The View Up Here

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

Posts Tagged ‘Stereo’

Building the MS Alice Microphone – Part 2

Posted by Tom Benedict on 23/11/2016

This is the second half of a two-part article describing my build of the mid-side Alice microphone, following the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. In Part 1 of this article I ran through how I was planning to build it (mostly following the same steps I used in another two-part series I wrote about another of Jules’s Instructables, Modify a Cheap LDC Condenser Microphone, namely: BM-800 Microphone Conversion Part 1 and Part 2.) I also covered my design for the saddle and post that holds the three capsules in the particular orientations required for Jules’s MS microphone build. (Jules used a different method, using PVC pipe, which you’ll see in his Instructable if you decide to build one of your own.)

Since writing Part 1 all the bits and pieces came in. I was eager to see how the 3D printed saddle and post turned out, and how well the TSB-165A capsules fit.

M-S Alice Capsule Saddle and Post - Unpopulated

I designed the cavities for the capsules at-size, meaning I didn’t leave any slop for fit. The plastic Shapeways uses to make their least expensive printed parts is described as “strong and flexible”. I took them up on that, figuring the part would flex enough to allow the capsules to snap into place. It worked like a charm.

M-S Alice Capsule Saddle and Post - Populated

The fit is snug, but not snug enough to hold the capsules in use. As with my first Alice, I glued the capsules into the saddle with E-6000 adhesive.

I’m a little disappointed with the handling noise on my first Alice mic. I chalk some of that up to the metal saddle and post, but some of it I chalk up to the relatively stiff wire I used to connect the capsule to the PCB. It was stiff enough that manipulating the wire wound up breaking off one of the ground tabs from the TSB-2555B capsule I used on that mic. Rather than repeat that experience, and in an effort to reduce conduction paths for handling noise, I gutted some of the Mogami cable I use for all my microphone projects and used the wires to connect the capsules. (NOTE: It didn’t actually affect handling noise that much. After thumping various bits of the mic, I’ve come to the conclusion the dominant frequency of the handling noise is driven by the resonant frequency of the mesh in the headbasket.)

I already had two Pimped Alice PCBs built, tuned, and ready to go for this project. The remaining steps were to screw one board onto each side of the mic frame, solder the capsule wires to the boards, solder the four 0.022uF capacitors between the ground pin (pin 1) and the remaining pins of the XLR connector (2, 3, 4, and 5), and to solder wires between the XLR and the PCBs.

M-S Alice Internals

Since I oriented the two capsules of the figure-eight mic side-by-side, they won’t fit inside the headbasket with the foam liner in place. So I stripped the foam out before closing up the mic.

The very last step was to build the 5-pin XLR to dual 3-pin XLR splitter cable. There are a number of ways I could’ve done this, but I followed (mostly) Jules’s build on the cable as well, using separate Mogami lavalier cables for each channel. This is a wonderfully floppy wire, and does an excellent job of reducing handling noise transmitted through the cable.

The one change I made to Jules’s design was to jacket the central eight feet of cable in a woven sleeve to keep it from tangling.

M-S Alice Patch Cord

I left the last foot and a half at each end loose, though, to take advantage of the wire’s floppiness. (Hey, that’s actually a word spellcheck recognizes!)

And at long long last I’m able to play with mid-side recording and compare it against my EM-172 based SASS.

SASS vs. M-S Comparison

Big big thanks to the following for making this all possible:

  • Jules Ryckenbusch – for writing the two Instructables that got me going on these microphones
  • Homero Leal – for coming up with the PCB layout for the Alice boards used in Jules’s Instructables
  • Scott Helmke – for designing the Alice circuit in the first place
  • Ricardo Lee and all of the above – for their endless patience with all of my questions and what-ifs
  • Dr. Ing – for designing the Schoeps CMC-5 in the first place, without which none of this would exist

For my own contribution, here’s the link to the MS Alice capsule saddle and post on Shapeways. I’ve listed these at-cost, with no mark up (meaning I don’t see a dime of the 5.35 USD price tag at the time of this writing – labor of love).

Have fun recording!

Tom

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Posted in Audio, Engineering | Tagged: , , , , , , , , | 4 Comments »

Building the MS Alice Microphone – Part 1

Posted by Tom Benedict on 11/11/2016

This is a short pair of articles that glosses over most of the details of how I’m building a self-contained mid-side (MS) Alice microphone into a Neewer NW-800 microphone body. Part 1 covers most of the design and preparation, and Part 2 will cover the build.

