The View Up Here

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

LDC Alice – Take Two

Posted by Tom Benedict on 16/09/2017

I decided to build another set of Alice microphones along the lines of Jules Ryckebusch’s Instructable, using the circuit originated by Scott Helmke, modified by Jules, and put in PCB form by Homero Leal. For these, though, I made a couple of changes:

When I built my first Alice microphone, I’d intended to use it for field recording. Unfortunately I found that the very qualities that give a vocal mic a lot of clarity and presence wind up making it extremely sensitive to the sound of wind in the treetops. It did a beautiful job, but was overly sensitive to wind hiss.

Homero came to my rescue and told me about a document written by another member of the Yahoo! micbuilder forum, Ricardo Lee, describing a modification I could make to the Alice circuit to tame the microphone’s presence peak. I rolled this change on my first Alice and on the Mid-Side Alice I built shortly after. The modification worked, and tamed the microphone’s over-sensitivity to wind hiss. I eventually put the modification on a switch so I could choose how the mic was voiced.

For this set of Alice mics I put those components on the PCB with a dedicated set of pads to wire in the switch, visible just to the left of the filter cap on the back of the board.

New PCBs

The next change I made was to use the Transound TSB-25AX capsule rather than the TSB-2555B capsule I’d used in my first Alice. From the datasheets on the Transound web page the two should behave almost identically, with the S/N performance of the 25AX just barely edging out that of the 2555B. To my ear the two sound identical.

Probably the biggest change was how I mounted the capsules. When I built my first Alice I didn’t own a 3D printer and still thought entirely in terms of subtractive machining (taking a chunk of stuff and cutting away whatever doesn’t look like what you want). This time I started over and designed a completely new saddle and post with 3D printing in mind. I wanted at least rudimentary shock mounting and a cleaner run for the wires.

Shock-Isolated Capsule Mount

I tried a number of approaches on shock mounting, but most of them strayed from something else I wanted out of this design: I wanted it to be something anyone could print and use. So I stuck with easily accessible materials for the shock mount itself, in the form of anti-vibration servo grommets available at practically any hobby shop.

Shock-Isolated Capsule Mount with Grommets

Shock-Isolated Capsule Mount Grommets Installed

As with all of the capsule saddles I’ve designed thus far, the capsule is attached using E6000 adhesive. This stuff is at least somewhat compliant, extremely sticky, and can be removed after the fact by passing a fine wire between the capsule and saddle. So far I haven’t needed to remove one, though.

I printed the final parts using Proto-Pasta Carbon Fiber PLA filament. It’s not the cheapest filament out there so I try to save it for lightweight structural parts, but it just looks so danged good, I couldn’t resist.

TSB-25AX Installed Front Quarter View

One of the things I like about 3D printing is that you can add features that are difficult to get any other way, except possibly by casting. In the case of this saddle and post, a 3mm tunnel runs from the back facet of the post down the center to take the capsule wires to the PCB inside the mic body. The tunnel has a 6mm radius curve inside the post, which makes wire installation easier.

TSB-25AX Installed Rear Quarter View

The final change I made was to switch from the admittedly gaudy BM-800 mic bodies I’d used on the previous two microphones to a slightly less gaudy un-branded BM-700 body I picked up off of Ebay for under $20USD. This had the added benefit of switching to a different headbasket geometry that doesn’t contribute as much ringing to the handling noise.

Here are all the bits and pieces going together. (I haven’t installed the voicing switch on this mic yet.)

Microphone Innards Front

Microphone Innards Rear

And a closer look at the wire routing, which is a lot more satisfying than the routing on my previous mics:

Headbasket Innards Rear

Here’s what it looks like closed up and ready to roll:

Microphone Front

For anyone else building their own condenser microphones, I’ve made this and a saddle for the TSB-2555B capsule available on Shapeways and Thingiverse. Be sure to print the right one for the capsule you’re using:

TSB-25AXZ3 Shapeways

TSB-25AXZ3 Thingiverse

TSB-2555BXZ3 Shapeways

TSB-2555BZ3 Thingiverse


Happy recording!



