Tetherd Cow Ahead

Computers have become so powerful now that it is possible to do things that are quite mind boggling. I have no doubt that you’re all aware of what’s going on in the realm of digital image, but us sound dudes can do some pretty cool stuff too.

Let me tell you about convolution reverb.

It is a truth universally acknowledged that no matter what your level of vocal talent, you will always sound better singing in the shower. The technical reason for this is that bathrooms have nice shiny reflective tile surfaces, and the reverberation off those surfaces allows you to hear your voice more clearly. ((It’s pretty hard to ‘hear’ your own voice in your head. When you sing, you are using reflections off the space in which you happen to be to judge your pitch – this is the reason that people often sing out of tune when they’re listening to music in headphones.))

It follows logically, then, that if you sound good in the shower, you’ll sound really good on stage at, say, the Sydney Opera House, with all its great reverberant reflections and acoustic properties. Of course, it’s not possible for you or me just to whip up an a capella version of Copacabana on the Sydney Opera House stage on a whim… or, at least it hasn’t been possible until now! Yes folks, not only can you now hear how your best Barry Manilow impersonation would sound onstage at the Sydney Opera House, but we can precisely simulate your performance in any acoustic space – caverns at Carlsbad… Wembley Stadium… Abbey Road studios… in a glass jar, a metal bucket or even a broom cupboard (where Barry Manilow would, arguably, sound most appropriate).

All this thanks to fast computer processing and ‘convolution’ mapping of acoustic spaces (stick with me folks, it’s pretty damn cool…)

As I’ve already mentioned, we gauge the details of the sound of a room by the reflections off surfaces in that room. Our ears are able to hear very small variations in frequency, and our brains, by comparing the information from one ear with the other, determine the exact aural characteristics of the environment we’re in. Quite obviously, every acoustic space is completely unique – it has an acoustic ‘fingerprint’ if you like – and we are able to very accurately judge aspects such as size, shape, harmonic frequencies and surface qualities of our surroundings. All this happens completely automatically of course – you don’t think ‘Ooh, I’m in a room thirty metres long with a fundamental harmonic frequency of 160Hz and plasterboard walls!’, but rather ‘This is a big hollow space!’ or ‘This is a cupboard!’

So, how does that become useful? When we record instruments of voices in a studio, we mostly strive to get the ‘cleanest’ most unaffected-by-the-environment recording we can, so that we may add acoustic effects such as reverberation and delay at some later date. This is done for two reasons – one is that any reverberant characteristics originally recorded with an instrument are ‘stuck’ to it – you cannot remove them. A flute recorded in a big church will always sound full and awash with reverb – nine times out of ten, that’s not desirable. The second reason that we prefer a ‘clean’ recording, is that we can apply reverb and other effects judiciously as we need, to make for a better and more pleasing balance in the audio mix.

When it comes to music recording and film sound, then, you can understand that being able to call up particular audio characteristics on demand has significant value. Up until now we’ve relied on artificially created approximations of real environments – good enough to fool your ear, but nothing like the real thing. Now, we can get so close to the real thing that even experts have trouble picking the difference. In other words, we can now use on our recordings the beautiful, real, rich ambiences that have been created in performance spaces and studios around the world. Or, if we need to, the sound spaces of interior cars, hallways, schoolrooms, water towers, aircraft hangars or jam jars – you can see how we film people might like that kind of thing.

So how is this impressive audio magic done? Well, if I don’t go into too much technical detail, it’s actually quite simple. We take a sound – optimally a tone sweep ((This is basically a sound that starts off really low in pitch and ‘sweeps’ to really high over a few seconds. A sharp transient sound like a pistol shot, or an electrical spark or a balloon pop can also be used – hence the term impulse response that you’ve heard me use.)) – and play it in the environment we want to model, re-recording it in high quality within the acoustics of that place. Then, using some fancy software, we compare that with a ‘pure’ version of the tone sweep. The software calculates the difference between the two sounds and uses that to build a map of the frequency responses and delays of the actual space. It takes my computer about a second to process the file – incredible. From this I get a ‘convolution map’ that I can then use in my audio software to apply to any other sound.

As I mentioned in my most recent post about Masthead Island, the Pisonia forest in the middle of the island had some very nice acoustic characteristics. I wasn’t able to take up equipment for making tone sweeps, but I recorded some ‘make-do’ resonses with sharp hand claps.

So, after such an exhausting technical lesson, I know you’ll want to hear some demonstrations of what I’ve been yammering about, and, lucky for you, I have prepared some earlier! So first of all, we need to start with our source sound, and I’m sure you’re way ahead of me with what that might be…

1. Here we have a duck’s quack as you might hear it in a field, with no acoustic reflections:

Download Raw Duck

2. Now, a duck as you might have heard it in the Pisonia forest on Masthead Island:

Download Forest Duck

3. Next, a duck on stage at the Sydney Opera House (as you might hear it from the stalls):

Download What’s Opera Duck?

4. And finally, a duck recorded in a washing machine just before you throw the spin cycle switch:

Download Washed Duck

There were, alas, no actual ducks on Masthead Island, but I can assure you, if there were, they would sound much like #2 above.

