The Reverb Effect: What is it?

Effects: what’s out there and what do they actually do to sound? There’s a lot of ‘em, so if you’re already struggling to see the woods for the trees (or the other way around), then put the kettle on and make yourself comfy while we give you a glimpse of what’s possible. In this introductory blog, we’re poking our heads into the magical realm of reverb. Sprinkle it over your project to conjure atmosphere or completely submerge your track so it sounds like it’s calling to you from another world.

Reverb (Short for Reverberation)

Reverb is one of the most used effects of all time simply because it’s able to recreate a phenomenom that’s actually very natural. Whether you’re standing in your bedroom, in the attic, in a lift, concert hall or even on a peak in the Alps, everything you hear will be effected by the acoustics of where you are. This means that whenever you speak or pick up and play your instrument, the sound waves are thrown in every direction and bounce off any walls, windows or mountains that happen to be nearby, and ricochet back to your ears. The further away the wall or mountain is from the source of the sound, the longer it takes for the ricochets (or sound reflections) to make it back to your ears.

If you stand at the very centre of a gigantic cathedral, this can even take a good ten seconds! So, in practice, the reflections bouncing off the walls that are closer to the sound source return faster than the reflections bouncing off the walls that are further away. So you kind of get an uneven fan effect as multiple reflections return at different times. If you click your fingers in the middle of the cathedral, you’ll hear a distinct sound that gradually softens and gets quieter – that tails off. This ‘tail’ is actually what’s referred to as a reverb tail. A reverb tail has a kind of noisy and complex character but it’s precisely this effect that makes the church choir and the organ sound so overwhelmingly enormous.

Algorithmic

In the more virtual world of DSP (so, we’re talking chips and software), there are probably a billion ways to create a stunning reverb. The first is not only the most well-known but the cheapest – with an algorithm. The precise calculations made by this kind of reverb actually falls way outside the purview of this humble blog, but we will say that it creates a nice, juicy, and complex network of more simple echos. This is more than enough for a lot of producers and is actually able to shape some pretty gorgeous reverbs. For the sake of convenience, this algorithm-based reverb has also been made available in smaller formats like guitar and bass effect pedals.

Convolution

The second method is convolution. This stuff can be a little more tough to get your head around, but here’s the simplest explanation: Someone walks into a concert hall or church, fires a starting pistol, and uses a stereo microphone to record the reverb tail. What they’re doing is recording the ‘impulse response’. The starting pistol provides the impulse, and the reverb tail is the response. The reverb tail is like a fingerprint of the particular acoustics of a space, and using the right software, this fingerprint can actually be applied to the bit of guitar or vocals you just recorded! The advantage of convolution reverb might be obvious: since it’s able to mimic the acoustic qualities (or fingerprint) of a specific space, this can be authentically applied to any sound and without the need for any algorithms. Another advantage is that the system actually works in any space. So, if you want to shape your song with the acoustics of Abby Road Studios, or the Royal Albert Hall from the comfort of your back bedroom, then that’s actually possible! Want something bigger? How about Wembley Stadium or the O2 Arena? Someone only needs to load up their starting gun and lay the fingerprint down for you. Thankfully, a lot of companies have actually been busy doing this for quite some time and then offering the software you need to use them.

Click here to download some acoustic fingerprints from Sony! In the very least, these fingerprints are compatible with Acoustic Mirror (Sound Forge Pro – Windows)

There are, of course, some downsides to using convolution reverb. The technique can require some pretty hefty technology. In 1999, Sony introduced the DRE S777, a convolution reverb in a 2-unit, 19” rack with a price tag that totalled a good few thousand quid. Fortunately, you can spend much less on a computer and get pretty much the same result but this will demand a lot of heavy lifting from your processor. Another downside is that the characteristics of an acoustic fingerprint can’t really be adjusted, since this would mean shifting some walls that actually exist. Whoever wants ten unique acoustic fingerprints from the same space would need to make ten recordings of the impluse response. They’d set the stereo microphone up and leave it where it is, while firing their starting pistol from various points around the space.