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Vacuum Chamber Camera Mounts

Posted by Tom Benedict on 26/07/2017

August 1st we’re taking our telescope apart so we can re-coat the mirror. To date I’ve helped coat mirrors from four telescopes on the mountain including those from CFHT (M1 and M2), Gemini North (M2), IRTF (M1), and UKIRT (M1). Later this year we’re coating the 2m M1 from the Las Cumbres Observatory Global Telescope Network’s Faulkes telescope on Maui. Next year (we think) we’ll add a fifth Big Island telescope to the list when we coat the M1, and two M2 mirrors from the University of Hawaii 88″.

All of these are done in the basement of the CFHT Observatory, my home away from home.

CFHT Aluminizing Room

Mirror coatings offer a unique opportunity to photograph a really cool process: going from a bare piece of glass to a mirror in under 60 seconds. The only problem? The coating chamber itself is one huge, opaque piece of steel.

The Chamber

Luckily, the chamber has two windows installed in it. One lets you view the mirror. The other lets you view the filaments that evaporate the aluminum onto the glass. They’re relatively small, with a clear aperture of seven inches, but with some careful arrangement it’s possible to position cameras to peer through them and photograph the flash.

But it’s not easy. In years past I’ve balanced tripods on relatively small platforms, bolted makeshift 80/20 frames above and below the windows to try to support cameras, and even resorted to using tape. At times my solutions have been downright ugly, but they’ve worked well enough to let me photograph the transition from glass to mirror.

Before and After - Telescope Mirror

This year I wised up. I asked my boss if I could spend a little money and solve this problem once and for all. “Sure,” was his reply. That one word solved everything.

The windows are held in place by a ten inch diameter ring and six 3/8″ bolts. I couldn’t modify the rings, but I could install longer bolts and add tabs that let me attach additional hardware.

With the tabs in place I was able to install four 11″ articulated arms that I ordered from Amazon (two per window). If I had the option I’d install more, but even with two the windows become crowded quickly.

Because the two windows offer such different views of the chamber, the photographic requirements differ as well:

The window on the top of the chamber – the one that offers the view of the filaments – is used for diagnostics: Did all of the filaments fire? Did the aluminum wick onto the filaments without dropping? Did the aluminum vaporize without spatter? These require a relatively wide angle view, so I mounted a GoPro on one of the arms. On the other I mounted a Pulnix low-light video camera that’s wired into a monitor down at the controls to the coating chamber.

Cameras on the top porthole

Because outside light will reflect off the chamber window, causing glare, when we’re using the cameras we have to keep them covered.

Top porthole black-bagged

The window on the side of the chamber – the one that offers a view of the mirror being coated – is used to observe the coating process. Was there arcing during the glow discharge stage? Did the glow discharge generate a usable plasma? Did all of the filaments fire? Did the glass get a coating of aluminum?

This window is a little more complicated. To observe the glow discharge and the filaments, we installed a convex mirror at the base of the window. A Gopro aimed at this mirror can see, albeit in a very distorted way, most of the filaments and almost all of the glow discharge cathode. To observe the mirror, I used a DSLR with an 11mm lens pressed flat against the window.

Cameras on the side porthole

The side window also needs to be protected from stray room light, and will be black-bagged the same way the upper window was. Before the next coating I’d like to make proper blackout bags to cover the windows, but for now the cloth-and-bungee method will work fine.

This year I hope we get some really excellent video and stills of our mirror coating without having to resort to duct tape and bailing wire!

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Camouflage, Paint, and Hiding in Plain Sight

Posted by Tom Benedict on 12/06/2017

I’m planning on using my weatherproof recording box to record wind in the rocks and grass at a remote lake up on a mountain, weather permitting. (Weather not permitting, I’ll record something else!) But the place I’m planning to record is primarily browns and reds rather than the greens I used to camouflage my weatherproof gear. It’s too late to change my gear now, but in the future I’ll need to think more about the camouflage I use to hide my stuff in plain sight.

Meanwhile an interesting discussion about camouflage took place on one of the field recording discussion groups on Facebook. In the discussion, someone raised the point that paints, fabrics, etc. that look fine to us in the spectrum we can see may be overly visible or downright jarring in the spectrum visible to some wildlife. The discussion centered around deer, which can see into the UV, but also applies to birds, insects, etc.

Since I’m already in the business of characterizing the reflected spectra of materials, surface treatments, paints, etc. I scanned the paints under discussion to see what their reflected spectra look like. I prepped the samples the same way I did for the SPIE paper: four coats, applied at roughly a 45 degree angle, coming in from the four cardinal directions.

