SD101: Backwards Reverb

We’ve all heard the effect – they used it lots in the movie Poltergeists and also in a great Simpsons episode involving Homer in a 3D space he found behind a bookcase. I call it Backwards Reverb and have occasionally used the technique since back in the day when I was working with analogue multitrack tape. It was a bit trickier then, since when you reverse the roll of say 24 multitrack tape, you had to remember that what was on track 2 was now on track 23….. if your maths was a bit screwy then you risked erasing something crucial!
So, what I’m talking about is creating an effect where the reverb (or delays) precede the sound ie ramps up to the sound. This is different to the plugins that do reverse reverbs – this is a non-realtime process….. We obviously aren’t aiming for realism here, unless there is some technique to make time run backwards that I dont know about… but I think why the technique is very useful when applied in an appropriate context, is because it essentially generates interesting tonal sounds that are directly related to the sound they precede. In case you still dont get it, heres what I mean, take this piece of dialogue for example:
[audio:http://www.substation.co.nz/zstashedbits/bkwdsverb01.mp3]

Its relatively easy to do, the only tricky part (especially if you are applying it to dialogue) is the resyncing part… so heres a step by step method:

1. Take that bit of dialogue from the previous example, heres what it normally looks like:

2. Ok so drag a copy of it onto track 2, immediately below and then reverse it:

3. Now insert a reverb on track 2 (i’m using a TLSpace mono-stereo reverb),
We want to record the reverb onto another track so change the output of track 2
to stereo bus 1 and add a new stereo track 3 – set its input to stereo bus 1
Now record the reverb of the backwards dialogue onto track 3, like so:

4. Now drag a copy of that reverb onto a new stereo track 4 and reverse it, like so:

5. Now that we have the bits we need, we need to resync our backwards reverb on track 4 to the original file on track 1… so ignore track 2 and 3 for now (mute/hide them)
We need the end of the two regions to line up, as below:

Do this by either doing it roughly & then zooming in on the end of the region & tightening its position… or if you are in ProTools, you can use some sneaky command keys to do it perfectly: Put the cursor on track 1 and hit TAB until the cursor is at the end of the region… Hold CONTROL down and use the GRABBER tool to move the region on track 2 instantly in sync to the cursor position. Now hold down COMMAND and CONTROL and use the GRABBER tool again to automatically move the region backwards by its own length. Hey presto its perfectly aligned with the end.

This all might seem a little confusing – and if someone bugs me, I’ll try & use a screen capture program to do it in realtime & upload it on youtube but it takes some explaining so thought I’d try this way first. Do you understand? The same process works well using a delay instead of a reverb, so you can get delays ramping up to a sound….

The idea of recording reverbs is a handy one, for a number of reasons, the first of which is it frees up that reverb and/or CPU for other uses… Also if you were taking your session to another facility to mix it also means you dont have to worry about them having the same plugins. But the main aspect I really like of recording reverbs (whether they are forwards or backwards) is you are then able to edit and/or process them further, as we have here but also in other ways… A beautiful room reverb (eg a hall) sounds even more beautiful slowed/pitched down a bit!

As an example of using Backwards Reverb in sound design, I used it for the very first moments in the movie Perfect Strangers – the first frame of the film shows an extreme close up of someone cutting onions. When I started working on the film I realised that when its seen in a theatre that onion would be HUGE so I started experimenting with accentuating the sound of the knife cutting into the onion and the pieces of onion almost dancing as they came off the knife. I recorded a lot of very close up onion cutting sounds, at various speeds & got the sequence working kind of as I imagined… After I played it to the director, she liked it so much she decided to extend it prior to the film starting, starting off very slow & almost abstract & then becoming more real until it reveals onscreen… So I pitched down some of my onion cutting sounds and recorded more, slower ones but I needed a means of pushing them away from reality a bit – ahar! Time to try a backwards reverb on it. So I reversed a number of the sounds – the cutting sound and especially the wooden clunk as the knife hit the cutting board – applied various length reverbs, then reversed those reverbs & resynced them with the other ‘real’ effects… magic! It took some manipulating to make the elements all feel a part of the same moment, but it worked a treat and i remember playing the sequence to the composers on the film and they couldnt work out how I had done it…. when we mixed it we also had some fun by placing the start of the onion cut in the surrounds, so the slice basically passed through the audience, until it impacted at the front…. have a listen, its not quite as coherent without the images but you can get a feel for merging backwards reverbs with real effects…. You’ll notice we start introducing elements of the ambience during the transition from surreal to real, by the third chop you can hear the fridge and then you start to hear the kitchen etc…. bear in mind this is a stereo crash down of the 5.1 FX stem… crunched to mp3….
[audio:http://www.substation.co.nz/zstashedbits/PSonions.mp3]

3 Responses to SD101: Backwards Reverb

  1. Carl says:

    I do it slightly different to avoid the re-syncing bit. If you select a long bit of blank before doing the reversing (which adds a long bit of blank after reversing, with the audio moved earlier), and then do the reverb to this whole region, once you reverse it again, it’s automatically in sync. Hope that makes sense. Yes it is hard to describe this stuff using only prose.

  2. Pingback: Disquiet » Backwards Reverb Sound Design MP3s from Tim Prebble

  3. Pingback: Designing Sound » More than 50 Articles/Tutorials about Sound Design, Film and Recording, Plus Wooshes Sound Desing

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