It’s An Audio Distortion Analyzer, Just Not The One You Were Hoping For

December 19, 2023 by Jenny List 7 Comments

An audio distortion analyzer is a specialist piece of analogue test equipment that usually costs a lot of money and can be hard to track down on the second hand market. Finding one is a moment of luck for the average engineer then, but [Thomas Scherrer OZ2CPU]’s discovery isn’t quite what he might have hoped for. Nonetheless, his Bang and Olufsen K3 Distortion meter DM1 from 1979 is still an interesting and high quality piece of test equipment, and the video below the break makes for a worthwhile watch.

Bang and Olufsen are best known for high-end design Hi-Fi units, thus it’s a surprise to find that in the past they also manufactured test equipment. This distortion meter isn’t a general purpose one, instead it’s designed to measure tape recorders in particular, and it uses an elegant technique. Instead of injecting a sine wave and removing it from what comes out in order to measure the products of the distortion, it records a 333 Hz sine wave onto a tape, then measures the strength of its 3rd harmonic at 1 kHz as an indication of distortion. It’s a working distortion meter made with clever analogue circuitry for a fraction of the cost of the more conventional models that HP would have sold you at the same time, even if it doesn’t give the same THD figure you might have been looking for.

If distortion interests you, it’s a subject we’ve looked at in the past.

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Keeping A Mazda’s Radio On After The Engine Shuts Off

November 22, 2023 by Lewin Day 51 Comments

Have you ever pulled into a car park with your favorite song blaring, only to lament the fact that the music cut out when you stopped the engine? Some modern cars are smart enough to keep the radio on until you open the door. [ssh16] decided to hack that very functionality into their Mazda MX-5.

The device uses a microcontroller to read the CAN bus of the vehicle. The microcontroller also has the ability to keep the vehicle’s ACC (accessory) relay energized at will. Thus, when the engine is turned off, the microcontroller keeps the ACC relay on, maintaining power to the stereo and infotainment system. Then, after ten minutes, or when it receives a CAN message that the driver’s door has been opened, it cuts power to the relay, shutting the accessories off. It’s a simple build, but one that [ssh16] executed cleanly. By putting the microcontroller on a neat PCB with a harness that can clip into the stock Mazda one, it’s possible to install the hack without needing to cut any wires. Plus, with a small modification, it was even possible to use the same hack with a Mazda CX-5.

Whether you’re jamming out to a cool song, or you just want to finish a phone call over Bluetooth, it’s a nifty feature to have in a vehicle. We’ve seen some other neat infotainment hacks before, too. Video after the break.

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Stream Vinyl To Your Sonos Without The Financial Penalty

November 13, 2023 by Jenny List 47 Comments

One of the unexpected success stories in the world of hi-fi over the past decade has been the resurgence of the vinyl LP as a musical format. What was once old hat is now cool again, but for freshy minted vinyl fans there’s a snag. Hi-fi itself has moved on from the analogue into the digital, so what can be done if your listening comes through a Sonos system. Sonos will sell you a box to do that of course, but it’s as overpriced as 2023-pressing vinyl. [Max Fischer] has a far better solution, in the form of a Raspberry Pi loaded with open source software.

At the vinyl end is a Behringer audio interface containing a pre-amp with the required RIAA response curve. This acts as the source for the DarkIce audio streamer and the IceCast2 media serer, all of which even with the cost of a Pi and the interface, is considerably less than the commercial device.

We’re guessing that a more humble interface coupled to an older RIAA pre-amp could cut the cost further, and we’d be hugely curious as to whether a simple mic pre-amp could be used alongside some DSP from the likes of Gnu Radio to give the RIAA response.

Either way, he’s made a handy device for any 21st-century vinyl fan. Meanwhile if you’re one of the streaming generation seduced by round plastic discs, we’ve gone into some detail about their audiophile credentials in the past. And if you have found yourself a turntable, of course you’ll need to know how to set it up properly.

Open Source Ear Monitoring Platform Listens To Your Ears

October 17, 2023 by Richard Baguley 17 Comments

All sorts of exciting things happen in your ears, and now there is a good open source way to monitor them. Open Earable is a new project from a group of researchers and companies that monitors and records what is going on in your ear.