Krylon Paint Reflectivity 250nm - 750nm

All of these are from the Krylon Ultra Flat Camo Paint series, one of which, their flat black, was part of the sample set I scanned for the paper I presented at the 2016 SPIE Astronomical Telescopes and Instrumentation conference in Edinburgh.

From 250nm to 750nm things look relatively normal. The behavior short of 350nm is more a function of the binders than the pigments, and all are relatively similar to the flat black, some even performing a little better in the near-UV.

From 350nm out to 650nm you see the action of the pigments in each of the paints. Khaki is fairly broad-spectrum, reflecting a good amount of reds, greens and blues, tending toward the redder end of the spectrum. The brown (which is quite dark) peaks in the red, with lower reflectivity in the greens and blues. The olive and light green peak at shorter wavelengths, favoring more greens than reds. It all makes sense until you look at the near-infrared.

Krylon Paint Reflectivity 250nm - 2500nm

That’s where it gets really weird. The Krylon flat black paints use carbon as a pigment, so they tend to stay low well into the NIR. The long tails on the brown, olive, and khaki paints aren’t surprising, especially given what I saw with some of the other samples I measured for the SPIE paper.

What’s weird is the light green paint. It’s more reflective in the NIR than any of the other pigments in the visible. I have no idea what they use for a pigment, but it’s got one heckuva NIR signature.

None of which may matter much when it comes to camouflage. Photosynthesizing vegetation is quite reflective in the NIR, so having one out of five colors reflect strongly at NIR wavelengths may actually help the disguised object blend better in plant settings.

In reading further about deer and their ability to see into the near-UV, I learned that there are two things at work: First, deer really can see further into the UV than we can. In the case of reindeer it helps them find the lichens that are one of their primary food sources and it helps deer spot UV-absorbing urine markers from predators.

The other factor at work is that the sensitivity of the blue receptors in deer eyes peak around 400nm, right around the center wavelength at which fabric and paper brighteners fluoresce when exposed to UV light. It’s this effect that makes white cotton shirts, shoestrings, and paper glow under black light.

The Shimadzu spectrophotometer I use to measure samples registers light of any wavelength, so it’s sensitive to fluorescence as well as directly reflected light. But just to be on the safe side I photographed the paint samples under UV illumination, as well as with an IR-converted camera, the same one I used for the SPIE paper.

Paint Three Ways

All in all, I think the Krylon Ultra Flat Camo paints are good to use as camouflage, both for humans and for wildlife. But I need to come up with a better color combination for blending with lava rock than the green scheme I’ve currently got on my gear.

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Weatherproof Recording Box – Part 2

Posted by Tom Benedict on 02/06/2017

A little while back I wrote about a weatherproof recording box I’d built so that I could do drop-and-recover field recording without having to care quite so much about the weather. The design had a couple of shortcomings, most of which I’ve been able to address. Since then I had the chance to take the revised box out into the field and put it through its paces. I’m happy with how it performed.

The two biggest issues I had with the first revision of the box were the heating problem I mentioned at the tail end of that article and the fact that with the connectors I was using, I couldn’t actually plug all four channels into my recorder and still have it fit in the box. I had a couple of minor issues as well, including the fact that the lid on the weatherproof outlet cover rattles. Here are all the changes I made to address these problems:

I fixed the rattle in the outlet cover with small snippets of weatherstripping. Nothing fancy, just adding enough spring to take out any tendency to rattle in the wind.

I also added strips of industrial strength Velcro to either side of the box. This makes it easy to use the box as a baffle and mount omnis on either side like tree ears. I’m not entirely happy with how this sounds, though, since the box represents a much harder boundary than tree bark does.

The way I solved the connector issue was to swap out all the Neutrik XLR plugs for low profile connectors from Cable Techniques. Redco Audio sells these for about $15US. They come with black caps, but Cable Techniques makes color caps for the connectors as well, so I was able to maintain the color coordination between the outside panel and the inside connectors.

Low Profile Plugs

While I was at it I bought a right-angle USB cable for the battery pack. In 20/20 hindsight I wish I’d bought one with a right angle connector at both ends instead of just at the micro-USB end. But at this point it’s just a nit-pick. The cable I got works fine.