So, faifthful Acowlytes, that’s the TCA Crash Course in convolution spatial mapping. Your task for this week is to listen. That’s it: simply listen. As you walk about your daily lives, listen to the way your voice sounds in different rooms. Listen to the ambience on the street as sirens sweep by. Listen to yourself singing in the shower. Listen to how the sound of your voice changes as you walk from one room to another.

And marvel with me that we can now reproduce the acoustics of all those experiences exactly.

You know how good it sounded in the telling? It was better in the reality. If you can conjure up an image of a ‘Gothic Island Paradise’, Masthead Island is it. Probably just as well then that the film I’m working on is a ghost story…

My main regret is that I only had three days to spend on the island itself – the rest of the week was taken up with travel. It sure ain’t an easy place to get to. Or to escape from… (mwahahahaha!)

I can’t really talk too much about the film just yet – and anyway, no-one wants a creepy tale spoiled for them. Let me just say that the island itself is a significant character in the story and it fulfills its role better than I could have ever expected, with beautiful bone-white coral sand beaches, a lagoon the colour of nicely aged cyanide, and a dense interior of hollow Birdcatcher Pisonia glades edged with blurry casuarinas and Velvet Soldierbush, urgently whispering suggestions to visitors to leave before it’s too late…

I recorded the sound of waves on the distant reef, the shush of the casuarinas, the sombre lap of the incoming tide on broken coral. I made some wind chimes from shells and coral and recorded them in the quiet of the forest – a brittle, tinkling sound like dull glass merged with bamboo.

I also caught enough material to make the third CD in my Morphium series, Atoll.

I took some time to record some impulse responses inside the Pisonia forest – if that means nothing to you, stay tuned. Next post will be an explanation of a truly amazing invention of contemporary audio technology – a technique that allows us to make digital ‘maps’ of acoustic spaces.

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Special big thanks to Bronni for spotting & snapping this excellent signage!

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It has to be said that I have a pretty cool job. Over the years people have paid me to do all kinds of things that I would have happily done for free. Or even paid for myself. I’ve been paid to meet Spike Milligan. I’ve been paid to go to the top of the Sydney Harbour Bridge. I’ve been paid to have a 70 piece orchestra perform some of my music. I don’t tell you this by way of boasting – I say it only because I marvel at the wonderful experiences that life has brought my way.[tippy title=”*”]Lest you think it’s all been beer and skittles, I’ve also been paid to record to a knee operation, stand on a beach in New Zealand in sub zero temperatures for most of the night and visit the scene of a freshly-committed domestic murder – none of which I desire to do again.[/tippy]

Next week, some nice people are paying me to journey to Masthead Island, a completely pristine South Pacific island near the southern tip of the Great Barrier Reef. I am going there to record sound material for a new Australian feature film for which I’m composing music.

This is where Masthead is, in relationship to mainland Australia:

Masthead Island is a coral cay, and protected part of Capricornia Cays National Park. It takes two plane trips and two boat trips – the better part of a day’s travel – to get to there from where I live. There is no power on the island, no water and no shelter. The maximum number of people allowed on the island at any one time is 25. We will be about an hour’s fast boat ride from the nearest settled place.

This is my ‘lightweight’ recording kit. I’m taking my Zoom H4N digital recorder, and my sturdy RØDE NT4 (‘the rodent’) stereo microphone with its ‘fluffy dog’ windshield. There have been astonishing technical changes in my field since I started my career; the little Zoom recorder will allow me to record more than 6 hours of very high quality audio[tippy title=”†”]24bit/48k for all you tech heads – I can record at even higher and stupider levels of quality, but it would truly be a case of gilding the lily.[/tippy] on a 4g SD flash card. I’m taking 4 x 4g cards on this trip (and a big box of batteries, needless to say). 24+ continuous hours of recorded sound is more than enough for the 3 days I’ll be on the island.

When I first started in this business, the recording machine du jour was the Nagra 4 – a mono, reel-to-reel quarter inch tape recorder that cost a small fortune (I could never afford to own one) and weighed 6.4 kilograms (14lbs) with batteries. And that doesn’t include tapes, which typically allowed just 15 minutes of recording at the best possible quality. So, add another 4 kilos worth of tapes and mics and you can see that location recording was once a very weighty proposition. Lugging a Nagra around on a film shoot was almost guaranteed to give you back problems for weeks afterward.

My entire modern kit, including headphones, cables, microphone, windshield, recording media and enough batteries for a week, weighs less than half the weight of the Nagra recorder alone.

So. Off I go. It’s slightly daunting to be working somewhere so far from any modern facilities. There’s little tolerance for equipment malfunction so I’m relying on my tiny kit to hang in there. I’m nervous that I can’t back up any of my recordings immediately to disk as I do under normal circumstances. And I’m hoping that the production company, which is supplying our food, water and lodgings, hasn’t forgotten anything.

But I’ve met the rest of the crew and they seem like a decent bunch. And really, what could possibly go wrong?

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*Lest you think it’s all been beer and skittles, I’ve also been paid to record to a knee operation, stand on a beach in New Zealand in sub zero temperatures for most of the night and visit the scene of a freshly-committed domestic murder – none of which I desire to do again.

†24bit/48k for all you tech heads – I can record at even higher and stupider levels of quality, but it would truly be a case of gilding the lily.

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*Spawn Of Satan

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Matthew 19:24 – Again I tell you, it is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God.

Today’s assignment: Discuss the inherent paradox in this offer from Christian Debt Trust.