The reason why this pair of articles is so brief is that most of the nitty-gritty was already covered in another pair of articles: BM-800 Microphone Conversion Part 1 and Part 2. The major differences between that microphone and this one are a change in capsules (Transsound TSB-165A instead of a Transsound TSB-2555B), the number of capsules (three instead of one), the number of Pimped Alice boards (two instead of one), and a change tof XLR connector (5-pin rather than 3-pin).

With the exception of how I’m planning to mount the capsules, all of this follows the Instructable written by Jules Ryckenbusch: Build the MS Alice Stereo Microphone. That’s the real reference for this build, so if you decide to build one of these yourself be sure to follow Jules’s notes.

The easy stuff first:

When I built my first Alice microphone I built three PCBs rather than just the one I needed, so I already have two Pimped Alice boards ready and waiting in the wings. I was on the fence whether to build a second mic around a TSB-2555B capsule or go straight to the MS Alice. After some recent field tests, I decided to commit the two boards to an MS Alice.

Jules pulled a neat trick for getting two signals out of a single XLR connector: use a different XLR connector! In his build he replaced the 3-pin XLR that came with his BM-800 microphone with a 5-pin. The two outputs share a common ground, but have independent signal pins. I’m following this part of his plan to the letter. (As a side note, this also gives me a spare 3-pin XLR connector to use when I finally build out my parabolic mic. New project in the works!)

The only things left to do were to order three TSB-165A capsules (done) and to figure out how to mount them.

Jules has a nice tutorial on how to build a 3-capsule saddle out of PVC pipe, but I had so much fun machining a custom saddle for my TSB-2555B capsule, I couldn’t pass up the opportunity to massively over-complicate life by designing a custom saddle for the MS Alice as well. Here’s what I came up with:

MS Alice TSB-165A Capsule Saddle

Which looks neat and all, but would be stupidly difficult to machine. It’s possible, provided you got rid of, or at least filleted the inside corner between the two side capsules, but it wouldn’t be fun. And since this is all about fun, I cheated. I sent it off to be 3D printed out of nylon. (If this pans out and there’s any interest, I’m happy to make the 3D model available for other people to print.)

So now I’m back to playing the waiting game. I’ve got parts coming in from Redco Audio (5-pin XLR to dual 3-pin XLR splitter cable), Mouser (smaller capacitors for the Alice boards to address the space constraint issue I ran into), Amazon (Switchcraft 5-pin XLR connector, NW-800 body, and associated doodads), JLI Electronics (three TSB-165A capsules), and finally Shapeways (the 3D printed mic saddle).

I’ll write the second half of this series once all the goodies show up.

Tom

Posted in Audio | Tagged: , , , , , , , , | 3 Comments »

SASS and ORTF Side-by-Side

Posted by Tom Benedict on 09/08/2016

Or top and bottom, rather.

I had the opportunity to stick my SASS rig and my newly minted ORTF bar on the same mount, one right over the other, and use them to record coqui frogs in a eucalyptus forest on the Big Island of Hawaii.

Of course whenever you record in a forest here you also get insects.

And if you happen to be within a hundred yards of a bunch of… dinosaurs? You also get them.

And the rain.

Ok, just a bunch of stuff. Anyway, here’s the recording. It’s an A-B test, switching between SASS and ORTF at thirty second intervals with a two second cross-fade.

My take: The two are different. (Well duh!) They provide different sounds. Neither one is “right” to my ear, just… different. But I’ll let you decide for yourself.

Tom

P.S. No I didn’t say which is which in the recording. What would be the fun of that?

Posted in Audio | Tagged: , , , , , , , , | 2 Comments »

A Self-Contained Stereo Field Recording Setup

Posted by Tom Benedict on 16/06/2016

A project I’ve been working on more or less led me by the nose toward a type of field recording I really enjoy doing. The project requires relatively long recordings of an ambient soundscape – an hour or longer. The recordings must be in stereo, and ideally serve to put the listener in the soundscape as completely as possible.

