Logic Noise: Filters and Drums

Filters and Drums

Logic Noise is an exploration of building raw synthesizers with CMOS logic chips. This session, we continue to abuse the 4069UB as an amplifier. We’ll turn the simple unity-gain buffer of last session into a single-pole active lowpass filter with a single part. (Spoiler: it’s a capacitor.)

While totally useful, this simple filter is a bit boring and difficult to make dynamic. So we’ll look into an entirely different filter, the Twin-T notch filter, that turns out to be sharp enough to build a sine-wave oscillator on, and tweakable enough that we’ll make a damped-oscillator drum sound out of it.

Here’s a quick demo of where we’re heading. Read on to see how we get there.

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3D Spectrum Analyzer uses 1280 LEDs

One of [Dooievriend]’s friends recently pressed him into service to write software for a 3d spectrum analyzer/VU that he made. The VU is a fairly complex build: it’s made up of 1280 LEDs in a 16x16x5 matrix controlled by a PIC32 clocked at 80MHz. [Dooievriend] wrote some firmware for the PIC that uses a variation on a discrete Fourier transform to create a 3D VU effect.

j6v2i When [Dooievriend] set out to design the audio analyzing portion of the firmware, his mind jumped to the discrete Fourier transform. This transform calculates the amplitude in a series of frequency bins in the audio—seemingly perfect for a VU. However, after some more research, [Dooievriend] decided to implement a constant Q transform. This transform is very similar to a Fourier transform, but it takes into account the logarithmic way that the human ear interprets sound.

[Dooievriend] started implementing the constant Q transform using an interrupt-based sampler, but he quickly ran into issues with slow floating-point math on his PIC32 (which doesn’t have a hardware floating-point unit). Thankfully he rewrote his code using fixed-point math, and the transform runs nearly real-time. Check out the video after the break to see the VU in action, and a second video that gives some details on the hardware build.

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The Hard Drive MIDI Controller

[shantea] builds MIDI controllers, and after a successful first endeavor with a matrix of buttons and knobs, he decided to branch out to something a little bit cooler. It’s called Ceylon, and it’s effectively a turntable controller built from an old hard drive.

As a contrast to the first MIDI controller, this would be a stripped-down build, with just three faders, LEDs for eye candy, a pair of pots for gain control, and a hard disk surrounded by six anti-vandal buttons. The hard disk is the star of the show, acting as a rotary encoder.

When manually spun, the hard disk generates a few phases of sinusoidal waves. The faster you spin it, the higher the amplitude and frequency. These signals are far too weak to be sampled directly by a microcontroller, and for digital control – as in, MIDI – you don’t need to read the analog signals anyway. These signals were turned digital with the help of an LM339 quad comparator. With two of these comparators and signals out of the hard disk that are 90 degrees out of phase, quadrature encoding is pretty easy.

The software for this MIDI controller is based on the OpenDeck Platform, a neat system that allows anyone to create their own MIDI controllers and devices.  It’s also a great looking board that seems to perform well. Video below.

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Arduino Synth Guitar Really Rocks

[Gr4yhound] has been rocking out on his recently completed synth guitar. The guitar was built mostly from scratch using an Arduino, some harvested drum pads, and some ribbon potentiometers. The video below shows that not only does it sound good, but [Gr4yhound] obviously knows how to play it.

The physical portion of the build consists of two main components. The body of the guitar is made from a chunk of pine that was routed out by [Gr4yhound’s] own home-made CNC. Three circles were routed out to make room for the harvested Yamaha drum pads, some wiring, and a joystick shield. The other main component is the guitar neck. This was actually a Squire Affinity Strat neck with the frets removed.

For the electronics, [Gr4yhound] has released a series of schematics on Imgur. Three SoftPot membrane potentiometers were added to the neck to simulate strings. This setup allows [Gr4yhound] to adjust the finger position after the note has already been started. This results in a sliding sound that you can’t easily emulate on a keyboard. The three drum pads act as touch sensors for each of the three strings. [Gr4yhound] is able to play each string simultaneously, forming harmonies.

The joystick shield allows [Gr4yhound] to add additional effects to the overall sound. In one of his demo videos you can see him using the joystick to add an effect. An Arduino Micro acts as the primary controller and transmits the musical notes as MIDI commands. [Gr4yhound] is using a commercial MIDI to USB converter in order to play the music on a computer. The converter also allows him to power the Arduino via USB, eliminating the need for batteries.

