vibrates the metal and causes reverb. The reverberated signal is then captured via a contact microphone  and becomes your output signal. 

How do they sound? Plate reverbs have a brighter but still highly synthetic sound. See the video below for a demonstration.

Digital Reverbs 

With the emergence of digital technology came a revolution in how reverb effects could be created. Using computers, programmers and engineers were now able to synthesise reverbs in a whole host of new ways, without the need for rooms, chambers, springs or plates. These can be subcategorised into two main types; convolution reverb and algorithmic reverb. 

Convolution/ IR Reverb

Altiverb by Audio Ease

Convolution reverb is a really interesting concept. Reverb profiles are recorded from individual spaces, which can then be applied to audio signals via an instance of a plug-in (like altiverb, pictured above). The process of recording a reverb profile is reasonably simple to do (the software does all of the hard work!). It relies on the recording of an Impulse Response (IR) in the given space. This is usually a tone frequency sweep played back through a PA system and recorded with cardioid or omnidirectional microphones. The resulting recording (sweep response) is then loaded into a dedicated plugin that converts the information into a reverb preset, which can be applied to any audio file or signal running through the processor. See this article by ProTools Expert for a detailed description of the process. How do they sound? If everything has gone to plan, they sound like the original space! This means you can record your instrument, then make it sound like it's in the Royal Albert Hall, or the oil tanks in Invergordon at the click of a mouse. 

Algorithmic Reverb

The EMT 250 Electronic Reverberator

In 1976, the first ever digital reverb unit was released, the EMT 250. This unit, as with all algorithmic reverb hardware and software plugins that followed, used mathematic algorithms to create the effect of reverb. There are some big advantages to creating reverb like this, mainly that these algorithms are less intensive on the CPU of your machine. When the EMT 250 was created, there was only 16K memory chips available, so it had to be efficient. The downside of algorithmic reverb is that it can sound artificial, but that's okay, music production is not always about making things sound real or natural and algorithms can be used to create some really crazy reverb effects. 

Reverb Tricks and Tips

There is tons of information out there on how best to use reverb. This article from Sound on Sound is an excellent starting point, covering many of the fundamentals in impressive detail:

https://www.soundonsound.com/techniques/how-use-reverb-pro-1

However, the really interesting techniques are apparent when you scratch around the surface. Below you'll find a list of some of the coolest ways reverb is used or has been used to make tracks better.

The Bowie 'Heroes' Vocal 

Using three microphones positioned at ever increasing distances from David Bowie and two gates (see previous post for more on gates), Toni Visconti managed to harness the natural room reverb to create one of the most iconic vocal recordings ever. Watch him discuss it here:

The Abbey Road Reverb Trick 

This trick is all about how certain frequencies react better than others to reverb. Many of you will already be aware that reverb and extreme low and high frequencies often do not get on too well. This trick avoids that problem by inserting an EQ in front of the reverb in the signal chain. The EQ is then used (and this is where the 'magic' lies) to cut all frequencies below 600Hz and above 10kHz. This means that the reverb is only acting on a specific band of the vocals, proven over many a mixing session to give great, 'mud' free results! See a demonstration here: 

Reverse Reverb

Another quite simple trick with some great results, reverse reverb has been used many times over the years. The basic concept is the idea that you reverse a reverb 'tail' (the dying away of the sound) and use it to introduce a new sound or passage. This works best on sounds with fast attacks as the reverse reverb can help smooth or build the transition. 

To do this technique, we simply cut the first note from the audio and drop it on to a new track. 

Next we reverse the audio clip of the note and apply lots of reverb. Then we bounce the resulting file to create a longer version of the reversed note with a long reverb tail. 

Finally, reverse the new file and stitch it to the rest of the part (with a crossfade in this example), so that the original note plays correctly but the reverb tail now occurs before it plays. This makes the tail a great introduction for the new part or to help bridge the gap between sections of a piece. 

