More bird experiments / October 27, 2018 by kelly heaton

I continue to explore circuits for bird song creation. I'm working my way through various schematics found on the Internet, testing them to hear how different parts and configurations sound. So far, most of the bird circuits I've built fall into the "chirping canary" or "depressive parrot" categories. Just prior to this log, I discovered another schematic to try -- and it's accompanied by a really helpful video by Mario Burriel Valencia aka @DJ Mystic https://youtu.be/W69VaPoPoVo

@DJ Mystic confirms what I have long suspected -- it's not only the shape of a waveform (sine, square, triangle, sawtooth, etc), or the component type (resistor, capacitor, transistor, etc), but the *specific make* of a component that can affect pitch, timbre, and loudness. This is especially true for transistors, and I have also seen variation in capacitors. ...Yes... I have read blogs by audiophiles discussing the pros and cons of specific parts for hi-fi equipment, but I didn't fully appreciate the importance of component specificity in low-cost sound generation. For some reason I assumed that since I work with cheap parts, the make wasn't that important. For example, I have thus-far thrown 2N3904 transistors at every problem they will solve. Now I realize the power of expanding my palette. Fortunately, I've got a friend coming down from the US and she's willing to bring a bag of electronics with her... so stay tuned for that excitement.

As for progress in the past few days, I bit the bullet and breadboarded a circuit with op amps. My attitude may seem weird considering that most synthesizer enthusiasts live and breathe op amps... but the dual power supply annoys me (and I've never gotten interesting effects with single supply op amps). Fortunately, some years ago, Bernie Hutchins gave me a useful schematic to convert voltage from a DC supply into a negative voltage of almost (not quite) the same magnitude. So if you have a 12 volt supply, you can produce negative 9-10 volts using a 555 timer and a handful of components. Please see my project files on Hackaday.io for this handy "Negative supply" circuit, or read about it on Electronotes.

The bird circuit that I built with op amps is described as "two canaries singing in a cage." You can find the schematic here: http://circuitos-de-electronica.blogspot.com/2007/10/canary-sound-simulator.html

I substituted a bunch of LM741s for the LM324s because I don't like building in tight quarters. You can see the resulting circuit in this video, where the "two canaries" are in the breadboard in the foreground (a previously built "transformer canary" is in the background):

I added some photocell resistors plus a few wires that you'll see me moving around (poor man's patch synth) to get variation in the circuit's behavior. It's pretty interesting, but maybe not worth the effort because there's a fair amount of complexity for sound effects that can be achieved with fewer parts. Still, I might make one of my electronic painting / sound studies with it because I like the aesthetic of crazy-complicated circuits.

Last but not least, here's a short video of a different bird circuit (the transformer one discussed in my previous log and shown in the background of the "two canary" video). I tested various capacitors and it's pretty cool the realistic bird sounds that you can achieve with such a simple component swap.

Still lots of work to be done.

New bird in town / October 25, 2018 by kelly heaton

I've temporarily relocated the physical form of Hacking Nature's Musicians to the other-worldly environment of Tortuga Escondida (near Akumal, Mexico) for a one-month fellowship on los musicos de la selva. Thankfully, my supplies made it through airport security and there's air conditioning to protect my electronic equipment against jungle humidity. Here's a photo of my bench showing a view of the jungle canopy and stairs to a roof deck with an amazing panorama over the electrically-charged ecosystem. (Giant scorpions occasionally grace my window screens but I have spared you that visual discomfort.)

My electronics bench at Tortuga Escondida near Akumal, Mexico. October, 2018

A few observations before I jump into the main content of this log: (1) Tortuga Escondida seriously resembles a research facility from the TV series Lost, so if I disappear you know what happened to me; and (2) the insects here are at least twice the size of their Virginian counterparts. Check out this insane Katydid!

Amazing giant Katydid in the jungle around Tortuga Escondida (greater Akumal, Mexico). October, 2018

Amazing as the insects are, I'm not studying musical bugs because what's most remarkable to me --coming here from Virginia-- are the myriad species of birds. I've decided to see what I can do with the analog electrical engineering of bird song.

As a starting point, I built a version of the classic, "chirping canary" used in kitschy artificial nature scenes. Check out my files on Hackaday.io for an annotated version of this schematic, which is based on audio transformer oscillation. Basically, the surge in DC power that happens when you first turn the circuit on is capacitively coupled across the transformer and continues to fluctuate thanks to a transistor switch. If you change (or remove) certain capacitor values, the circuit stops oscillating and makes an unpleasant tone that can be very loud due to the current gain across the transformer.

I've made a first informal video showing how the sound changes when different parts of the circuit are modified (apologies in advanced for some unpleasant beeps - don't wear headphones).

Next, I built a few astable multivibrators and connected them to various aspects of the sound-generating circuit in order to make the chirp sound more like a bird song. Some of my tests are documented in a second video that you can watch on Vimeo.

Watch the green LEDs (and follow the white wires) to get a sense for what the astable multivibrators are doing.

Birds are very clever singer-songwriters, so it's going to take a lot more work on tempo and pitch variation to get interesting songs. I plan to try numerous strategies to generate voice quality because I want to build a jungle of different bird circuits ranging from sparrows to whippoorwills to parrots to owls to a Resplendent Quetzal, relative of the legendary Mayan Plumed Serpent. If you have suggestions for circuits to try, I would be grateful.

So... not only do my bird electronics need work, I could use a new "avian speaker" design. It seems that piezo buzzers are better suited to insects, while 8 ohm speakers have higher bird fidelity. Initially, this observation puzzled me (and I'm still not clear) but I got some useful clues from the ingenious musician, Nicolas Bras. It's material physics: the thin, metal vibrations of a piezo disk have more in common with the chitin instrumentation of an invertebrate than the fleshy air bladder and vocal chords of a squawking bird. Some insects do force air through a membrane, like living kazoos, but crickets rely heavily on the idiophonic effects of leg or wing rubbing. The sound made by an idiophone is quite different than that of an aerophone or membranophone, like hitting a cymbal versus blowing through a reed, the latter of which happens when a bird forces air through its vocal cords. I searched the web for homemade instruments that behave like an aerophone with a membrane and found this cool "membranophone" video by tachionics.

As I did with my "insect-like" piezo, I'd like to build an electronically actuated speaker that has material properties more in common with a bird. I've got various 8 ohm speakers that are working for now, but I suspect that there's a better design to be made -- or at least some cool insights to discover in the process of trying. Again, your suggestions are greatly appreciated!

Stay tuned.