How To Build Jenny’s Budget Mixing Desk

February 15, 2023 by Jonathan Bennett 35 Comments

Jenny did an Ask Hackaday article earlier this month, all about the quest for a cheap computer-based audio mixer. The first attempt didn’t go so well, with a problem that many of us are familiar with: Linux applications really doesn’t like using multiple audio devices at the same time. Jenny ran into this issue, and didn’t come across a way to merge the soundcards in a single application.

I’ve fought this problem for a while, probably 10 years now. My first collision with this was an attempt to record a piano with three mics, using a couple different USB pre-amps. And of course, just like Jenny, I was quickly frustrated by the problem that my recording software would only see one interface at a time. The easy solution is to buy an interface with more channels. The Tascam US-4x4HR is a great four channel input/output audio interface, and the Behringer U-PHORIA line goes all the way up to eight mic pre-amps, expandable to 16 with a second DAC that can send audio over ADAT. But those are semi-pro interfaces, with price tags to match.

But what about Jenny’s idea, of cobbling multiple super cheap interfaces together? Well yes, that’s possible too. I’ll show you how, but first, let’s talk about how we’re going to control this software mixer monster. Yes, you can just use a mouse or keyboard, but the challenge was to build a mixing desk, and to me, that means physical faders and mute buttons. Now, there are pre-built solutions, with the Behringer X-touch being a popular solution. But again, we’re way above the price-point Jenny set for this problem. So, let’s do what we do best here at Hackaday, and build our own. Continue reading “How To Build Jenny’s Budget Mixing Desk” →

A closeup of a black flexible PCB with an out-of-focus quarter in the background, approximately the same size as the end of the PCB we're looking at. One the right is a USB C connector and to its left are two SMD components with visible pins. Several smaller SMD components (resistors or caps?) are soldered to other parts of the board.

Making The AirPods Pro Case Repairable

February 13, 2023 by Navarre Bartz 8 Comments

Apple is often lauded for its design chops, but function is often sacrificed at the altar of form, particularly when repair is involved. [Ken Pillonel] has made it easier for everyone to replace the batteries or lightning port in the AirPods Pro case. (YouTube)

With such notable hacks as adding USB C to the iPhone already under his belt, [Pillonel] has turned his attention to fixing the notoriously poor repairability of AirPods and AirPods Pro, starting with the cases. While the batteries for these devices are available, replacement Lightning ports are not, and taking the housing apart for the case is an exercise in patience where the results can’t be guaranteed.

He designed a USB C replacement port for broken Lightning ports that is a perfect fit if you happen to get the case apart in one piece. If you’re less successful, he has you covered there too with a 3D printable enclosure replacement.

We sure miss the days of schematic proliferation here at Hackaday, but we know you don’t let glued enclosures or unobtainium parts stand in the way of repairs.

Continue reading “Making The AirPods Pro Case Repairable” →

Count Leading Zeros For Efficient Logarithms

February 7, 2023 by Chris Lott 14 Comments

[Ihsan Kehribar] points out a clever trick you can use to quickly and efficiently compute the logarithm of a 32-bit integer. The technique relies on the CLZ instruction which counts the number of leading zeros in a machine word and is available in many modern processors. Typical algorithms used to compute logarithms are not quick and have a variable execution time depending on the input value. The technique [Ihsan] is using is both fast and has a constant run time.

The above equation summarized the math behind the algorithm. We get the first term easily using the CLZ instruction. Using the remainder and a pre-computed lookup table, it is possible to get the second term to various degrees of accuracy, depending on how big you make the table and whether or not you take the performance hit of interpolation or not — those of a certain age will no likely groan at the memory of doing interpolation by hand from logarithm tables in high school math class. [Ihsan] has posted an MIT-licensed implementation of this technique in his GitHub repository, which includes both the C-language algorithm and Python tools to generate the lookup table and evaluate the errors.

Why would you do this? Our first thought was real-time streaming DSP operations, where you want fast and deterministic calculations, and [Ihsan]’s specifically calls out embedded audio processing as one class of such applications. And he should know, after all, since he developed a MIDI capable polyphonic FM synthesizer on a Cortex M0 that we covered way back in 2015.

Ask Hackaday: The Ten Dollar Digital Mixing Desk?

February 6, 2023 by Jenny List 110 Comments

There comes a point in every engineer’s life at which they need a mixing desk, and for me that point is now. But the marketplace for a cheap small mixer just ain’t what it used to be. Where once there were bedroom musicians with a four-track cassette recorder if they were lucky, now everything’s on the computer. Lay down as many tracks as you like, edit and post-process them digitally without much need for a physical mixer, isn’t it great to be living in the future!

