The View Up Here

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

Archive for June, 2015

First DIY Microphone

Posted by Tom Benedict on 28/06/2015

I really meant my first DIY microphone to be a stereo mic, but I managed to kill one of my BT-EM172 microphone capsules before I finished the thing. I placed an order for three more from Frogloggers and wrote to them to find out what I’d done wrong. Gene from Frogloggers wrote back to tell me that the EM172s aren’t ESD sensitive, and he really didn’t know why the mic died. Even better, he threw an extra one in my order to replace the dead one. That’s customer service!

I built out my remaining cables as two stereos and one mono. I de-soldered my one good mic and put it on the end of the mono cable. I took a tip from Jonathan Green’s page on how to package the microphone once I was done. I didn’t use 1/4″ headphone plugs for housings the way he did, though. I made my own.

Mono Mic Disassembled

The body of the mic is a 0.625″ diameter piece of 6061 aluminum (scrapbox!) that I covered with Cerakote. This is what I used in place of the 1/4″ headphone plug housing on Jonathan’s page. The screen is some fine mesh stainless. I punched out a 1/2″ round using my wife’s disc cutters. The BT-EM172 capsule and cable are shown next, followed by a 1/2″ round of 6mm craft foam. I assembled the stack pretty much in the order shown. I slit the craft foam, fitted it around the cable, shoved it in behind the microphone, and filled the rest of the cavity with hot glue. (For what it’s worth, my hot glue skills are nowhere near as good as Jonathan’s!) Since the hot glue isn’t in direct contact with the mic capsule, I should be able to cut it out if I need to remove the mic in the future. For now, though, it’s sealed.

Mono Mic Assembled

The assembled mic still worked! (YAAAY!) I’m sure the sound is colored somewhat by the housing, but to my untrained ear the differences are impossible to detect. The mic is much more durable in its housing, so I think it’s a fair trade-off.

Just to make life easy I made five sets of parts so I can house the other four mics when they come in. But I think I may make a metal endcap for the other four in place of the hot glue.

No samples to share just yet, but I’m planning to use this in the field sooner rather than later.

– Tom

Advertisements

Posted in Audio | Leave a Comment »

Building Microphones

Posted by Tom Benedict on 23/06/2015

The BT-EM-172 microphone capsules I ordered from Frogloggers showed up over the weekend. I wired them into a disused headphone extender cable just to try them out, but headphone cables aren’t shielded, so it picked up all sorts of EM/RF noise that showed up as an unpleasant buzzing in my test recording.

Today the Mogami W3031 microphone cable I’d ordered from Redco Audio also showed up, so I built a new cable. I used a 3.5mm gold plated audio plug from Radio Shack, 6′ of the Mogami cable, and soldered the mics directly onto the end.

Holy… Freakin… Cow…

I tested everything in a relatively noisy environment, both electromagnetically and acoustically. The shielded cable worked wonders on the EM/RF noise, basically dropping it below what I could hear. (Yeah… really quantitative…) The mics themselves performed marvelously. I haven’t tested them with any sort of rigor, but the mics may be lower noise than the ones built into my DR-05. All in all this is a huge move forward toward building a kite aerial sound rig.

In other audio news, early last week I built a micro version of the Crown SASS baffled microphone array. This is another baffle design that’s trying to do the same job the Olson Wing tries to do: create stronger stereo separation in a recording. Just like my rendition of a micro Olson Wing, my rendition of a micro SASS left a lot to be desired: the geometry was off, the materials weren’t ideal, and I generally didn’t understand what I was doing until I’d already done it. But it worked! When I popped it on my DR-05, I clearly got better stereo separation than when I ran without it.

I had an unfortunate opportunity to test it in the field. In the middle of last week one of my daughter’s parakeets flew out of the house. The kids were able to track him visually for about an hour, but by the time I got home they’d lost sight of him. I pulled out my DR-05, popped my micro-SASS on the front, and walked around the neighborhood trying to locate her bird.

