Day: June 5, 2020

Turning A MicroKORG Into A MicroKORG S With This Speaker Mod

June 5, 2020 by 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.

Continue reading “Turning A MicroKORG Into A MicroKORG S With This Speaker Mod” →

This Week In Security: Exim, Apple Sign-in, Cursed Wallpaper, And Nuclear Secrets

June 5, 2020 by 9 Comments

So first off, remember the Unc0ver vulnerability/jailbreak from last week? In the 13.5.1 iOS release, the underlying flaw was fixed, closing the jailbreak. If you intend to jailbreak your iOS device, make sure not to install this update. That said, the normal warning applies: Be very careful about running out-of-date software.

Apple Sign In

An exploit in Apple’s web authentication protocol was fixed in the past week . Sign In With Apple is similar to OAuth, and allows using an Apple account to sign in to other sites and services. Under the hood, a JSON Web Token (JWT) gets generated and passed around, in order to confirm the user’s identity. In theory, this scheme even allows authentication without disclosing the user’s email address.

So what could go wrong? Apparently a simple request for a JWT that’s signed with Apple’s public key will automatically be approved. Yeah, it was that bad. Any account linked to an Apple ID could be trivially compromised. It was fixed this past week, after being found and reported by [Bhavuk Jain]. Continue reading “This Week In Security: Exim, Apple Sign-in, Cursed Wallpaper, And Nuclear Secrets” →

Tic-Tac-Toe Implemented In Single Call To Printf()

June 5, 2020 by 34 Comments

[Nicholas Carlini] programmed a C implementation of two-player Tic Tac Toe, and he did it in a single call to printf(). The arguments for that single function call get mind-bendingly complex, so it may come as no surprise that it was written for The International Obfuscated C Code Contest (IOCCC).

Most of us are aware that printf() is one of those functions that is considerably more complex under the hood, and capable of far more, than it may appear to be. But did you know that it is capable of Turing-complete computation?

[Nicholas] clearly steps through the theory, so give it a read. In short, a maze of arguments handles the logic of the game while an embedded scanf() reads user input, and printing the game board is always preceded by an escape code to clear the screen.

[Nicholas] is certainly no stranger to in-depth understandings; we’ve seen his work before in demonstrating how to fool speech recognition with hidden commands, including a powerful example showing how two virtually identical-sounding audio files transcribe entirely differently.

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

June 5, 2020 by 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.