The View Up Here

Random scribblings about kites, photography, machining, and anything else

Archive for December, 2016

(Yet More) Microphone Tests

Posted by Tom Benedict on 19/12/2016

Since writing my last post Homero Leal pointed out that I could mitigate some of the harshness of the Alice microphone (for field recording, mind you) by adding a capacitor across the 2.2k drain resistor. I didn’t have the size I needed (6.8nF), but I had everything to make a similar modification by adding an 8.2nF capacitor in series with a 750 ohm resistor, both across the 2.2k drain resistor. All of this is spelled out in Ricardo Lee’s ChinaMod+U87.doc file on the micbuilder forum.

Alice with ChinaMod U87

I walked out into the park behind my work, recorded for about five minutes, and headed back inside to modify the microphone. After adding the HF EQ mod I walked back out into the park and recorded again.

Prior to the mod my recording had a background hiss that sounded like microphone self-noise. I knew from testing the mic inside my car that it’s not, and is actually a sound from the environment. While testing the mic with a 22″ parabolic dish a couple of weeks ago I panned around to try to identify the source. I’m almost certain the hiss comes from the sounds of tree leaves rattling against each other in the wind. It only takes a breath of wind to make the leaves rattle, so the sound is almost always there. After the mod, that background hiss was reduced quite a bit. Enough so that I wanted to try it more rigorously out in the field.

Last night conditions were almost perfect. We had a storm system rolling in, the air was still, and the sky was overcast. Perfect conditions for people to stay home, get off the road, and let people like me lurk in the shadows with headphones on. I packed both my Alice microphones along with my SASS and Olson Wing, and headed out to an old cane haul road to record coqui frogs and insects. I was rained out in the end, but even that worked to my favor.

The tests!

Alice with HF EQ vs. Stock Alice

This is an A-B test between the Alice with Ricardo Lee’s HF EQ mod (thanks for the pointer, Homero!) and an unmodified Alice. The mics alternate every ten seconds, with a two-second cross-fade. That’s probably excessive on the cross-fade, but c’est la vie. Keep in mind there was very little wind during the test, so the difference is subtle. But it’s there.

SASS vs Olson Wing

While I was there I also tested the SASS against the Olson Wing. In this case both were populated with Primo EM-172 capsules. After I got home I realized I had wind protection on the SASS, but none on the Olson Wing. So this isn’t a fair test of frequency response, but it should be a fair test of the depth of stereo imaging, and to some degree, sound localization. (The frogs really don’t move around that much.)

I was content to let this setup run for a while, but it started to rain. Without any rain protection on either array, I knew the rain would eventually soak the mics. So I packed it all in and pulled out my rain gear.

Rain Gear

I’m still trying to get a good, clean recording of rain. A while back I took a tip from Gordon Hempton and built a microphone rain shelter. It’s a hard aluminum plate covered with two inches of non-woven air filter material. The aluminum plate keeps the mics dry, and the filter material diffuses the rain drops to a soft “fuff” sound. I also added a layer of carpet foam underneath to cut down on the residual “fuff” sound. It’s set up to take my DIY shock isolator, a small ball head, and my ORTF bar. (Sorry, no pictures of the whole setup just yet.) With the whole mess set up on a tripod or c-stand, it protects the mics from rain while minimizing the sound of the drops hitting the rig.

Finally finally I had a chance to use it in the field. And it worked! It worked great!

Only problem is that I managed to damage one of my EM-184 cardioids while testing the Alice mics. It barely responded at all, and produced a deep wumping noise in the recording instead. So the stereo recording is rubbish, unfortunately. I thought the wump sound was the mic picking up rain drops hitting the tripod legs, so I switched to a c-stand, re-arranged, tied up cables, did all sorts of things. None of it helped. After about half an hour I finally admitted to myself that the mic wasn’t working, and packed it all in.

But the rain gear worked! It worked great!

And once I dried the EM-184 mics out they worked great again, too. (Lesson learned:Don’t let it rain on your mics. DOH!)

All in all it was a good night of testing. I have one other test I’d like to do with the two Alice mics (ocean waves!), and I’d like to do one more side-by-side of the SASS and the Olson Wing to see if I can shorten the length of the Olson Wing and still get a good boundary effect out of it. But I’m pleased as punch with the rain gear.

Tom

P.S. I also learned that I need to finish this project before watching another season of Stranger Things. There’s something about driving way the hell out on some abandoned road to some spot in the woods in the middle of nowhere with fog and rain and nothing but the buzz of the insects and the calls of the frogs to… WHAT THE HELL WAS THAT?!