Because I can never really stop making noise, especially now that I’ve developed some rather energetic motor and vocal tics, the only way I’ve been able to pull this off is to set up my gear, leave it for an extended period, and recover it later. This drop and recover technique works great for these extended soundscape recordings. But because I often have to hike in for an hour or more to reach the locations I record in I’ve tried to shrink the setup as much as possible, resulting in a relatively compact arrangement. Here’s what I’m using at the moment:

Self Contained Stereo Recording - Front

It’s a self-built pseudo-SASS microphone array sitting on top of a vibration isolator that was made for attaching cameras to multirotors, which is then attached to my Tascam DR-70D recorder.

The vibration isolator took some modification to make it work for this application. I added a plate to the bottom that has a 1/4″-20 threaded hole in it. This lets it mount to practically any tripod or light stand, or to the top of my DR-70D using the camera attachment that came with it. The top of the mount had a 1/4″ through hole in it, but I had to make a big aluminum thumbscrew so I could thread it onto my DIY-SASS. It’s barely visible between the rubber balls on the shock mount in the photo above.

Self Contained Stereo Recording - Rear Quarter
In order for the shock isolator to work well I needed to use very flexible XLR cables to connect the mics to the recorder. And to keep things compact I needed them to be short. These are two things that make for some really hard to find cables. So like most of my gear I rolled my own.

The connectors are all from Neutrik and the cable is some leftover Mogami cable I had from building other sound bits. I really like the right angle female Neutrik connectors. They’re just as easy to use as the straight variety, and you can set the angle at which the cable comes out of the plug when you build the cable. I set mine to come out 45 degrees to the right to make the cable run a little cleaner and to clear the controls on my recorder.

Self Contained Stereo Recording - Back

The whole thing acts like a big wooden bobble-head doll. There’s not a lot of damping in the isolator, just a lot of spring, so once you thwack it it bounces around for a while. I’ll have to see how that works out in the field. Just testing indoors, though, the isolator does a good job of minimizing coupling between the tripod legs and the microphones. This should help minimize noise from grass, twigs, and branches that tap against the tripod legs during a recording. (This naturally occurring handling noise has ruined several recordings I’ve made in the past.)

The one obvious problem with this setup is that there’s no real way to monitor while recording. But since I’m leaving my gear in the field and walking away from it, it’s not really an issue for me.

I’m still working on wind protection. For light wind I have a lycra slip cover that goes over the pseudo-SASS. But for stronger wind I’ll need something more involved. (Hey, more problems to solve! My favorite!)

Tom

Posted in Audio | Tagged: , , , , , | 8 Comments »

Stereo Aerial Photography and False Color

Posted by Tom Benedict on 26/06/2009

It’s always fun to see what can be done with aerial photography: large stitched panoramas, Photosynths, 3D modeling, 2D maps.  One technique that KAP lends itself to particularly well is stereo aerial photography.

With an airplane, stereo photography is typically done by pointing the camera 90 degrees to the direction of flight, and taking a succession of pictures as the airplane flies across the landscape.  Careful choice of frame rate, airspeed, and altitude yields good results.

With a kite, a similar technique can be used:  Point the camera 90 degrees to the kite line, start the shutter going, and carefully walk backwards.  The kite will quickly settle into a stable flight angle with the increased apparent wind speed from the walking, and a nice steady stream of pictures is the result.  This is an example from a recent flight over the contact between two lava flows on the Big Island of Hawaii:

Lava Stereo Pair - True and False Color

The top two pictures are the natural color images as they came off the camera.  The bottom two require more explanation:

Another technique I’ve used with aerial photography is to apply false color techniques to boost certain details, certain colors, or to change the contrast of the image so that particular features will catch the eye.  Most of my experimentation along these lines has been done using an image manipulation program called ImageJ, and a plug-in called DStretch.  ImageJ is a general purpose image manipulation program written in Java.  DStretch is an implementation of the principal component algorithm for contrast stretching that was written by Jon Harman.  It was originally written for bringing up faint details in pictographs, but it has proven to be useful with aerial imagery as well.

In order to get a sense of scale of the image, the thin yellow line in the top pair is a three-section 25′ painter’s pole thath as been collapsed to its shortest length.  My flying partner and I were using it to lower a camera into one of the holes we found in the lava in order to explore the inside.

This probably isn’t the best example of either technique, but it’s the first time I used them in combination.  At some point I’ll write a more in-depth article about building stereo pairs, and a second article about the use of ImageJ and DStretch with aerial photography.  In the meanwhile, enjoy.

Tom

Posted in Kite Aerial Photography, Photography | Tagged: , , , , , , , , | 1 Comment »