Right Angle USB

With those two changes, everything now fits in the box with all the foam panels installed.

Everything Fits

Which brings me to the second major modification: In an edit to the last article I said that I’d tested everything with a temperature logger, and in a 21C room the air temperature inside the box had risen to 34C after eight hours of operation. What I didn’t take into account is that the battery and recorder were considerably warmer than the air in the box. The operating range on my DR-70D is 0C-40C. I wasn’t comfortable running it that close to the limit.

Thermal Pad
The foam panels in the box are all removable. They just wedge into place. So I pulled the two side panels and installed thermal pads. Thermal pads are made out of silicone that’s had thermally conductive additives mixed in. They’re graded by their rate of heat transfer. The pads I bought have a decent transfer rate, but aren’t up into exotic territory. (I got mine off of Amazon.) As it turns out they’re probably overkill for the job, but I’d rather err on the side of too cool than not cool enough.

Everything Heat Sinked

With both pads installed and everything loaded into the box, a small block of closed cell foam acts like a spring to keep the battery and the recorder pressed up against their respective pads.

Weatherproof Recording Box in the Field

Last weekend I took it out to an old cane haul road on the Hamakua Coast to record coqui frogs. Unfortunately the road was blocked off about a mile from where I wanted to record, so I had to set in a different location along the road. It looks like logging operations are about to start out there, so this may be the last time I get to record at that location. (The box is weatherproof, but it won’t stop a bulldozer!)

I had some issues with moisture causing noise on the mics early on in the evening, but overall the session went well. I used my SASS with EM-172 capsules for this. EM-172s aren’t typically all that sensitive to humidity, so I’m looking into why the mics glitched. So far I haven’t been able to reproduce it, but I might spend some time monitoring the next time I use this box just so I can hear if it’s happening again.

Meanwhile, here’s a long(ish) track from the test. It covers the sunset transition from primarily birdsong and insects to the coqui frogs dominating the soundscape. And there’s the occasional cow. (I really love the way cow calls reverberate through eucalyptus trees.)

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Alice Microphone – Switchable Voicing

Posted by Tom Benedict on 10/05/2017

Back when I built my first Alice microphone I intended to use it for field recording. I took it out numerous times, but compared to other microphones I already had it always seemed noisy. Some testing indicated it wasn’t noise, just over-sensitivity to the higher frequencies generated by even the slightest wind in trees. Homero Leal pointed out that Ricardo Lee had documented an EQ modification to the Alice circuit on the Yahoo! micbuilders forum that could tame some of the high end sensitivity, so shortly after that I modified both of my Alice mics.

A couple of months afterward I started looking into voice acting. I have no aspirations of changing careers at this point, but I’ve been reading to my kids for close to eighteen years now, and one by one they’re starting to leave the nest. By the end of the summer the only way I’ll be able to read to my oldest is if I record each session and email the file.

To be fair the style of reading I do is closer to voice acting than straight reading. I like to give each character a unique voice. I like to read each book as if it was an old-school radio drama. So I knew my foray into voice acting would wind up being more than just figuring out how to record the sound of my voice. I wanted to become a better voice actor.

But yeah, I also wanted to learn how to record my sessions to the best of my ability. The more I poked into the technical requirements, the more I realized the Alice microphones make really nice voice mics. And the more I played with my TSB-2555B Alice, the more I realized I might want to disable the HF EQ mod for certain voices.

So I asked Ricardo if I could wire his HF EQ mod through a switch, making it an option rather than a default. He said the circuit isn’t particularly noise sensitive, and that he didn’t think there would be any problems. In the end I picked a switch that let me have three configurations: no HF EQ, Ricardo’s HF EQ to make the mic sound more like a U87, and one more that I haven’t committed to yet. (I’ll figure out how to wire that once I figure out which voices I need to EQ for.)

The fun part about adding the switch to the BM-800 Alice was figuring out how to mount it. I went back to the 3D CAD model I made of the mic, added the switch, and found I could fit some aluminum angle across the mounting holes on the opposite side from the PCB.

The only problem with that plan was that the aluminum angle had to fit inside the body tube of the mic. The top needed to be round, and for it to blend with the rest of the microphone I needed the sides to be tapered, just like the Alice PCB.

