ADSL Router As Effects Pedal

Moore’s law might not be as immutable as we once though thought it was, as chip makers struggle to fit more and more transistors on a given area of silicon. But over the past few decades it’s been surprisingly consistent, with a lot of knock-on effects. As computers get faster, everything else related to them gets faster as well, and the junk drawer tends to fill quickly with various computer peripherals and parts that might be working fine, but just can’t keep up the pace. [Bonsembiante] had an old ADSL router that was well obsolete as a result of these changing times, but instead of tossing it, he turned it into a guitar effects pedal.

The principle behind this build is that the router is essentially a Linux machine, complete with ALSA support. Of course this means flashing a custom firmware which is not the most straightforward task, but once the sound support was added to the device, it was able to interface with a USB sound card. An additional C++ program was created which handles the actual audio received from the guitar and sound card. For this demo, [Bonsembiante] programmed a ring buffer and feeds it back into the output to achieve an echo effect, but presumably any effect or a number of effects could be programmed.

For anyone looking for the source code for the signal processing that the router is now performing, it is listed on a separate GitHub page. If you don’t have this specific model of router laying around in your parts bin, though, there are much more readily-available Linux machines that can get this job done instead.

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Solar Cells As Art Form

When most of us approach a project, we have a certain problem to solve. 3D printing, microcontrollers, batteries, and all kinds of technologies are usually tools to accomplish some task. This is not necessarily true in the art world, though, where the intrinsic nature of these tools can be explored for their own sake rather than as a means to an end. The latest one that came across our desk is this light-powered sound generator.

The art piece looks a bit like a mobile with rotating arms, holding various small solar cells each connected to a speaker. As the arms pivot, the light falling on the cells changes which drives a specially-designed circuit connected to a speaker. The circuit acts as an oscillator, passing the changing voltage from the cell through various capacitors and transistors to produce changing tones in the speaker.

The effect of the rotating solar panels is not only oscillations from the speakers as the light changes, but oscillations in the sound of the speakers as they rotate towards and away from the observer. It’s a unique project and perfect for the art show it was in. It’s also not the only sound-focused art installation we’ve ever seen before, be sure to check out this one based on an ESP32.

Vintage Pro Audio Hack Chat Gets In The Groove

Despite the fact that we’ve been doing them for years now, it’s still hard to predict how a Hack Chat will go. There’s no question it will be an hour of interesting discussion of course, that much is a given. But the dynamics of the conversation can range from a rigid Q&A, which isn’t exactly unexpected when you’ve only got a limited amount of time with a subject matter expert, to a freewheeling hangout with a group of people who all happen to be interested in the same thing.

This week’s Vintage Pro Audio Hack Chat with Frank Olson definitely took the latter approach. The allotted hour flew by in a blink, with so many anecdotes and ideas flying back and forth that at times it was tricky to follow. But no worries, with the Chat transcript to pore over, we can make sure none of that accrued first-hand knowledge goes to waste.

So what did we learn during this Chat? Well, it probably won’t come as much of a surprise to find that those who have an opinion on audio gear tend to have a strong opinion on it. Folks were painting with some fairly broad brushes, with particular manufacturers and even whole fields of technology receiving a bit of good-natured ribbing. If your favorite brand or piece of gear gets a specific shout-out, try not to take it too personally — at the end of the day, most in the Chat seemed to agree that sound is so subjective that the right choice is more often than not whatever sounds best to you at the moment.

Which leads directly into Frank’s work with custom microphones. As a musician he knew the sound he was looking for better than anyone, so rather than spend the money on big-name gear, he prefers to build it himself. But the real hook here is their unique construction, with pieces that reimagine design concepts from mid-century commercial equipment using unexpected materials such as thin pieces of walnut cut with a vinyl cutter. Frank explains that the structure of the microphone isn’t as critical these days thanks to the availability of powerful neodymium magnets, which gives the builder more freedom in terms of materials and tools. He says the goal is to inspire others to try building gear from what’s available to them rather than assuming it won’t work because it’s unconventional.

We appreciate Frank, and everyone else, stopping by this week for such a lively and friendly discussion. Let’s be honest, a Chat specifically for folks who want to discuss concepts as personal and nebulous as how they perceive the warmth of sound could have gotten a little heated. But the fact that everyone was able to express their opinions or ask for advice constructively is a real credit to the community.

The Hack Chat is a weekly online chat session hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers connect in a fun and informal way, but if you can’t make it live, these overview posts as well as the transcripts posted to make sure you don’t miss out.

How Did Dolby Digital Sound Work On Film?

When we go to the cinema and see a film in 2022, it’s very unlikely that what we’re seeing will in fact be a film. Instead of large reels of transparent film fed through a projector, we’ll be watching the output of a high-quality digital projector. The advantages for the cinema industry in terms of easier distribution and consistent quality are obvious. There was a period in the 1990s though when theatres still had film projectors, but digital technology was starting to edge in for the sound. [Nava Whiteford] has found some 35mm trailer film from the 1990s, and analysed the Dolby Digital sound information from it.

The film is an interesting exercise in backward compatibility, with every part of it outside the picture used to encode information. There is the analogue sound track and two digital formats, but what we’re interested in are the Dolby Digital packets. These are encoded as patterns superficially similar to a QR code in the space between the sprocket holes.

