Walkmp3rson Is An MP3 Player Like Sony Never Made

September 20, 2022 by Kristina Panos 29 Comments

If you weren’t already well aware, the 90s are like, so hot right now, and that includes cassette tapes for some reason. (Even though we personally didn’t have a CD player until 1998, they were around as early as 1982.) But if you don’t dig the quality of cassettes, or if you’d just rather carry around more than 45-120 minutes worth of music, than [John Edgar Park]’s Walkmp3rson is definitely the build for you. That’s pronounced ‘Walkperson’, as in a 21st century MP3-based update of the classic Walkman.

Inside this amazing 3D printed enclosure, you’ll find an Adafruit Feather RP2040 controlling the screen, handling input from the rotary encoder and those sweet mechanical keyswitches, and of course, playing audio files from SD cards through the amplifier breakout board. And no, this isn’t just another MP3 player — well, it kind of is, but the presentation really goes a long way here.

There are tons of retro-modern nods, like the cassette reel animation that plays on the TFT screen, the boxy enclosure, and the fact it involves physical media. Oh yes — you get to insert an SD card whenever you want to change albums/discographies/genres/whatever. In fact, this would be a great use of older, smaller SD cards. You could go all out and make tiny album art to slip inside those milky plastic cases. Check out the brief demo video after the break.

Looking to play your tunes on a microcontroller, but not a fan of the Walkman aesthetic? In June we covered a similar audio player powered by the ESP32 that does an uncanny impersonation of a portable tape deck that you might be interested in.

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How The BBC (Still) Sends Audio To Transmitter Sites

September 13, 2022 by Jenny List 25 Comments

Running a radio station is, on the face of it, a straightforward technical challenge. Build a studio, hook it up to a transmitter, and you’re good to go. But what happens when your station is not a single Rebel Radio-style hilltop installation, but a national chain of transmitter sites fed from a variety of city-based studios? This is the problem facing the BBC with their national UK FM transmitter chain, and since the 1980s it has been fed by a series of NICAM digital data streams. We mentioned back in 2016 how the ageing equipment had been replaced with a modern FPGA-based implementation without any listeners noticing, and now thanks to [Matt Millman], we have a chance to see a teardown of the original 1980s units. The tech is relatively easy to understand from a 2020s perspective, but it still contains a few surprises.

In each studio or transmitter site would have been a 19″ rack containing one of these units — a card frame with a collection of encoder or decoder cards. These are all custom-made by the BBC’s engineering department to a very high standard, and use period parts such as the familiar Z80 microprocessor and some Philips digital audio chips, which followers of high-end consumer audio may recognize. As you’d expect for a mission critical device, many of the functions are duplicated for redundancy, with their outputs compared to give warning of failures.

The surprise comes in the NICAM encoder and decoder — it’s a custom LSI chip made exclusively for the BBC. This indicates the budget available to the national broadcaster, and given that these units have in some cases been working for over 35 years, we’re guessing that the license payers got their money’s worth.

You can read about the original switch-over in 2016, and a little more about NICAM, too.

Get Your Raspberry Pi Jamming With MuPiBox

August 15, 2022 by Tom Nardi 7 Comments

Over the years we’ve seen a lot of Raspberry Pi boards pushed into service as media players. In fact, second to emulating old game consoles, that’s probably the Pi’s most common vocation when it comes to DIY builds. But despite the popularity of this particular use case, it seems like each one has had to reinvent the wheel.

Perhaps there’s where MuPiBox fits in. Developed by [Eric Gerhardt] and [Olaf Split] with the assistance of [Andreas Lippmann] and [Andrew Frericks], this project aims to turn everyone’s favorite Linux single-board computer into everyone’s favorite music player. MuPiBox provides not only the software to run your new high-tech boom box, but it even standardizes the hardware design and provides a 3D printable enclosure — though naturally there’s still room for interpretation if you don’t want yours to look exactly like all the others.

Your MuPiBox can look like whatever you want.

At the very minimum you’ll need a Raspberry Pi, a HifiBerry MiniAmp, and a speaker, though the instructions also recommend you invest in a Pimoroni OnOff SHIM (or wire up something comparable) to facilitate more graceful shutdowns. For the best experience you’ll also want a five inch Waveshare touch screen display and a USB power bank so your beats can go mobile.

The video below shows off the polished stock GUI, which is simple enough that even children should be able to navigate around and find their favorite tracks. Which is good, especially since it’s in German. The video also shows off some advanced setup features so you don’t have to pull the SD card out of the Pi just to change the WiFi network it’s attached to. There’s also a web interface that you can access from other devices on the network.

It’s a slick project, and we really like the aesthetics of the 3D printable enclosure. But even if you don’t want to replicate the project exactly, there’s certainly components here which could be utilized in your own Pi media center build.

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Remove A Speaker’s Voice From A Recording Using Ultrasound

August 12, 2022 by Maya Posch 15 Comments

What if you could effectively prevent someone from recording your voice? This is the focus of a study by Guo et al. (2022) at Michigan State University, in which they use a dynamically calculated audio signal that effectively cancels out one’s voice in a recording device. This relies on an interesting aspect of certain micro-electro-mechanical system (MEMS) microphones, which are commonly used in smartphones and other recording devices.