Ok, so this isn’t actually entirely true. Of course the fingerprint can be adjusted, since it’s actually a set of data that’s being applied, not a concrete space. The data can also be simply loaded in as audio, and you’ll see a complex ‘piece of noise’ that diminishes in loudness towards the end. Any adjustments can actually be made as easily as applying an equaliser, compressor, stutter, or even another reverb. The question is, what kind of result do you get? Something like a marble statue standing in a concert hall will have an (albeit subtle) effect on the unique timbre of the reverb tail and is also represented in the acoustic fingerprint of the space. So, due to these kinds of specific details, the editing of a fingerprint can only be vague at best since it’s practically impossible to add an acoustic detail like a statue to a fingerprint with something as clumsy as a mouse or even a formula. So, by tweaking this kind of reverb, you not only lose some of the nuance of the space, but you can’t really add much to it either.

What you can do, which will no doubt appeal to the creatives, is just make your own fingerprint. And we don’t mean making a fingerprint of a hall or any other actual acoustic space, but from ‘something’. This can be a recording of an instrument, a snippet of film dialogue, or just a couple of counts of noise. Suppose you make a fingerprint of a harp-glissando and then apply the resulting reverb to every strike of a xylophone… you would then hear back the unique sound of a harp-glissando combined with the note of a xylophone. You might be shocked to learn that by using the ‘Acoustic Mirror’ effect from Sony Sound Forge, for example, it’s already been possible to create this effect for years!

Applying Reverb

So, now we have some sense of how reverb is ‘created’, we can dig into how reverb is actually used, which is much more fun. Reverb offers a number of benefits as well as consequences:

The first thing you imagine is a the kind of massive reverb you’d get in a big space. This is perfect for self-produced orchestral music, since in reality, orchestras actually play in pretty large spaces. Generally, reverb is used to add a sense of grandeur, even when, acoustically speaking, there’s no reason for it. Why’s that? Well, say you imagine that the music in your head is being played on a pristine, sandy beach. The beach itself is actually quite dry in terms of acoustics, so you’d actually hear very little natural reverb. But, since beaches tend to stretch far into the distance and you have the sea disappearing over the infinite looking horizon, adding some reverb to the music will give the suggestion of that immensity.

Why do (some) people sing in the shower? Simple: the walls of your bathroom kindly iron out any little intonation errors. How does it do this? You may have had the pleasure of hearing a school choir and noticed how they can sometimes sound like a litter of untrained cats. But if twenty or so ‘untrained cats’ are singing out of tune, all together at the same time, then a kind of average pitch is hit, making it sound kind of nice. Someone hitting the note too low is compensated for by someone hitting the note too high and this results in a clean but wide pitch. If a solo voice is treated with a massive reverb, the reverb tail can have the effect of making one voice sound like a choir since every reflection is a repeat of the source sound. If a note is hit too low and then immediately sung a little too high, the ‘average’ of the note caused by the reverb would actually hit around the right pitch – although sounding wide (and much like the acoustics of your bathroom). Since a choir can sound more rich than a solo vocalist, a solo vocalist with an added, fat reverb sounds more rich. Because of this, you could also assume that reverb added to a solo instrument will also make it sound more rich. In this case, it needs to be an instrument where the pitch can be subtly corrected while playing. Trying out this trick while playing an instrument like an accordian is simply not possible while something like a violin can definitely pull it off. Older analogue synthesizers are notorious for tuning instability, but the wavering pitch combined with reverb actually worked in its favour. This is actually a great tip if you want to start designing sound using a synthesizer – use something like vibrato, and if possible, an irregular vibrato to fluctuate the pitch then throw on some reverb to get fat and rich effect!

By using lashings of reverb, the sound gets diffused, more vague, ‘blurred’, and expansive. For specific genres, this effect is more than welcome, like Ambient, New Age, or Dream Pop. This kind of work is used a lot in television, gaming, and film soundtracks. But be wary of who you talk to about big reverb. If you’re talking to a mixing engineer about standard pop, or a live sound tech who needs to amplifiy and mix an ensemble or band, then they might not be the biggest fans of heaping on the reverb since this usually spells disaster – in other words, feedback. The ideal reverb time is proportional to the tempo of the music. For fast-moving music, it’s usually best not to use too much reverb and to limit the reverberation tail a little, while slower, more relaxed music can definitely benefit from a good coating of forceful reverb. But these are obviously all decisions you can make yourself, no matter what other people might say – even this blog.