Looking at the patent he found that they were using Reed-Solomon error correction, making it relatively easy to decode. The patent makes for fascinating reading, as it details how the data was read using early-1990s technology with each line being scanned by a linear CCD, before detailing the signal processing steps followed to retrieve the audio data. If you remember your first experience of Dolby cinema sound three decades ago, now you know how the system worked.

The film featured also had an analogue soundtrack, and if you’d like to know how they worked, we’ve got you covered!

Speed of motion test setup

Simple Setup Answers Complex Question On The Physics Of Solids

Thought experiments can be extremely powerful; after all, pretty much everything that [Einstein] came up with was based on thought experiments. But when a thought experiment turns into a real experiment, that’s when things can get really interesting, and where unexpected insights crop up.

Take [AlphaPhoenix]’s simple question: “Are solid objects really solid?” On the face of it, this seems like a silly and trivial question, but the thought experiment he presents reveals more. He posits that pushing on one end of a solid metal rod a meter or so in length will result in motion at the other end of the rod pretty much instantly. But what if we scale that rod up considerably — say, to one light-second in length. Is a displacement at one end of the rob instantly apparent at the other end? It’s a bit of a mind-boggler.

To answer the question, [AlphaPhoneix] set up a simple experiment with the aforementioned steel rod — the shorter one, of course. The test setup was pretty clever: a piezoelectric sensor at one end of the bar, and a hammer wired to a battery at the other end, to sense when the hammer made contact with the bar. Both sensors were connected to an oscilloscope to set up to capture the pulses and measure the time. It turned out that the test setup was quite a challenge to get right, and troubleshooting the rig took him down a rabbit hole that was just as interesting as answering the original question. We won’t spoil the ending, but suffice it to say we were pleased that our first instinct turned out to be correct, even if for the wrong reasons.

If you haven’t checked out [AlphaPhoenix] yet, you really should. With a doctorate in material science, he’s got an interesting outlook on things, like calculating pi using raindrops or keeping the “ultra” in ultra-high vacuum. Continue reading “Simple Setup Answers Complex Question On The Physics Of Solids”

Ray's panels on the wall - circles of different sizes (from 60 to 15cm in diameter) covered by fabric of different shades, their arrangement vaguely resembling a cloud.

DIY Acoustic Panels Or Modern Artwork? Can’t Tell

The acoustic properties of a room have a surprising impact when you want to use a microphone. [RayP24]’s son was trying to make his bedroom into a better recording studio, and for [Ray], that turned into an artfully-executed wall panel project. Fortunately, the process is documented so we all can learn from it. When it comes to acoustics, you can often get a whole lot of improvement from surprisingly few changes. And, as this project demonstrates, you can make it look like a decorative piece to boot.

When arranged and placed on the wall, these panels look like an art piece, a decoration you could get from a somewhat fancy store. If you show them to someone, they might not believe that they also serve as a functioning home acoustics improvement, dampening the sound quite well for audio recording needs. The panels are built out of individual circles, cut out in a way that uses as much of a 3/16″ (5mm) plywood sheet as possible, with hollow circles serving as frames to attach foam-backed fabric. In the Instructables post, [Ray] talks quite a bit about how you can assemble your own and what liberties you can take. There’s also a short video accompanying this project, which you can see after the break. This project is begging to be recreated.

There’s a sizeable amount of hacking-meets-home improvement-meets-home acoustics projects out there, especially lately, when so many people are stuck at home for one reason or another. Just a few months ago, we covered another marvelous “art piece turned reverb killer” project operating by a slightly different principle, and also going a bit more into the theory. Perhaps in a few years, we will no longer have to build panels or structures for our soundproofing needs, as purpose-grown mycelium shapes will do that for us. And once it becomes a question of where to hang your newly-built acoustic panels, this simple guide is a good place to start.

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When A Single Bit Was Enough, Into The Sound Of The ZX Spectrum

It’s normal for a computer in 2022 to come with a fully-featured sound card containing a complete synthesizer as well as high-quality PCM sound recording and playback. It’s referred to as a sound card after the way the hardware first appeared in the world of PCs, but in fact it’s now considered so essential as to be a built-in part of most mainboards. There was a time when computers boasted considerably less impressive sound hardware, and among the chorus of SIDs and AY chips of the perhaps the least well-featured was the original Sinclair ZX Spectrum. Its one-bit sound, a single line on an I/O port, is the subject of a thorough investigation from [Forgotten Computer]. It’s a long video which we’ve placed below the break, but for those with an interest in 8-bit music it should make a for a fascinating watch.

For Sir Clive Sinclair the 1-bit audio must have been welcome as it removed the need for an expensive sound chip and kept the Spectrum to its low price point, but on the face of it there was little more it could do than create simple beeps using Sinclair BASIC’s built-in BEEP command. The video gives us an in-depth look at how interleaving and PWM could be used to create much more complex sounds such as the illusion of multiple voices and even sampled sounds. In particular his technique of comparing the audio output with its corresponding pin on the Sinclair ULA shows the effect of the machine’s simple low-pass filter, though the music was often so close to the edge of what the interface could do that aliasing sounds are often very obvious.

As he demonstrates the various ingenious techniques that game and demo developers used to extract performance from such limited hardware that could even try to compete with the more sophisticated machines even at the same time as their code was running whatever was on the screen, it’s difficult not to come away with immense respect for their skills. If you’ve ever experimented with computer audio then you should try hardware this simple for yourself.

Continue reading “When A Single Bit Was Enough, Into The Sound Of The ZX Spectrum”