Turning A MicroKORG Into A MicroKORG S With This Speaker Mod

June 5, 2020 by Maya Posch 11 Comments

When [Michael Wessel] bought his MicroKORG synthesizer/vocoder, he felt less than amused when two years later the MicroKORG S was released, with the ‘S’ standing for ‘sound’, apparently, for the 2+1 speaker system that was added to it. Undeterred, [Michael] figured out that both synthesizers are similar enough that one could likely add a similar speaker system to the original MicroKORG.

The similarities between the two products become apparent when one compares the original with its successor, with the latter seemingly mostly adding said speakers and more presets, along with a snazzy new exterior. (Although the 1970s styling of the original may have more fans.) As the embedded video shows, this mod is fairly clean.

At the core of this mod is a PAM8403-based class D amplifier board. The PAM8403 is a 3 W audio amplifier, originally produced by Power Analog Microelectronics (now Diodes). While not an amazing amplifier, it lends itself well for battery-powered applications like the MicroKORG. Rounding out the build is a 7805 linear regulator to get 5 V for the PAM8403, a few filter capacitors, a switch to turn the speakers on/off, and of course the speakers.

Although there’s quite a bit of space in the enclosure, most speakers tend to be large enough that this can be a bit of a squeeze. [Michael] found some low-profile 20 W full-range speakers that seem to work well for this purpose. To finish wiring this up, all it takes is a hole saw and a way to get the audio output from the MicroKORG.

In this mod, [Michael] opted to get the audio from the output jack on the back, but for a cleaner result it probably could be wired straight into the on-board header.

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How Did They Get Sampled Sounds From An SN76489 8-bit Sound Chip?

June 5, 2020 by Jenny List 23 Comments

If you were lucky and had well-off parents in the early 1980s, your home computer had a sound chip on board and could make music. There were a variety of chips on the market that combined in some form the tone generators and noise sources of a synthesiser, but without the digital-to-analogue converters of later sound chips designed for sampled audio. They gave birth to chiptune music, but that was all they were made to do. The essence of a hack lies in making something perform in a way it was never intended to, and some game developers for the Acorn BBC Micro had its SN76489 producing sampled audio when it should never have been possible. How did they do it? It’s a topic [Chris Evans] has investigated thoroughly, and his write-up makes for a fascinating explanation.

So, how can a set of audio tone generators be turned into a sampled audio player, and how can it be done when the CPU is a relatively puny 6502? There’s no processor bandwidth for clever Fourier transform tricks, and 1980s tech isn’t set up for high data bandwidths. The answer lies in making best use of the controls the chip does offer, namely frequency and volume of a tone. A single cycle of a tone can be given a volume, and thus can be treated as a single sample of an unintended DAC. By using a tone frequency well above the audio range a suitable sample frequency can be found, and thus an audio stream can be played. The write-up has links to some examples in an emulator, and while they’re hardly hi-fi they’re better than you might expect for the hardware involved. Still, even at that they don’t approach this amazing 48kHz playback on a Commodore 64.

Header: SN76489, on a Colecovision console motherboard. Evan-Amos / Public domain.

Pulling Data From News Feed Telemetry

May 31, 2020 by Jenny List 7 Comments

We are used to seeing shots from TV news helicopters every day, they are part of the backdrop to life in the 21st century. But so often we hear them overlaid with studio commentary, so it’s interesting to hear that their raw audio contains telemetry. It caught the attention of [proto17], who took some audio pulled from a news helicopter video and subjected it to a thorough investigation to retrieve the data.

The write-up is at a very in-depth level, and while there’s an admission that some of the steps could have been performed more easily with ready-made tools, its point is to go through all steps at a low level. So the action largely takes place in GNU Radio, in which we see the process of identifying the signal and shifting it downwards in frequency before deducing its baud rate to retrieve its contents. The story’s not over though, because we then delve into some ASCII tricks to identify the packet frames, before finally retrieving the data itself. It still doesn’t tell you what the data contains, but it’s a fascinating process getting there nonetheless.

It’s easy to forget that GNU Radio has signal processing capabilities far beyond radio, but it was the subject of a fascinating Superconference talk. We even jumped on the bandwagon in the non-foolish part of our April Fool this year.

Homebrew Binaural Microphone Lets You Listen Like A Human

May 31, 2020 by Dan Maloney 22 Comments

We humans may not have superpowers, but the sensor suite we have is still pretty impressive. We have binocular vision that autofocuses and can detect a single photon, skin studded with sensors for touch, heat, and pain, and a sense of smell that can detect chemicals down to the parts per trillion range. Our sense of hearing is pretty powerful, too, allowing us to not only hear sounds over a 140 dB range, but also to locate its source with a fair degree of precision, thanks to the pair of ears on our heads.

Recreating that binaural audio capture ability is the idea behind this homebrew 3D microphone. Commercially available dummy head microphones are firmly out of the price range of [LeoMakes] and most mortals, so his was built on a budget from a foam mannequin head and precast silicone rubber ears, which you can buy off the shelf, because of course you can.