After about ten minutes of realizing I could locate practically any sound I was hearing by rotating the recorder, I started hearing parakeets! Multiple parakeets! I panned across the sound, and realized it was coming from the creek behind our house. YAY! I walked back through the neighborhood, tracking the sound of three parakeets all apparently in the same location. Right when I walked up our driveway, they stopped calling.

That’s when I saw my wife walk out of the creek with her cell phone. She’d been trying to attract the bird by playing parakeet sounds on it. Three parakeets, to be precise. I’d been tracking her! So the micro SASS, flawed though it was, performed quite well. I’m planning on building a larger one I can fly from a kite to record ocean waves from above.

Tom

P.S. My daughter’s parakeet is still missing, unfortunately. We put up signs, and my daughter is spending her afternoons looking for him. But at this point I’m not holding out too much hope.

Posted in Audio | Leave a Comment »

Tascam DR-05 Micro-Wing

Posted by Tom Benedict on 17/06/2015

After sorting out the issues of protecting the microphones from wind and isolating them from rig and line noise, the biggest remaining technical problem with recording sound from a kite is distance: KAP (or KAS) rigs are rarely very close to their subjects. Trying to record stereo sound at those distances presents its own challenges.

Fortunately, field recordists have been working on this problem for decades. All manner of stereo microphone arrays have been invented over the years to address this. My own experimentation has only just begun, but I’m starting with a known design: the Olson Wing.

After ordering the bits for the EM-172 microphone array, it struck me how the arrangement of the built-in microphones on the Tascam DR-05 might lend itself to a simple experiment. I decided to build a micro Olson Wing around the DR-05 to see if I can get any immediate benefits in terms of spatial separation of the two channels. But first, a little background:

Curt Olson’s microphone array article describes the experiments he did that led him to his wing design. Vicki Powys’s articles describe her own microphone arrays, including her own take on Curt Olson’s wing design. They also have information on alternate construction materials. Curt Olson made all of his arrays out of wood, but Vicki Powys favors high density closed cell foam (pool floaties, yoga blocks, craft foam, etc.) Vicki found that the acoustic differences between foam and wood are small enough that it doesn’t have a huge effect. I’m sure someone more experienced with sound could tell the difference, but I know I won’t be able to. This is important because heavy wood construction isn’t ideal for kite payloads.

(As a quick aside, Zach Poff’s article on the EM-172 mics misses one minor, but important point: a wiring diagram. Vicki Powys’s first article describing her microphone arrays includes that diagram, along with information about ganging multiple microphones on a single channel in the same array.)

I had some 6mm craft foam left over from another project, so I grabbed a razor blade and a cutting mat and got busy. Here’s what I came up with:

Kite Aerial Sound Experiments #1 - Micro Wing

It’s far from ideal for several reasons: The microphone spacing in most binaural arrays are close to that of the human head: 5.5-6″. This is closer to 2″. The microphones in the Olson Wing should be arranged in a forward-pointing direction. These are angled out significantly. (Vicki Powys did some experiments on angled wing arrays that indicate I may not be that far off the mark, though the wings on my array aren’t actually angled; just the mics.) Strictly speaking, the Olson Wing uses the microphones as boundary microphones, and needs them to be in contact with the flat surfaces of the wing. The geometry of the DR-05 doesn’t really let me do that unless I cut pockets into the foam, shaped to the body of the DR-05.

At this point I’m not looking for perfect, though. I’m looking for an indicator that I’m on the right track. So I took it outside to the highway and set it up on a tripod to record car passes – a fair test of stereo separation. I recorded two takes – one with the wing and one without – and tacked them together:

 

Neither of these is processed, except to pull out the two 16-second clips, and to add fades at either end.