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Kitsch-Instrument Pulls a Sonata out of your Dishware

Remember those childhood memories of your grandmother telling you to stop hammering away at her pots and pans? Odds are pretty good that the last time you struck a beat with her dishware, you had a few more years to go before you understood tempo and rhythm. Now that we’re a bit older, [Jiffer Harriman] invites us to return to our kitchen armed not only with those childhood memories, but also a with the Kitsch-Instrument: a suite of solenoids, a controller, and a software pipeline to algorithmically turn your kitchen into a giant percussion instrument.

The Kitsch-Instrument is a modular music system that enables the user to pull a percussive pattern out of his or her everyday kitchen utensils. The percussion hits come from a series of mosfet-driven solenoids that can be fixed onto plates, cups, and other everyday items through a variety of clips. These solenoids are collectively driven by two stacked custom Arduino shields that are, in turn, driven either by hand with a button-interface, or algorithmically with a pattern generated by the graphical programming language, Pure Data.

In designing this project, [Jiffer] and his team intended to bring not just a musical tool to young tinkerers. They also aimed to help educate these young minds with multiple entry points into their project. For top-level users, adding buttons is almost as easy as plug-in-and-play. For experienced circuit designers and tinkerers, the entire project is open source with the board layout and software available for download. Overall the project can be explored from lower and lower levels while still retaining its functionality as a musical interface.

If you suspect that this project seems to have that same whimsical sense as the Auto-Meter-Reader Feeder, you’d be right! [Jiffer] and [Zack] hail from the same lab at the University of Colorado. We’re excited to see what upcoming beats will arise from a truly off-the-shelf symphony.

via the [Tangible Embedded and Embodied Conference]

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Play Music with your Painting Using Teensy

[sab-art], a collaboration between [Sophia Brueckner] and [Eric Rosenbaum], has created a touch-sensitive musical painting. Initially, basic acrylic paint is used for the majority of the canvas. Once that is dry, conductive paint is used to make the shapes that will be used for the capacitive touch sensing. As an added step to increase the robustness, nails are hammered through each painted shape and connected with wiring in the back of the painting. These wires are then connected to the inputs of a Teensy++ 2.0, using Arduino code based on MaKey MaKey to output MIDI. The MIDI is then sent to a Mac Mini which then synthesizes the sound using Ableton Live.  Any MIDI-processing software would work, though. For this particular painting, external speakers are used, but incorporating speakers into your own composition is certainly possible.

A nice aspect of this project is that it can be as simple or as complex as you choose. Multiple conductive shapes can be connected through the back to the same Teensy input so that they play the same sound. While [sab-art] went with a more abstract look, this can be used with any style. Imagine taking a painting of Dogs Playing Poker and having each dog bark in its respective breed’s manner when you touch it, or having spaceships make “pew pew” noises. For a truly meta moment, an interactive MIDI painting of a MIDI keyboard would be sublime. [sab-art] is refining the process with each new painting, so even more imaginative musical works of art are on the horizon. We can’t wait to see and hear them!

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Turning a Cadenza into a Finishing Move

What do you get when you mix dueling pianos with a 2D fighting game? Undoubtably some complex controls, but also an awesome platform for showmanship! The “Sound Fighter” installation by artists [Cyril] and [Eric] was built with the exact intention that two opposing parties could duke it out in a Street Fighter match with their piano playing abilities mapping into attack combos and dragon-punches.

In order to turn a piano into a glorified arcade stick, [Cyril] and [Eric] would need a way to register when and what notes were being played and then translate that data into commands for the fighting game itself. To start, they did their homework on the inner workings of different piano types. Whatever digital augmentation they were to design would have to work without inhibiting the piano’s function.

There were many possible methods of registering when the piano was being used and though several would have worked for their intended purpose, it took writing down and discussing the pros and cons of each sensor before they made a decision. Some of the options they considered included pressure sensors for the keys themselves, accelerometers to detect the movement of the individual hammers within the piano, and even a microphone to computationally analyze the sound heard from either instrument. In the end they chose to implement small and accurate piezo knock sensors tethered to the internal mechanism of each key. These could register both faint and strong notes when played without altering the natural sound of the instrument.

fighterPiano_2

After deciding on a Street Fighter iteration for the PS2 to develop the rest of the project around, they had to play the actual game a bit to get a feel for the command list of moves. They wanted to conceive of a way to map the notes played to the controller, but not in the direct “key to button” sort of way. The idea was that if someone was good at playing piano, they would also be good at executing moves in game. So they had to sort out how groups of notes and chords would translate into moving the character or attacking.

I highly suggest checking out their in depth play-by-play as they built the installation from the ground up. In addition to being fascinating (they prepared this project in a fight against time for the reopening of a historical site in Paris), you’ll find that everything they developed is opened source. The completed installation is as awesome as it sounds. You can see it in action in an actual duel below:

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