Adventures In Audio

Add reverb to your recordings using the natural echo chamber technique

by David Mellor
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Yes of course you can add reverb to any instrument or vocal with a reverb plug-in. But this isn't *real* reverb. It's a digital imitation. Wouldn't you rather have the real thing?

Back in the olden days of recording, that's the 1950s, 60s and early 70s, commercial studios would have a room that they called an 'echo chamber'.

Unless a studio had been purpose-built, which was rare and is even rarer now, then it would probably be a room that they couldn't think of any other use for.

Preferably it would have hard surfaces and an irregular shape. If it wasn't hard enough and irregular enough, then you could throw in a couple of large-diameter concrete pipes to bounce sound around a bit more.

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In that room would be a loudspeaker and one or two microphones. Two mics are necessary for stereo. The loudspeaker - you only need one - should point away from the mics.

An engineer who wanted reverb on an instrument or vocal could send signal to the loudspeaker. Sound would bounce around the room creating reverberation which would be picked up by the mics. The engineer could then add the reverb to the mix.

Of course this isn't as quick, easy or convenient as a plug-in, but it works, it works well and, most importantly, creates a real sound texture that is difficult for a plug-in to imitate.

And...

The sound texture of reverb created in this way is unique. No other studio has the same room and therefore no other studio has the same reverb.

Echo chamber

The room used to create reverberation would commonly be called the 'echo chamber'. I don't know why it isn't the 'reverb chamber' but that's just the way things are due to history. Someone once called it an echo chamber and the terminology stuck.

Natural echo chamber

I like to generalise this terminology from the room itself to the technique, and so I call this technique the 'natural echo chamber', firstly to include the traditional terminology of the past and secondly to emphasise that this is natural, not electro-mechanical (that's another story) or digital.

Digital, in my book, is not natural. It's a convenience.

DIY echo chamber

So you have a home recording studio, and presumably a home. A spare amplifier, loudspeaker and couple of microphones? Then you have all the requirements to set up a do-it-yourself natural echo chamber. Oh, you may need some long cables to hook it all up.

Do this...

Take a spare output (meaning an output other than your main monitor outputs) from your audio interface (*see note at end). Route that to a power amplifier (or direct to your speaker if it's active). Route the amplifier to your speaker, placed in the room you have chosen to be your echo chamber. A stairwell often works nicely, if you have one.

Place microphones in your chamber so that they are not pointing at the speaker and for preference are not pointing head-on at a flat surface. As a nicety, you might consider placing the microphones so that they are each the same distance from their nearest hard surface. Other than that there isn't any 'right' positioning - It's all down to experimentation and finding what you like.

Abbey Road echo chamber

(The image above is of the echo chamber at Abbey Road Studios, from Google Presents: Inside Abbey Road)

Then go for it - Take a vocal (always good for a test) and set up an auxiliary send to send it to the chamber. Route the mics back to your mix and revel in the luxurious reverberation provided by your very own natural echo chamber. Then start tweaking everything so that you can explore the possibilities.

What does it sound like?

Interesting. It *will* sound interesting. Sometimes a natural echo chamber can sound actually natural. I heard a story once of a major classical music record label taking a rather dry recording to St. Giles Cripplegate, which is a noted orchestral recording venue, to add natural reverberation using exactly this method. That was told to me by a representative of the church when I was recording there myself.

St Giles, Cripplegate, London

But often the sound is, well, I'd say characterful rather than natural. Try this in a parking garage and you'll see what I mean.

So what does it really sound like?

I know. You want to hear it.

Well fortunately I have several examples recorded by Audio Masterclass students.

Snare drum

Firstly we have a dry recording of snare drum...

Here the snare is well-recorded and perfectly dry. The echo chamber is a 100 square metre empty shed. Bear in mind that it isn't the snare that's in the shed, it's the loudspeaker and microphones. Here's the sound from the shed...

100 square meters would be 10 metres by 10 metres, or equivalent, so it's bigger than the average garden shed. Considering that it's likely that the reflecting surfaces are wood then that would have an absorbing effect on the high frequencies in comparison to what we would hear from concrete.

Mixed together, the result sounds like this...

The mix is well-judged and subtle. It's important not to overdo things here, unless a very reverberant sound is required for an effect.

Speech

Let's move on to speech. Speech is usually very revealing of subtleties and imperfections in audio because we hear natural speech every day.

This seems to be a public information recording and is adequately clean and dry. Although it doesn't need any reverb to suit its purpose, it works well as demonstration material. Here's the reverb signal only...

The chamber is a tiled bathroom recorded through a Sterling Audio ST69 vacuum tube microphone.

Sterling Audio ST69
Did you notice something?

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The reverb is mono. Sometimes mono reverb can be a useful effect because it binds the reverb to the vocal or instrument rather than letting it wash around the stereo image. The mix sounds like this...

There is a higher level of reverb here than would normally be useful, but the requirement of the original task was to make a good demonstration, so that's fine. To my ears, it actually sounds like it was recorded in a bathroom. It's important in audio for film and TV to be able to synthesise acoustic environments convincingly, and this example does just that.

Guitar

My final example is of some excellent guitar playing. Here's the dry recording...

There does seem to be a tiny amount of reverb already. Normally when you use the natural echo chamber technique, you want the dry signal to be completely dry. But sometimes, as you will hear, it doesn't matter. Here's the reverb...

All I know is that the mics are a pair of Rode M3's. The M3 is probably what you'd call a budget mic at around $130, but it sounds excellent here.

The mix sounds like this...

Again the reverb is mixed in at quite a high level, but to my mind this really works well. It suits the sound of the dry guitar, the style of music, and the performance. First class.

Summary

So there we have it, the natural echo chamber is a great technique to try out and use on your own recordings. And when you've found exactly the sound you like, no-one else has it, or can have it. It's unique to you.

Credits

Snare drum: Andy Binder
Speech: Peter Drake
Guitar: Gideon Kantazih
Abbey Road Studios
St. Giles, Cripplegate: John Salmon CC BY-SA 2.0
Sterling Audio SA69
Rode M3

*This applies if you have outputs in addition to the main left and right monitor outputs. You can still use this technique even if you only have two outputs. The process is too long to cover here, but figuring it out by yourself will be a useful brain-expanding exercise for you to try.

Monday October 5, 2020

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David Mellor

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

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