The Pitfalls of Reverb

There are a number of reverb character traits that come with their own particular consequences. Put a foot wrong in these areas and you can seriously, and quite brutally, screw up your production. So, maybe you want to write these golden rules on your studio wall.

Reverb Length

If the reverb tail is very long, then the individual notes of a melody tend get a bit blurred and mashed together, so it’s especially important to make sure that the reverb isn’t too present in the mid to low range so that it doesn’t mess with the tightness of the bass notes. Bass can’t really handle any overlapping reverb from the last note played, so the overlap doesn’t really work that well. A way to counter this is to filter or equalise the reverb and shave off the mid to low end, or just cut it off, keeping your bassline tight and clean.

Up at the high end, you can be a little more liberal with your reverb. The higher pitched strings of a harp, piano, violin, or guitar, for example, get in the way of each other much less than the lower pitched strings.

Do you play live shows or love improvising? Then ‘anticipation’ is the magic word and you can probably play comfortably with a fat layer of reverb. The reverb will kind of let you know when things are starting to get messy and as a musician, you’ll pick this up pretty quickly. Before you know it, you’ll be playing in a way that will work whether the reverb is short or infinitely long. This principle is compatible to the sustain pedal of a piano. If you hold the pedal down while you play, you’ll quickly notice what works and what really doesn’t work and this effect translates into pretty much any use of reverb.

Reverb Width

Generally, a good reverb will have a nice stereo sound to it, or even surround sound. This ensures that if you’re using an acoustic fingerprint, the left audio reproduction will be different from the right, resulting in a lush and spacious sound. The downside of this is that if you put all of your instruments (to a lesser or larger degree) through the same reverb treatment, then everything has the same size and width. This might sound good on paper, but in terms of the overall audio image, a kind of saturation occurs very quickly, making your mix sound too diffused. A solution to this can be simply shrinking the reverb a little using a stereo-imager (software), or panning everything more to the middle of the effect-return of the mixing desk – of course this would only work if you’ve set up the reverb to return via two mono channels; each with their own panning. Orchestral music on the other hand, actually sounds great put through a wide reverb, so this rule is actually a little genre specific.

Reverb Brightness

With smaller or older sample-based synthesizers or keyboards, the samples (the pre-loaded sounds) can sound less lively than more modern samples. While the whole story gets a bit too tehcnical for this particular blog, the fact is that small, static samples can sound a little dead. Adding a little reverb to samples like this can inject a little life into them, as long as enough of the high-end is reflected and the reverb tail is nice and long. It’s a bit like ‘tishhhhhhhh’ (a lot of high-end) versus ‘tisuuuoooooooeeeewww’ (a decrease in the high-end). While enhancing the high-end and adding a long tail is a great solution, it can start to sound harsh. Using a super-bright sounding reverb in your mix can result in a big mess that starts sounding cheap. So tweak, listen, tweak again, and beware!

The other pitfall is that this kind of reverb can sound unrealistic. The natural acoustic reverb of a real space like a church or concert hall will eventually lose the high-end due to the materials of walls, curtains, any wood… or, in fact, anything that makes up the space. These materials absorb the energy of the sound, especially the higher frequencies – in fact – the high-end is the first to lose out, and sometimes, this can be a good thing. Anyone who wants to treat a mix to some artificial reverb shouldn’t be scared of the reverb sounding a little lifeless since too much life – or too much brightness, can actually sound even more artificial. In the case of convolution reverb, you’re unlikely to have this problem at all since the acoustic fingerprint is literally taken from reality – as in, life.

It’s a Bit Too Much

Say you want to add some expansive grandeur to the sound but a big, intense reverb is a bit too much. You could opt for a more subtle reverb and back it up with an even more subtle delay (maybe with a little feedback). Of course, the delay will also create more echo or reflections but they’re much less intense than the reverb reflections.

To Finish…

Reverb is a phenomenon that is better dealt with after you’ve stacked up some hours of experience working with it. In this sense, it’s like learning to drive: you can’t develop that extra-sensory gut ‘feeling’ for it in the space of a single day. With reverb, it’s definitely possible to pump some life into a piece of music, but it’s worth being careful how much ‘life’ you ‘pump’ in, since it might actually end up killing it off completely.