Conclusions:

  1. I’m terrible at working with craft foam. This is something I need to rectify if I’m going to continue to use it as a construction material.
  2. This thing flutters hopelessly in the wind. If I go with this kind of construction in the air, I’ll need to make it a good bit more rigid than it currently is. (Maybe wood really is a better material!)
  3. The wing does make a difference, but it’s slight. For now I’m chalking that up to the deficiencies I listed above. I’ll move forward with the full-sized version when the EM-172 mics show up.
  4. I’d rather fly a kite than stand by a highway.

As far as experiments go, I’ll call this a success. It gave me information I can use to plan my next move: building a micro SASS around the DR-05.

– Tom

Posted in Audio | Leave a Comment »

KAS – aka In Over My Head (again)

Posted by Tom Benedict on 15/06/2015

Some years ago I was hot on the idea of launching a high altitude balloon, festooned with cameras I’d used for doing kite aerial photography. I still have some of the bits and pieces from the balloon payload I never built, including a really neat little styrofoam cooler a co-worker was throwing out. In the process I watched a ton of videos from high altitude balloons (HABs), but none of them struck me like one I found from a launch in Florida. Unfortunately I haven’t been able to find this video again, or I’d share it here. What set it apart from the others was the lack of a music sound track. Instead, it used the audio from the camera. What I heard blew me away.

The balloon was launched from a city park. In the video you can hear all the normal sounds of a park: kids playing, dogs barking, the launch team talking amongst themselves. Just after launch you continue to hear these things, but gradually they die out, to be replaced by sounds of nearby traffic. Eventually the traffic dies out, leaving only a siren wailing in the distance. Finally the only sound left is that of an airplane flying well below the balloon, which at that point is over 50,000′ above the ground. After that, nothing.

I never did build a HAB of my own, but that video made me fall in love with the idea of recording sound from the air. I tried using the microphones on my KAP cameras, but the on-camera audio, even on a camera like a Canon T2i, is pretty poor. The microphones are tiny, the sound is hissy, there’ s no wind protection, and the T2i has automatic gain control you can’t turn off. (Later models like the T5i have this as a menu setting. Good move, Canon!) A few years later when I got into doing video on the ground with my T2i, I got a separate audio recorder for just this reason. It didn’t take long before I flew the recorder on a kite, but the sound still wasn’t great. No fault of the recorder, mind you. It worked perfectly. But I could hear the rig servos, the Picavet pulleys, line sing, and everything else going on on the KAP rig. I gave it up as a bad idea until I could think about it more.

So I thought about it. And I researched it. And I started learning the intricacies of field recording. I hit on Paul Virostek’s blog and bought a copy of his first book, “Field Recording: From Research to Wrap”. If you’re interested in sound and field recording, I highly recommend Paul’s book. He doesn’t start with the assumption that you have to own the latest, greatest, most expensive equipment. He starts with the assumption that you want to record sound. It’s a good place to start.

I haven’t had a lot of time to pursue my hobbies recently. I spent the last nine days painting and re-flooring my house, and in all that time I picked up a camera only once: to photograph the new floor. But Saturday morning I found myself in Kailua-Kona with time on my hands before my next appointment. “Aha!” I thought, “I’ll go record the surf at the Old Airport Park!” I grabbed my field recording gear and headed that way.

What followed was a comedy of errors worthy of a Marx Brothers movie. I set up to record surf, only to hear a persistent helicopter sound. I looked up to see a whole slew of skydivers with US Army canopies, and a Chinook flying overhead. The skydivers were landing in the park. One of the points Paul makes over and over in his book is that field recordists need to approach things in terms of serendipity rather than ruined opportunity. I couldn’t record the surf because of the helicopter, but I could record a helicopter!

I ran over to the landing area in time to catch it. But the mics on my little field recorder were overwhelmed. By the time I’d dumped the gain enough not to clip, the helicopter had landed and the event was over. I stuck around for takeoff, only to find I’d accidentally paused the recording until the helicopter was out of range.

So I went back to the surf, only to find the skydivers had jumped again, and the Chinook was coming back down. Back to the landing field!