There are plenty of ways to make profiles like this, especially if you employ the aid of a CNC machine tool. But part of the joy of making things, for me, is spending time with the tools, hands on the handwheels, coming up with ways to get exactly what you want.

Switchable HF EQ

I wound up machining a lathe fixture to cut the profile. The fixture mimicked the internal frame of the BM-800 microphone, complete with screw holes and taper. Once I’d drilled the holes in the aluminium angle on the mill, I bolted it to the fixture and chucked it up in the lathe with the compound slide set over the necessary 2.3 degrees. It worked like a charm.

The switch isn’t the most convenient thing in the world since I have to take the body tube off the mic to change its position, and since the M-S Alice uses both sides of the frame it’s not something I can apply to that mic in its current form. But for now I’m not planning to use the M-S Alice for voice, and changing the mic’s characteristics isn’t something I’d want to switch on the fly, anyway. I think it’ll work out ok.

I’m still working through the nightmarish acoustics in my house, but with the help of a number of voice actors who have been kind enough to answer my barrage of questions, I think I’ll eventually get that sorted as well.

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Weatherproof Recording Box

Posted by Tom Benedict on 07/05/2017

In earlier posts I’ve mentioned that I do most of my field recording by dropping off my gear and recovering it later. This works great for a lot of reasons, not the least of which is that I make noise constantly. By using the drop-and-recover technique, I can get as far away from my mics as possible.

Another advantage of this technique is that I’ve found it takes between fifteen to forty five minutes for wildlife to return to their normal behavior after they’ve been disturbed. Since I can record for upwards of 24 hours using this technique, this means I get lots of time in each recording during which I know the animals I’m hearing aren’t stressed.

The big drawback to this technique, though, is that when something goes wrong I’m not there to deal with it. The first time I left my gear out overnight it rained. I’d planned for it by draping my recorder with a plastic bag, but it was a stop-gap measure at best. I wanted something more permanent.

Months ago the nearby Costco began selling ammo boxes. My wife picked one up for me, figuring it would be a good starting point for a weatherproof recording box. I hemmed and hawed about what I wanted the box to do and how I wanted it to do it, and finally came up with a plan.

Weatherproof Recording Box

I wanted the box to be able to hold my recorder and an external battery pack, and provide weatherproof XLR connectors I could plug mics into without risking the integrity of the weather seal. I came up with a couple of pencil sketch designs, but none of my plans beat a piece of equipment that already existed: the weatherproof outlet cover.

Four Channels

I had to modify the outlet cover so it had an opening large enough for the four XLR panel connectors. I did the work on the Bridgeport, but similar results could be had by using any number of other techniques such as saw and file, Dremel or Foredom, etc.

The panel connectors are standard Neutrik parts. I picked up the rainbow colored grommets (also Neutrik parts) to provide additional weather sealing and to let me color coordinate the connectors on the inside.

Weatherproof Routing

Cables route in through the slots at the base of the box (in this case I only opened up one, though I’ll probably have to open up the other once I start recording four channel sound.)

It Closes!

Once the cover is closed the only way water can get into the connector area is to come in through the slot at the bottom of the box. It won’t stop immersion or flooding, but it stops even the horizontal rain we get here in town. (I had my kids spray the box aggressively with the garden hose before I trusted it to hold my equipment. Everything stayed nice and dry!)

Color Coordination

I lined the inside of the box with foam that I covered with leftover head liner material I had from when I replaced the head liner in my Civic. The foam panels are removable in case I change my mind or need more space inside, but for now they provide some measure of cushioning and no small amount of insulation for when conditions turn cold at night.

The inside connectors are also standard parts from Neutrik with boots that match the colors of the panel grommets. Unfortunately connector lengths caught up with me.

The Tight Fit

When I started this design I hadn’t planned on lining the box with foam. That came later once I realized how much my gear would rattle around if I did any hiking with the gear inside.

But once the foam was installed, the full-sized Neutrik connectors poked out so far I could only plug things in on one side of my recorder. Since the fourth channel is located on the opposite side from the other three on the DR-70D, this means I can’t actually plug in all four channels yet. At some point down the road I’ll replace all four with low profile right angle connectors from Cable Techniques, but for now I get two (well… three) channel sound.

I’d intended to build this box in time for the 2017 International Dawn Chorus Day. Unfortunately I missed by hours. IDCD 2017 happened at dawn this morning, and I just finished the box an hour ago.