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Whales, Waves, and Unexpected Urination

Posted by Tom Benedict on 12/12/2016

“See any whales?”

I’d been recording at Kiholo Bay for several hours before the man spoke to me, but the first hour had been plagued by technical issues. For some reason my DR-70D kept reporting a write timeout error – something usually attributed to using a slow memory card – but I knew the card was good. Helicopters and airplanes had ruined the rest of the first hour.

At that point I was almost done with my first completely clean hour of waves on my SASS and Mid-Side setup. My other recorder, a DR-05, was positioned at a small beach to the south of me, recording waves receding off of loose pebbles.

I turned around to see who’d spoken to me. He was an older man who’d been hiking along the coast and had stopped to talk. I knew his words would show up on the recording, so I figured if I’m editing I’m editing. I might as well be civil about it.

“No, not from here.”

He nodded and walked on. I turned back to my gear, but out of the corner of my eye I saw him turn and head down to the little pebble beach.

People here are, on the whole, really nice about other people’s stuff. At one point years ago I left some kites at Hapuna Beach, one of the busiest beaches on the Big Island. It wasn’t until I was unloading my car at home that I realized my kite bag was missing. I jumped back into my car, headed back to the beach, and found that someone had brought my kites up off of the sand and left them for me at the showers. People here really are great.

But still… Strange guy hiking down to a beach where I’d left gear… I didn’t want him knocking my gear over inadvertently or anything. So I kept an eye on him as he made his way down to the beach and… proceeded to relieve himself not four feet from where I’d left my gear. Recording sound. All sound. Beach sound. And now his sound. His very personal sound. He kept glancing up at me like I was being rude. I did turn away while he was occupied with his… task. But eventually I knew he’d finish and realize I’d been recording him. Which he eventually did.

One of my more awkward sessions.

(But I got a lot of really good winter wave on rock sounds!)

Anyway, I think I’ve finally answered some open-ended questions about microphones. The Alice microphones I’ve been building are beautiful, crisp, and punchy, but not all that great for recording outdoor sounds. They’re very bright, which works great for a number of subjects. Waves, streams, and wind in the trees just don’t happen to be any of those subjects. Unfortunately those are the subjects I’m interested in.

I also don’t think I’m a huge fan of mid-side recording for creating big spacious soundscapes. No matter how much I play with the balance of mid to side, I just can’t get as much of a sense of space as I do with the SASS. I find myself firmly in the camp of the partially baffled microphone array. So for now I’ll save the mid-side and LDC Alice mics for indoor recording and go back to my Primo-based mics for nature. (Though I still intend to convert my Behringer C-2 mics to surface-mount Alice electronics. They’ll make good instrument mics, if nothing else.)

There’s one last test I want to repeat, though. Early on I built an Olson Wing – a baffled double-boundary array invented by Curt Olson. This pre-dated my SASS. I remember I liked the sound, but that I liked the sound of my SASS better. Now that I’ve had a chance to try a number of other stereo recording techniques (X-Y, A-B, ORTF, M-S, and SASS), I’d like to resurrect my Olson Wing and try it and the SASS side-by-side. I’ve still got all the bits, so it’s just a matter of rigging everything back up and getting out with the gear.

It’s something of a pressing question because of something else that happened. Earlier today my wife bought me an early present: a pair of ammo boxes.

I joked with the kids that they’re for the Zombie Apocalypse. They just rolled their eyes. They know me too well. She got me the ammo boxes for a recording project.

One of the problems with unattended recording is that conditions change, weather turns, and gear gets rained on. My first unattended overnight session wound up that way. I set up to record the dawn chorus in the Upper Waiakea Forest Reserve on International Dawn Chorus Day, but during the night the clouds came in and rained on my gear. The evening chorus was spectacular, but with the rain on the leaf mast making a staccato drumming sound, the dawn chorus part of the recording was practically useless.

My gear survived, but the weather proofing was tentative at best. I’ve been looking for a good way to build a completely watertight, rain proof recording setup. Enter the ammo box.

Ammo boxes are made out of steel. They’re tough. And they have a rubber weather seal that’ll keep out a hurricane. Perfect for cramming recording gear into! My plan is to use the larger of the two boxes to house my gear, and either build an Olson Wing or an SASS around the box, depending on which one I like better. The microphones would be the only thing poking out. Everything else goes inside the box, which can then be latched shut. The whole unit can then be left overnight without any chance of rain getting inside and killing my gear.

Or pee, for that matter.

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