This time I got a better recording of the helicopter, but the crowd noise was a little overwhelming and I still clipped. I got a good recording of the takeoff, though. Back to the surf!

I finally got a good surf sequence, but at the tail end a large set of waves came in and swamped my location. I grabbed my gear before it got splashed, only to have my windjammer fall off the end of my recorder and into the water. It looked like a little floating hairball. I fished it out, rinsed it off, and called it a day of lessons learned. Two days later it’s still damp. One more lesson learned: don’t let these things get wet!

I’m still a fair way from being ready to try kite aerial sound again, but I’m getting closer. I know what went wrong with my earlier sessions. I  know I want to wire in the audio channel on my video transmitter and set up my ground unit with a headphone jack. I also want to test all my gear in a studio box to see if I’m picking up RF hum from the transmitter. I now have real motivation to change from Picavet to pendulum suspension for the rig. I know I need line dampers to take out line sing, even though the KAP community moved away from them years ago. The list is long.

After that it’s a question of building a KAS rig that’ll give me the aerial sound I want. Right now I’m looking at building a variation of Curt Olson’s Olson Wing using EM-172 capsules, which I found from Zach Poff’s article. I’ve got other supplies from an earlier attempt to build windjammers for a borrowed pair of lavalier mics that should let me cut down the wind noise as well. I’m still not sure what I’ll use all this for, but it should be fun.

– Tom

 

 

 

Posted in Audio, Engineering, Kite, Kite Aerial Photography | 2 Comments »

Gone Missing

Posted by Tom Benedict on 05/06/2015

I’ve been missing for some time now. I haven’t written in months, and haven’t pursued the things I said I’d pursue in my previous posts. In some ways I’ve been in a cocoon. In other ways I’ve been a chicken running back and forth across a busy highway. Life’s just like that sometimes.

Back in October my father had some serious health issues. I wasn’t there, and my family agreed that I wouldn’t help anyone by being there. I knew they were right, but it hammered home how far away I am from my family. I love my father dearly. I can’t stand the thought of never seeing him again.

Shortly after that my cousin and I got in touch again. I found out she’d gone into professional photography, and was setting up her own studio space. We talked about photography, art, pursuing a personal vision, and all the other things connected with our mutual love of creating photographs. We both finished up by saying how fun it would be to grab our cameras and head out together. But she’s a quarter of the way around the world from me, in Texas.

While setting the summer schedule at work, two of my co-workers announced they were taking their families on trips across the American Southwest. This is one of my favorite places on the planet. When I was a kid my family went on numerous road trips across the Southwest. As an adult I went on another road trip with my father, visiting places we’d never been when I was younger. I’ve been trying to figure out how to take my own family there, but never solved the problem of how to get there without breaking the bank. My co-workers’ announcements just hammered home how much I miss it. The last time I was in the Southwest was fifteen years ago. I haven’t seen it since.

I was struggling with all these thoughts when I saw a posting for an electronic engineer at the Hobby Eberly Telescope at McDonald Observatory in West Texas.

I first saw McDonald Observatory when I visited as an undergraduate astronomy student back in 1990. This was before HET was built. It’s also where I first met my wife. I visited several times afterward, usually with other friends. She was working for an astronomer at the time, so her visits were more work-oriented and kept her up at night, so to speak. Later, one of my housemates took over as director of the Visitor’s Center, so we had even more reason to visit. McDonald Observatory figured large in my life for many years, though I never actually worked there. But for so many reasons it’s been near and dear to my heart all this time.

So yeah, I applied for the job.

Earlier this week I got a phone call, letting me know interviews would be scheduled the following week. I talked it over with my boss this morning, and he agreed it would be a really good career move. It was a tough conversation for me, and I’m guessing it was tough for him, too. But it meant the world to me to have his blessing to pursue this.

I don’t know how much I’ll be writing in the next two months. I truly don’t know what the future holds. I just hope it’s bright.

– Tom

Posted in Uncategorized | 2 Comments »