Boing Boing

How to Make Sound Waves from Moonlight

Ethan Persoff

Hello and welcome back to Spoken Word with Electronics. This week we discuss the Moon. The silent glow-in-the-dark ball in the sky! The Moon is cool. Contrary to the Sun, you can stare at the Moon as long as you'd like. Staring at the Moon is even good for your mental health. (To make a pun on introspection, it is a source of reflective light, after all.) So this week we discuss how to convert Moonlight, which is heavily varied, shadow-casting, and subtle, into similarly variable voltage that can play synthesizers.

    Items Needed

  1. You will need a Moon:


    For these instructions to work you will need access to Moonlight in some fashion. People living in cities or cloudy regions will have more of a challenge for this. If Moonlight is a rarity, perhaps this is something you can anticipate and schedule, or even take a road trip to a good Moon spot, using this recording method as a justification for the excursion. People who take solstices seriously might value this Moonlight World Map, as well.

    But fear not, Moonless folk! The included tutorial on track two includes instructions on equally good experiments, using household lamps, dimmers, and strobe lights. But, if you're specifically wanting to generate waveforms out of Moonlight, there's few ways around this: You need a Moon. Ideally a bright one.

  2. Of course, some places have inadequate Moon coverage. Even on a cloudless night, light pollution might make your local Moon too dim or even unviewable. To address this, if you're in a small enough population, you can advocate to become a Dark Sky town. There's proof of this being successful and oddly politically even in terms of debate. Many varied opinions seem to agree on liking clear dark skies. Here in Texas, the city of Dripping Springs has achieved an Outside Lighting Ordinance to keep the lights off or dim. (Yes, lights are needed for safety, but not all bright night lights in a city are necessary) Who knows, maybe you can achieve something similar as a rewarding piece of eco-activism? The International Dark Sky Organization is a great place to start with resources and tips.
  3. ADVISORY: Fake Moon fragments for sale on the Metaverse do not count as a real Moon. When in doubt of Moon authenticity, ask a frog.
  4. In the audio for this episode we use Moonlight in track one. You'll hear it modulating the audio on a field recording of crickets and controlling numerous cascading parameters of the music underneath. I had two sensors, each on a cable, which I'll describe below.
  5. I held the green cable (which is long, note how much it's been wound up) and wandered around, and laid the red cable on the ground. Here they are for reference:

    Green Cable

    Red Cable

  6. The method of Moon Waveform Extraction (M.W.E.) that we'll be using is through use of Light Sensors to convert light into Control Voltage.
  7. Light Sensors have a bunch of great names: Photocells, Photo Resistors, Photo Conductive Cells. With the equipment used in this exercise, the the Sensors will detect pure darkness as zero and a variation to the brightest of light at five. (Advanced learning: They also provide a simultaneous flipped output, equal to negative five to zero.)
  8. Cool word you've probably never heard of before. The method of light to voltage conversion you'll be using is called Optoelectronics!
  9. As for sound created from this process, listen for a bell. A bell is generated by Moonlight hitting a leaf (captured by the green cable) which was bouncing in the wind so the bell was triggered in rhythm. Another ambient noise is generated by five minutes of Moonlight beaming down on some grass (red cable), triggered to a cloud floating over the Moon like a subtle filter.
  10. The tools we'll use for this exercise are two eurorack modules: The Doepfer A-179-2 and the ADDAC ADDAC308:

    Light to CV Modules

    Both of these modules do the exact same primary thing: They are both Light to Control Voltage modules.

    Neither of these modules make sound; rather they provide voltage to adjust other synthesizer modules. In this example, the Moonlight will shift in tone and hue and they'll track it and send positive and negative voltage out to another synthesizer module, making a hazy nice shifting ambience.

    11. A Light to CV module works with sensors to convert a measurement of light into an output of measured voltage.

    Basics: A completely dark light source (or absence of light) would mean no voltage output, while a completely bright light source would trigger an output of 100%. If you think of something as varied as light from the Moon during an evening, these variations can be extremely subtle, and both of these sensor modules allow for tuning the sensitivity, gain, and response of the sensors, allowing for a cascade of percentages of response. But they offer slightly different functions on how this voltage is processed and output; so I suggest they work best as a pair.

