A multi-disciplinary designer’s journey in field recording, sound design, sound effects, and music.

Recording Single Waves

Posted: February 20th, 2012 | Author: | Filed under: field recording, nature recording, sound design

Look carefully: Deep impact zone, short period, wind parallel to the shoreline. Not a good day for recording single waves. So...what is?

It’s easy to get recordings of roaring surf – which can often just sound like constant white noise – but it can be tough to get relatively clean recordings of individual waves. I’ve found that picking a good day and place to record single wave hits are a combination of marine forecasts and location, and that the size of the waves really doesn’t matter.

The only online article I’ve seen that mentions both field recording and marine forecasting has been published by Tim Prebble. In that excellent article, he describes finding gentle-surf days to record his amazing Seal Vocals SFX library. Sometimes finding those small- to moderate-swell days are sometimes the best days to record single wave crashes…but that’s not the only factor.

Single-wave recording conditions are largely defined by a mix of swell, wind, and location.

Swell is due to the large movements of water over great difference; swell is not the same as waves, which are usually wind-driven. Swell is usually forecast based on buoys offshore, and is forecast days in advance. However, I find that 2-day swell forecasts are the most accurate. Swell is defined by wavelength and amplitude, just like audio: Wavelength is is measured in seconds (usually called period), and amplitude (usually called height) is based in feet or meters. Ideally, you want swell with long periods, because that means there’s a greater volume of water moving, but tall swell is also your friend, because that also influences breaking-wave heights at the shore. (Tip: Waves come in “sets” of big and small, between 3 and 8 waves each, depending on if there are multiple wavetrains that are in or out of sync. That means record for far longer than you’d otherwise think in order to get a good range of big vs. small waves over time.)

Getting back to the topic of wind, not all wind is bad (and we all know what wind does to field recordings: huge amounts of badness.) Offshore winds (those that come off of the shore – yes, that is totally confusing!) will might wave faces up longer than they’d be up otherwise, causing a moment of quiet before the wave breaks (or “closes out,” in surf parlance) and a potentially taller wave face. Wind coming onshore (onto the shore from the water) often smears the wave tops and can cause premature toppling…not to mention the fact that the wind will be blowing directly at your microphone capsules. (Tip: You can’t be at the shore without shorebirds, often noisy ones. Bird feeding activity, and therefore noise, may peak before an oncoming storm. Watch the forecast and choose clear weeks with low-pressure days, when it requires more energy to fly, when possible to reduce avian noise. Gulls are complete bastards in this regard!)

Finally, this brings us to location. Some of this is taste: Do you want to record breaking waves against sand, or against rock? Very different sounds will come out of each; bigger crashes will happen on rocks as opposed to sand. But beyond that, know a bit about your location. What direction is the swell and wind coming from, relative to where you’ll be facing? How does the land curve around, creating refraction waves? What is the slant of the land below the shoreline? This last one is especially critical, as the gentler the slope, the bigger the wave. The “impact zone” – where the waves actually break – can be deep or narrow, and a narrower impact zone will generate fewer audible breaking waves at once. Knowing if a beach has a “dumping break” is useful: It makes it terrible to launch from or surf near, but that also means the waves break right at the shoreline, which is far better for audio recording. Just watch out for your gear. (Not a tip, but trivia: Waves always break when the water depth is 1.3x to 1.5x the wave height, as the horizontal energy of the swell gets forced upwards to create breaking-wave heights near shore.)

Never turn your back to the sea. The sea is huge, powerful, indifferent, and above all, unpredictable. Rogue and “sneaker” waves are not legends or myths: They occur regularly, anywhere in the world. Don’t let a recording session end in tragedy.

A final note on technique: If you’re on a beach, angle the mic a bit more downwards than you’d think would be wise, and you’ll get nice sounds of the sand being pulled back as the breaking waves recede back into the ocean. Not always good to have in every recording, but this adds a lot more character. On a beach with fist-sized rocks, this can be especially cool!

I had a recent session at a sandy beach in the Point Reyes National Seashore that exemplified some of the better (but not quite perfect) conditions that I describe above. First, the wind was blowing at 20 knots…but from the opposite direction of the beach I was on, which was backed by hills. That meant delayed wave breaks and being protected from the wind. There was a southerly swell that came right into the dumping-break beach (I can tell the period is averaging 14 seconds by looking at the waveforms of the audio!), so it was all breaking swell and no wind-driven waves. It was a low-pressure day with a long-term clear forecast, and it wasn’t winter, when the masses of migratory birds come through Northern California. Only one swallow’s call made it into the recording.

The recordings aren’t all that dramatic when you consider the breaking waves were only 3-4′ high. But listening to this loud on headphones, eyes closed, I find that the sense of scale is quite exaggerated without an accompanying visual reference…a little Waves LoAir or layering some low-frequency booms can definitely can tip it into cinematically-big breaker territory if desired. However, even in a 90-second clip, there are only three really distinct wave “claps” as the bigger waves close out at the beach.

[Sennheiser MKH 30/50 mid-side stereo pair into Sound Devices 702 recorder]

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