This means that those bedroom musicians no longer need cheap mixers, so the models I was looking for have disappeared. In their place are models aimed at podcasters and DJs. If I want a bunch of silly digital effects or a two-channel desk with a crossfader I can fill my boots, but for a conventional mixer I have to look somewhat upmarket. Around the three figure mark are several models, but I am both a cheapskate and an engineer. Surely I can come up with an alternative. Continue reading “Ask Hackaday: The Ten Dollar Digital Mixing Desk?” →

A MiniDisc Walkman, a MiniDisc and a pair of BlueTooth earphones

Wireless MiniDisc Walkman Has Bluetooth Inside

January 29, 2023 by Robin Kearey 17 Comments

For most people, MiniDisc is just one of countless media formats that became obsolete when music went online. Not so for MiniDisc enthusiasts, many of whom still use a MiniDisc deck at home and a MiniDisc Walkman on the go. Unfortunately, high-end headphones these days often come with Bluetooth connectivity only, necessitating the use of clunky signal converters that ruin the tidy compactness of those portable players. [Daniel Rojas] cleverly solved this problem by directly adding Bluetooth functionality to a Sony MZ-R500 MiniDisc Walkman.

MiniDisc Walkmen are famously compact devices, so adding a full circuit board to one wasn’t easy. [Daniel] managed to squeeze the PCB from a Schosche wireless audio transmitter inside the front of the Walkman, next to the control buttons. He connected the audio signal to the transmitter’s input and rewired the little-used “End Search” button to become the “Pair” button. Sadly, the recording head and some associated hardware had to be removed in order to make space for the new component, turning the Walkman into a playback-only device.

A MiniDisc Walkman, opened up and showing a BlueTooth module inside — Lots of flying wires and Kapton tape, but it all fits.

The project’s GitHub page contains a detailed walk-through of the modification process that should enable anyone to reproduce the end result. [Daniel] didn’t arrive at the optimal solution in one go however, and he describes the three major revisions of his project in separate sections. In the first iteration for example, the Bluetooth module caused interference on the audio signal, which [Daniel] solved by adding isolation transformers in version two. He also includes a page full of technical information he collected during his project, which will come in handy if you ever want to perform other modifications on your MiniDisc Walkman.

We’ve seen several impressive projects where Bluetooth interfaces were added to pre-Bluetooth gadgets, ranging from tube radios to 8-track players. Some, like the iPod Nano, are even more space-constrained than a MiniDisc Walkman. Continue reading “Wireless MiniDisc Walkman Has Bluetooth Inside” →

Reading Data From A CD, With A Microscope

January 22, 2023 by Jenny List 18 Comments

There was a time when electronic engineering students studied the audio CD, for all its real-world examples of error correction and control systems. There’s something to be found in the system still for young and old though, and thus we were intrigued when we saw [Peter Monta] reading the data from a CD using a microscope.

CDs encode data as so-called pits and lands in a spiral track across a metalised surface, with a transition from pit to land signifying a logic 1 and a missing transition signifying a 0. Reading a section of the raw data is achieved in the first part of his write-up, but in the next installment he goes further into retrieving more data through stitching together microscope pictures and writing some code to retrieve data frames. He’s not quite at the audio playback stage, but he’s planning in the future to spiral-track a full image to rip an entire disc.

There are plenty of CD drives around to read audio the conventional way, but the techniques here still find a use where less ubiquitous media has to be read. In the last decade for example there was an effort to read the BBC Domesday Project from the 1980s, as it became clear that few of the original readers survived in working order.

Dittytoy recreation of Jean-Michel Jarre's Oxygene Part IV

Generative Music Created In Minimalistic Javascript Code

January 2, 2023 by Joseph Long 10 Comments

Dittytoy user [srtuss] has recreated one of the most influential works of electronic music in an elegant nineteen kilobytes of Javascript code. The recreation of Jean-Michel Jarre’s Oxygene Part IV on the Dittytoy platform, currently in beta, plays live right in your browser. Dittytoy empowers users to create generative music online using a simple Javascript API. Syntax of the API is loosely based on that of Sonic Pi, a code-based music creation and performance tool.

“Oxygene (Part IV)” was recorded by Jean-Michel Jarre in 1976. It was Jarre’s most successful single, charted on the top ten in several countries, and was more recently featured in the Grand Theft Auto IV video game. In the 1990s, famed electronic music innovator Brian Eno used the term “generative music” to describe music generated by an electronic system comprising ever-changing elements that may be algorithmic or random.

Recreation of Jarre’s work required modeling the Korg Minipops 7 drum machine, one of the instruments presented in our slew of open-source synthesizers.