I swear I had another thread about this, but I can't find it for the life of me. So if this is repetitious, I apologize.
After watching Nicolas Chorier's video tests in Pondicherry, India, I dropped a number of KAP projects I was working on, including re-packaging my transmitter, and went off on the tangent of kite aerial sound. Going in, I thought this would be a straightforward project. Now that I'm months into it, I realize there's a lot more to it than I thought.
I'm less than a week away from what I hope will be the last end-to-end test of my gear. I'm putting this out here because it may be of interest to anyone doing video from a kite, or to create ambient recordings for use with still photography slide shows, which is more along the lines of what I'm planning. Before getting into what I've done so far, here's a quick intro to sound. Skip if it's boring:
With video, at least, sound is as important as the moving picture image. I'd argue that it's not as necessary with a slide show, but that it helps. One of the most common complaints about videos that I see on the RCGroups forum is the choice of music for the sound track. (I think this has to do with the tendency to pair RC airplane videos with "Highway to the Danger Zone" by Kenny Loggins or to "Rock You Like a Hurricane" by the Scorpions. No takers so far on the Pachelbel Canon.) Music tastes vary, but people seem to be drawn toward videos with good ambient sound tracks. At least there are fewer complaints about them.
Sound requires just as much care and thought about equipment and technique in the field as photography does. But just as our KAP equipment is always a compromise between quality, weight, and cost, so too is sound equipment. There's no one perfect answer, and everyone's answer will be slightly different.
Recording sound requires a couple of pieces of equipment: A recorder, a preamp (if the recorder doesn't have its own), a microphone, a cable, and wind protection since we're doing this outdoors.
Recorders need relatively low noise, a decent feature set, the ability to save high-quality file formats, and a good interface for the mic. Fortunately, a recent proliferation in handheld recorders makes picking up a KAP-weight recorder straightforward.
Microphones also need to have low self-noise, but beyond that they tend to be selected based on the application (shotgun for isolating a sound source, parabolic for picking up remote sound, dynamics for recording loud sounds, condensers for recording quiet sounds, etc.) Since the ambient soundscape is such a broad subject, omni-directional condensers work great. Most pocket sound recorders come with a pair built-in, though I went a different route with mine, as you'll see.
Cables need to have good shielding to cut EM/RF noise, high quality connectors, and decent mechanical strength. These can be bought commercially, though it's easy enough to build your own with good quality microphone cable.
And then there's wind protection. Almost any time you use a microphone outdoors, you need wind protection of some sort. Since I'm planning to hang all this stuff from a kite, it's an absolute must.
Now on to what I've done so far:
I want to record ambient sound from the air. More specifically, I want to record stereo ambient sound. The recorder I'm using is a Tascam DR-05. It's about as heavy as a compact camera and will record 24-bit 96KHz audio, which is overkill for what I'm trying to do. But it has its own preamps, has built-in omni condensers, and you can get wind protection for the DR-05 on Ebay for not much money.
I tried flying my DR-05 and using the built-in microphones, but everything sounded flat. There was no stereo separation, and I couldn't locate myself in space just by listening. There's an idiom in sound recording: If in doubt, get closer. (Hey! Sounds like photography!) This helps isolate a sound from the background, allows you to turn down the gain and get lower noise, and it creates a stronger stereo separation. Unfortunately since I'm trying to do all this from a kite several hundred feet away, none of that really applies. So I went off on another tangent and built a stereo ambient sampling system (Try saying that ten times fast!)
The SASS was designed by Michael Billingsley for Crown Audio. They're not made any more, they're heavy for KAP work, and the mics weren't really suited for outdoor ambient recording, anyway. Over the years people have built their own so they can use the microphones of their choice. So that's what I did. It's a close compromise between weight and performance. It's made almost entirely from 0.2" birch plywood, the same wood I used to build my KAP 4x5 camera, and is filled with relatively high density foam.
The microphones I chose are Primo BT-EM172 capsules. They're about $10 USD apiece, and are about the lowest noise microphone in that price range. By way of comparison, Telinga sells matched pairs of lavalier mics for about $350 USD. Take them apart, and they're just a wire going to a BT-EM172 capsule. Even the pros use them. They really are nice.
I learned the hard way that omnidirectional condenser capsules need to be mounted flush to the front of their enclosure. My first set were mounted recessed by 4-5mm, as shown in the photo above. During testing I heard some weird resonances that I fixed by switching to a flush mount enclosure.
The whole mess comes in considerably under the weight of my DSLR KAP rig, so I'm pretty confident it'll fly just fine from practically any of my KAP kites. The only step left is wind protection.
Two companies manufacture the bulk of the wind protection used by field recordists and film crews: Rycote and Rode. If you ask on the sound forums, most people urge you to buy a windjammer from one of them. Unfortunately neither Rycote nor Rode make windjammers for DIY microphone projects like my SASS, so I'm making my own.
Windjammers use acoustically transparent artificial fur to cut the wind. Something between a 1"-2" pile is ideal. The backing is also important: the more porous, the better. Rycote includes a disclaimer with all of their windjammers: because the backing is so acoustically transparent, it doesn't have a rock-solid grip on all the furry hairs. So they shed. I found a company selling 2" gray artificial fur with a tendency to shed, and ordered a yard in the hopes it's at least sort of acoustically transparent. It should be here tomorrow. Sewing the windjammer is the last step before I can mount this to a kite and get it in the air. (I get the feeling this thing is going to look like a big gray sleeping tomcat hanging from a kite line. And people stare when I fly a KAP rig!)
Initially I'm planning to mount this to a long pendulum suspension. I think the pulleys on a Picavet will transmit too much sound to the microphones to be useful without isolating the microphones from the rig. My first rig will be a set-and-forget with no way to aim the mics in the air. (It's basically the ballhead off my PAP pole stuck on the bottom of a pendulum suspension.) My plan is to fly it over one of the beaches I frequent to see if it can record wind-free sound in KAP-grade wind, and to see if the SASS can create a strong enough spatial image given the distances involved.
Sorry to end this with a cliff-hanger, but that's all I've got for now. I hope to have some sound files to share early next week. Meanwhile if anyone's interested in what the SASS does with stereo sound on the ground, here are two samples:
Three cars moving from left to right on a wet highway:https://soundcloud.com/tnbenedict/three-cars-left-to-right
Waves crashing on a rocky shoreline with a pebble beach off to the left:https://soundcloud.com/tnbenedict/kiholo-bay-south
These are both relatively close-miced, so they'll sound better with headphones than speakers. Because the kite aerial sound will have more distance between the subject and the mic, it should sound fine either way.