    Let's compare them:

    Patching for the Moon

  1. The dials for each of these modules are nicely simple and self-explanatory. Each dial, from sensitivity, gain, threshold, and offset, is a means of amplifying, attenuating, and fine tuning how the light source is detected. Both modules provide LEDs that indicate how the light is being perceived by the module, too. A good test is to simply hold a sensor up to a light and then cover your hand over the sensor. You should see all the LEDs go dark when no light is available to the sensor.
  2. The patch cables shown above arrive with adapters attached. These are really smart designs that add a simple LDR sensor onto one end of patch cable. The ADDAC offers this as a kit, as well, and you can see how easy it is to make your own extra sensors with two dabs of solder. (See page seven of these kit instructions) – Both the Doepfer and ADDAC models arrive built and with their own sensors. The Doepfer sensor is shown on the green cable above.
  3. Swapping out sensors: It is easy to plug these cables into the sensor inputs on each module. You'll insert the red TS cable into the "LDR input 1" of the ADDAC and the green TS cable into the "ext. Sens" input of the Doepfer. (Oddly there is no LDR input 2 on the ADDAC, so I'm not sure why they numbered it on the label.)
  4. On a full moon night, we then connected the four CV outputs and the one GATE output of these modules to the pitch, gate, and filter input of our portable synthesizer. Extending the sensors to light of Moon provided a high pitched sound, which was then tuned down with the dials on each panel to a variable tone. Shadows and scattered light was tuned to be slightly brighter than a low rumble.
  5. Remember that the Moon is an inspiring very cool thing. Don't be surprised if your mood changes while recording. Perhaps the Moon will sense the two of you communicating and provide a surprise or two in the way of your future thought or decision making! Repeat these Moon nights as needed.
  6. What's truly great is you might have a memory of the night getting very bright for a second, or maybe a gust of wind will send some dancing shadows over the sensors. You will hear this in the recording. The moments of this audio will be in code to your experience and might become more meaningful to you than a basic video recording.

    Going Portable

  1. To go outside for your Moon recording requires a portable eurorack case. I can confirm a small travel case like the Doepfer Mini Case works great with these two sensor modules. You might want to also bring a small field recorder with you to capture any ambience of the outside traffic, insects, people, or even the wind. The voice recorder on your phone works fine. You'll want a long extension cable for power. For the recordings in this show, I took a long extension cable out a window. You can read discussions on battery powered eurorack, here's an example.
  2. The two modules shown above create no sound. They instead provide control voltage signals, so you'll need other modules to be affected by the signals they send out with a proper CV input to make noise. If you don't have a fully developed eurorack case, I suggest an off-the-shelf piece of equipment. The Moog Mother 32 with its numerous CV inputs would be great for this exercise. But if you already have a eurorack case assembled there's lots of other voices that work very well. (You know what you have.)
  3. If you're intending to make a portable case, do understand that a Doepfer Mini Case has a really low amount of available power. I limit whatever I put in mine to a combined 150mA. If you're using any digital modules (ones with screens, etc) it's likely the Mini Case won't adequately power it.
  4. No matter what a case is rated for, you want to avoid stressing out the power supply, so a good rule of 75% max is often the way to go. So if a case is rated for an amp, don't put anything more than a combined 750mA inside of it. You can get an accurate reading of your power consumption with a Joranalogue Test 3. Observe the Peak mode of the Test 3 to let you know the full consumption of a module, which can fluctuate or spike on power on.
  5. Another good portable case (with more robust power options) are the 4MS Pods series. They are limited by the available depth of the case, however. So be sure to look for terms like 'skiff friendly' when planning modules for something like the 4MS (or just check the millimeter depth of the module to the case)

    Show Notes

  1. Nasa has a fantastic section on their website completely devoted to discussing the Moon. This perfect URL: https://moon.nasa.gov/
  2. Be sure to visit their section on Tides, describing relationship of the Earth and the Moon, and how it affects our oceans. Don't leave without checking out the work of Nasa illustrator Vi Nguyen, who is credited with this entire five section Moon Earth Gif. I could calmly watch these for hours. Look for the tiny human on slide three!
  3. I can't mention the Moon without mentioning Frogs. We have frogs outside near us and it has been amazing to observe how their moods change around a full Moon. Frogs often sing at the Moon. But they also meditate and seem less frightened around a full Moon. There's some communication going on there that's pretty wild.
  4. A group of frogs is called an Army. But a group of male frogs seeking sex is called a chorus!

    5. SWWE # 76: "How to Make Sound from the Moon"

    Ethan Persoff is a sound designer based in Austin Texas. He likes lists. You can subscribe to Spoken Word with Electronics via 1) Bandcamp and 2) most podcast services.

Exit mobile version