Attached to the sides of the foam head once it got the [Van Gogh] treatment, the ears funnel sound to tiny electret cartridge microphones. [Leo] learned the hard way that these little capsule mics can’t use the 48-volt phantom power that’s traditionally pumped up the cable to studio microphones; he fixed that problem with a resistor in parallel with the mic leads. A filtering capacitor, an RC network between the cold line and ground on the balanced audio line, and a shield cleverly fashioned from desoldering braid took care of the RF noise problem.

The video after the break shows the build and test results, which are pretty convincing with headphones on. If you want to build your own but need to learn more about balanced audio and phantom power, we’ve got a short primer on the topic that might help.

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Drumming A Beat On A Hundred-Year-Old Typewriter

May 7, 2020 by Moritz v. Sivers 8 Comments

We have seen a fair share of unusual items being turned into musical instruments. Luckily, with a little bit of hacking it is possible to turn almost anything into a MIDI controller. [William Sun Petrus] just converted a 1920s typewriter into a drum machine and delivers a hell of a live performance on it.

The build is rather simple, all [William Sun Petrus] needed was an Arduino Mega and lots of wires to convert a hundred-year-old Remington typewriter into a MIDI controller. Whenever a key is pressed the hammer hits a metal plate at the center of the typewriter and closes the contact between one of the Arduino’s IO pins and the 5 V rail like a regular push button. The Arduino code is based on the MIDI library sending commands to a PC which is running Hairless MIDI and Ableton. As sort of a gimmick, [William Sun Petrus] included an LCD screen which shows a line from Green Eggs and Ham by Dr. Seuss every time a key is pressed.

Interestingly, the latency due to the hammer’s travel time does not disturb [William Sun Petrus’] live play. To calm the skeptics in the comments he also released an unedited version of the video to prove that the performance is real and an instructional video on how to play his beat note by note.

Other unusual MIDI controllers include a bandoneon accordion or this English concertina.

Video after the break.

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Ultrasonic Sound Gun Precisely Aims Your Music

April 30, 2020 by Moritz v. Sivers 25 Comments

When listening to music you sometimes cannot avoid the situation where other people get annoyed because they feel it disrupts their important doings or they do not share your taste in avant-garde doom metal. Of course one could just use headphones. But a hackier way would be to build a parametric speaker that focuses soundwaves into a narrow beam like [Shane] did with this ultrasonic sound gun.

As the directivity of a soundwave depends on the size of the source and its frequency, a directed beam can practically only be achieved with ultrasound. Even though we are not able to perceive frequencies above ~20 kHz, the nonlinear properties of air make it possible to hear the audio modulated onto an ultrasonic carrier signal. For his sound gun [Shane] was inspired by another parametric speaker project. It took him some time to get the 555 timer circuit oscillating at the right frequency and he fried a cheap Bluetooth audio module while trying to increase the output volume but in the end, he managed to get everything working. As the project name suggests, he also 3D printed a gun-shaped enclosure. The video below shows that the sound from the gun behaves really similar to a beam of light and can, for example, be bounced off other objects.

If you are looking for other inspiration there is a whole list of cool ultrasonic projects from distance sensors to acoustic levitation.

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Queue Up Your Tracks With A Well Placed Hexagon

April 24, 2020 by Tom Nardi 11 Comments

Besides a few stalwart holdouts, most of us have have switched over listening to music in digital form, often via an online stream. As long as no data caps stand in your way, it’s a quick and easy way to listen to your favorite artists or discover new ones. But there’s something visceral about act of loading a piece of physical media into a player that can’t be replicated by just clicking or tapping on a screen.

Which is why [InfiniteVideo] put together this RFID playlist launcher peripheral. There’s an important distinction to be made here, as this device isn’t actually playing or even storing audio. A nearby Raspberry running Volumio handles the actual playback. This device is just an RFID reader with some clever tokens that the listener can use to select their favorite artists and albums with physical tokens. It’s certainly not a new concept, but we think the nuances of this particular build warrant a closer look.

The “player” consists of a ESP8266 with a MFRC522 RFID reader wired directly to the GPIO pins. The pair are housed in a rather large 3D printed enclosure, which at first might seem a bit excessive. But it turns out that [InfiniteVideo] is actually trying to replicate a crowd sourced project called Qleek which is based around a similarly chunky reader.

Likewise, the hexagon tiles are also lifted from the Qleek concept. But rather than being made out of wood as in the original, [InfiniteVideo] is printing those as well. Halfway during the process, the print is paused and an RFID sticker is placed in the middle of the hexagon. Once resumed, the RFID tag becomes permanently embedded in the tile with no visible seams to reveal how the trick was pulled off. With the addition of a suitable label, each printed hexagon gets associated with the desired album or artist in software.

This project is notable for its convenience and visual flair, but using RFID tags for media identification can also be a practical choice. It can be used as an assistive technology, or as a way for young children to easily interact with devices.