Listen here

Decay Time Calculations

In order to make your reverb effects more 'musical' you might like to adjust the decay time to sync with the tempo of a track. Logic Pro X has a neat feature to make this process quicker. Using the inspector, you can find out how many milliseconds a musical value (1/8, 1/16 etc.) lasts for at your current tempo. You can then set the decay time of your reverb to be in time with your peice. See demonstration here:

Reverb Freeze

This is a great technique for making expansive ambient soundscapes, interesting builds and sound effects, amongst other things... In fact it's just a great technique all round! It works by using a feature on some plugins* to 'freeze' the reverb tail at a certain point in time. Listen here

This technique becomes really exciting when you apply other effects after the frozen reverb. An effect with some movement might work well, like a modulation or filter effect. You could play with time-stretching the tail for a granular sound and, of course, you may even add some more reverb too. Demo here:

*Not all reverb plugins allow you to do this, but Chromaverb in Logic Pro X or Ableton's stock reverb effect have this feature. If you are on another DAW, Ambience is a free reverb plugin which includes freeze functionality. 

...and Finally, Eno/Lanois

I couldn't end a post on reverb without mentioning Brian Eno/ Daniel Lanois! Their famous modulating Shimmer reverb is one of the best. So here's an article on how to create it, written by the makers of a great range of reverb plugins (including Shimmer). 

And here it is in action! Enjoy.

More tips and tricks: 

Here are a selection of articles and videos highlighting even more reverb tricks and tips for you to try out.

https://www.izotope.com/en/learn/6-creative-reverb-techniques-in-music-production.html

https://www.waves.com/ways-to-enhance-reverb-and-delay-with-compression-and-eq

https://ask.audio/articles/5-reverb-techniques-that-wont-drown-your-mix

https://www.izotope.com/en/learn/reflecting-on-reverb-what-it-is-and-how-to-use-it.html

https://www.youtube.com/watch?v=XIkii9fF2Sg
https://www.uaudio.com/blog/reverb-roundtable/

Free Reverb Plugins!

Valhalla - https://valhalladsp.com/shop/reverb/valhalla-supermassive/

Tal-Reverb-4 - http://bit.ly/Tal-Reverb-4

OldSkoolVerb - http://bit.ly/OldSkoolVerb

MCharm Reverb - http://bit.ly/MCharmVerb

OrilRiver - http://bit.ly/KVR-OrilRiver

MVerb2020 - http://bit.ly/MVerb2020 

MuVerb - http://bit.ly/MuToolsMuLab

Dragonfly Reverb - http://bit.ly/DragonFly-Reverb

Riviera - http://bit.ly/Riviera-Reverb

Sanford Reverb - http://bit.ly/Sanford-Plugins

Reverb Solo - http://bit.ly/Reverb_Solo 

ProtoVerb - http://bit.ly/U-He_ProtoVerb

Convology XT - http://bit.ly/ConvologyXT

Safe Reverb - http://bit.ly/SafePlugins

Tila 2 - http://bit.ly/Tila-2

DD Reverb - http://bit.ly/DD_Software

Tal-Reverb-2 - http://bit.ly/Tal-Reverb-2

Ambience Reverb - http://bit.ly/AmbienceReverb

Ambient Reverb - http://bit.ly/KVR-Ambient-Reverb

Abstract Chamber - http://bit.ly/KVR-AbstractChamber

GigaVerb - http://bit.ly/V4F-GigaVerb

Next...

In the next bog post, we will continue to look at time-based effects. As always, please comment or email with questions or suggestions. Your feedback is really important. 

Take care, 
Ian

References

https://www.sweetwater.com/insync/early-reflections/
https://www.izotope.com/en/learn/reflecting-on-reverb-what-it-is-and-how-to-use-it.html
https://reverb.com/uk/news/6-echo-chambers-that-shaped-the-sound-of-popular-music?locale=en-GB
https://anasounds.com/analog-spring-reverb-how-it-works/