Ah well…

Meanwhile I’ve got a setup that will let me do drop-and-recover recording, rain or shine, and keep my gear safe, sound, and dry.

UPDATE: I finally had the chance to answer one question I had about this design: With the foam lining, would I run the risk of overheating the gear in the box?

The answer is a qualified no. I put my recorder and my 10000mAh battery pack in the box with a temperature probe and closed the whole thing up. Ambient temperature was 21C. The temperature in the box rose steadily for the first hour, then began to roll off. After seven hours the temperature reached 32.5C with clear signs it would asymptote at or below 34C. That’s a delta of around 13C.

The DR-70D operating range is 0C – 40C, according to the Tascam web site. When I originally ran this test I thought this meant I was marginally safe. I’m pretty sure I was wrong. In the test I was measuring the air temperature inside the box, not the temperature of the electronics, which were considerably warmer than the air temp.

I came up with a fix for this and the connector issue, which I describe in the second part of this article: Weatherproof Recording Box – Part 2.


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Another Stab at Contact Mics

Posted by Tom Benedict on 07/05/2017

Several months ago I ran a bunch of tests on a contact mic to try to figure out the best (ok, best of several options) way to interface them to my recorder. It wasn’t the most exhaustive test, but it at least pointed me in a good direction.

Specifically I wanted to find which configuration had the best low frequency response. To that end the mic under test was a 35mm piezo element stuck to a subwoofer, and the tests consisted of running a frequency sweep through the subwoofer while I recorded the output of the contact mic.

I tried four configurations: 1 – direct TS plug-in, with all the high pass filtering that leads to. 2 – HOSA MIT-129 impedance-matching transformer. 3 – Alex Rice impedance matching preamp. 4 – Stompville impedance matching preamp.

It wasn’t the best subwoofer in the world so the data was lumpy, but a couple of things came through pretty clearly: Not surprisingly, the direct-plugin lost some of the low-end. The Alex Rice preamp is known to have noise issues, which also came out in the tests. As far as signal to noise went, the HOSA MIT-129 and the Stompville preamp were very close across the range of the test (10Hz-1kHz), but the Stompville had higher overall signal and required less gain out of the recorder.

My point in running these tests wasn’t to prove once and for all which setup was the best. It was just to get some direction for how to build my next round of contact mics. I decided to go with the preamp from Stompville and run with it.

Before going into just how I ran with it, here’s some background on the Stompville preamp: SmudgerD started the same place I did, with the Alex Rice preamp, but instead of just being frustrated with the noise floor, decided to redesign it, and then further refine it. The result is a very well thought out design. Even better, SmudgerD packed the whole thing onto a tiny PCB that fits on the back of a Neutrik XLR panel jack.

I bought two.

(But I wish I’d bought four.)

Then I stuck them in a box.

Contact Mic Preamp Box

The bottom of the box is tapped 1/4″-20 so I can attach it to the top of my DR-70D using the camera mount thumbscrew. Two of the Stompville preamps face out one side, and as soon as I buy another two they will face out the other side. The third face has a row of mini-XLR connectors for plugging in the contact mics themselves.

I was turned on to the mini-XLR connectors by Mo, who shared them in a comment on my EM-172 and XLR Plug article. I have to say these things are the cat’s pajamas. They’re small, they’re inexpensive, they have a positive lock, and they have the neat feature of having pin 1 make contact before the other pins. This ensures ground makes contact before the signal pins. I love ’em.

Unfortunately, right after I finished the box I was drawn into other things. So I only have two contact mics built so far. The first is the one that’s still attached to the subwoofer. The other is a prototype I built to test the preamp box in the field.

Prototype Contact Mic

It’s ugly, but it works remarkably well as long as you don’t apply any pressure on the center of the piezo. (This introduces a large DC offset.) The next rev, of which I’m building four, will be fully enclosed.

Just for grins I took the whole mess in to work to play.


– Tom

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Rest In Peace My Friend

Posted by Tom Benedict on 07/01/2017


5 May, 2010 – 6 January, 2017

Rest in peace, my friend

Can your tongue do THIS?!


Ember, Coned


Ember - Second Splint


Ember: Amputee


Edit Kitty


Ember - Done


Sunset Ember


Ember Sleeping - Close-Up


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(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.


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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