Pressure sensitivity of a MEMS microphone. (credit: Brian R. Elbing)

A specially crafted ultrasound signal sent to the same microphone which is recording one’s voice can result in the voice audio signal being gone on the final recording. The approach taken by the authors involves using a neural network that is trained on voice samples of the person (“Bob”) whose voice has to be cancelled. After recording Bob’s voice during a conversation, the creatively named Neurally Enhanced Cancellation (NEC) system determines the ultrasound signal to be sent to the target recording device. Meanwhile the person holding the recording device (“Alice”) will still perceive Bob’s voice normally.

As ultrasound is highly directional, the system can only jam a specific microphone and wouldn’t affect hidden microphones in a room. As noted by the authors, it is possible to do general microphone jamming using other systems, but this is legally problematic, which should not be an issue with their NEC system.

Thanks to [JohnU] for the tip!

Build Your Own 3D Printed Bluetooth Headphones

August 5, 2022 by Tom Nardi 20 Comments

A few years back, [Shannon Ley] wondered how hard it would be to build a pair of Bluetooth headphones from scratch. Today, we have our answer. The Homebrew Headphones website is devoted to just one thing: explaining how you can use common components and some 3D printed parts to build an impressively comprehensive pair of wireless headphones for around $50 USD.

The headphones pair a CSR8645 Bluetooth audio receiver with a TP4056 USB-C charging module, a 500 mAh LiPo pouch battery, a pair of Dayton Audio CE38MB-32 drivers, and replacement ear covers designed for the Bose QuietComfort QC15. Some perfboard, a couple buttons, a resistor, and an LED round out the parts list.

All of the components fit nicely into the meticulously designed 3D printed frame, and assembly is made as simple as possible thanks to an excellent step-by-step guide. It’s all so well documented that anyone with even basic soldering experience should be able to piece it together without too much fuss.

Of course, these aren’t the first 3D printed headphones we’ve ever seen. But the quality of the documentation and attention to detail really make these stand out.

An Affordable Reference Mic You Can Build Yourself

July 2, 2022 by Lewin Day 12 Comments

Reference mics are vital tools for audio work. They’re prized for their flat frequency response, and are often used for characterizing the audio response of a room or space. OpenRefMic aims to be an open source design for producing reference mics without paying exorbitant retail prices.

The heart of the build is a preamplifier that runs off standard 48 V phantom power, and is responsible for both biasing the electret microphone element and acting as a buffer for the mic signal. It’s designed specifically to work with the PUI AOM-5024L-HD-F-R mic capsule, chosen for its good performance and low noise characteristics. However, other electric mics should work, too. The hardware is wrapped up in a 3D printed case which can readily be made on most basic printers. It’s complete with a press-fit grille that holds the mic capsule in place.

The prime goal of the project is low noise; the project creator, [loudifier], notes that most commercial reference mics focus first on flat frequency response and then reducing noise. OpenRefMic performs well in this area, and its lack of a perfectly flat frequency response is countered with calibrated equalization. It also works with regular pro-grade XLR cables and phantom power, rather than needing fancy laboratory-spec cables and interfaces.

The final result is a credit to [loudifier], who demonstrates a strong understanding of the principles of reference mic design. We’ve seen some other great low-cost reference mics recently, too!

Unraveling The Hackaday Podcast Hidden Message

July 1, 2022 by Tom Nardi 7 Comments

When Elliot and I record the raw audio for the weekly podcast, it’s not unusual for us to spend the better part of two hours meandering from topic to topic. During one of these extended gab sessions, we wondered if it would be possible to embed a digital signal into the podcast in such a way that it could be decoded by the listener. Of course, storing and transmitting data via sound is nothing new — but the podcast format itself introduced some level of uncertainty.

Would the encoded sound survive the compression into MP3? Would the syndication service that distributes the file, or the various clients listeners will use to play it back, muddy the waters even further? Was it possible that the whole episode would get flagged somewhere along the line as malicious? After a bit of wild speculation, the conversation moved on to some other topic, and the idea was left to stew on one of our infinite number of back burners.

That is, until Elliot went on vacation a couple weeks back. In place of a regular episode, we agreed that I’d try my hand at putting together a special edition that consisted of pre-recorded segments from several of the Hackaday contributors. We reasoned this simplified approach would make it easier for me to edit, or to look at it another way, harder for me to screw up. For the first time, this gave me the chance to personally oversee the recording, production, and distribution of an episode. That, and the fact that my boss was out of town, made it the perfect opportunity to try and craft a hidden message for the Hackaday community to discover.

I’m now happy to announce that, eleven days after the EMF Camp Special Edition episode was released, ferryman became the first to figure out all the steps and get to the final message. As you read this, a coveted Hackaday Podcast t-shirt is already being dispatched to their location.

As there’s no longer any competition to see who gets there first, I thought it would be a good time to go over how the message was prepared, and document some interesting observations I made during the experiment.

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