The project is designed as an easy-to-build, cheap way for audiologists and others to capture data about what is happening inside and around the ear. It’s a clip-on device that looks like a small hearing aid but has a six-degree Inertial Measurement Unit (IMU) and several other sensors to measure things around your ear and inside the ear canal. A pressure and temperature sensor measures the air pressure and temperature just inside the ear canal, and a small speaker can squirt sound right in there.

A button on the outside allows the user to control the device, and it can play back or record sound to the internal SD card memory. These are all controlled by an Arduino that includes Bluetooth Low Energy. The existing design only allows you to play a stored WAV file, not streaming audio. That’s a solvable problem, though, so it could also be turned into a set of hacker headphones.

Joking aside, this looks like an exciting research project and a useful tool for researchers. The GitHub repository for version 1.3 of the project lays it all out, including a full BoM and code, and the STL files for the case and PCB designs are in the Resources section of the site.

[Updated 18/10/2023 to correct IMU to Measurement, not Management. Intertial management needs a different set of devices]

Sine-wave Speech Demonstrates An Auditory One-way Door

October 7, 2023 by Donald Papp 41 Comments

Sine-wave speech can be thought of as a sort of auditory illusion, a sensory edge case in which one’s experience has a clear “before” and “after” moment, like going through a one-way door.

Sine-wave speech (SWS) is intentionally-degraded audio. Here are the samples, and here’s what to do:

Choose a sample and listen to the sine-wave speech version (SWS). Most people will perceive an unintelligible mix of tones and beeps.
Listen to the original version of the sentence.
Now listen to the SWS version again.

Most people will hear only some tones and beeps when first listening to sine-wave speech. But after hearing the original version once, the SWS version suddenly becomes intelligible (albeit degraded-sounding).

These samples were originally part of research by [Chris Darwin] into speech perception, but the curious way in which one’s experience of a SWS sample can change is pretty interesting. The idea is that upon listening to the original sample, the brain — fantastic prediction and learning engine that it is — now knows better what to expect, and applies that without the listener being consciously aware. In fact, if one listens to enough different SWS samples, one begins to gain the ability to understand the SWS versions without having to be exposed to the originals. In his recent book The Experience Machine: How Our Minds Predict and Shape Reality, Andy Clark discusses how this process may be similar to how humans gain fluency in a new language, perceiving things like pauses and breaks and word forms that are unintelligible to a novice.

This is in some ways similar to the “Green Needle / Brainstorm” phenomenon, in which a viewer hears a voice saying either “green needle” or “brainstorm” depending on which word they are primed to hear. We’ve also previously seen other auditory strangeness in which the brain perceives ever-increasing tempo in music that isn’t actually there (the Accelerando Illusion, about halfway down the list in this post.)

Curious about the technical details behind sine-wave speech, and how it was generated? We sure hope so, because we can point you to details on SWS as well as to the (free) Praat software that [Chris] used to generate his samples, and the Praat script he wrote to actually create them.

Just What Is Tone, In A Microphone?

October 5, 2023 by Jenny List 23 Comments

As long-time Hackaday readers will know, there is much rubbish spouted in the world of audio about perceived tone and performance of different hi-fi components. Usually this comes from audiophiles with, we’d dare to suggest, more money than sense. But oddly there’s an arena in which the elusive tone has less of the rubbish about it and it in fact, quite important. [Jim Lill] is a musician, and like all musicians he knows that different combinations of microphones impart a different sound to the recording. But as it’s such a difficult property to quantify, he’s set out to learn all he can about where the tone comes from in a microphone.

He’s coming to this from the viewpoint of a musician rather than an engineer, but his methodology is not diminished by this. He’s putting each mic on test in front of the same speaker at the same position, and playing a standard piece of music and a tone sweep through each. He doesn’t have an audio analyser, reference speaker and microphone, or anechoic chamber, so he’s come up with a real-world standard instead. He’s comparing every mic he can find with a Shure SM57, the go-to general purpose standard in the world of microphones for as long as anyone can remember, being a 1960s development of their earlier Unidyne series. His reasoning is that while its response is not flat the sound of the SM57 is what most people are used to hearing from a microphone, so it makes sense to measure the others against its performance.

Along the way he tests a huge number of microphones including famous and expensive ones from exclusive studios and finally one he made himself by mounting a cartridge atop a soda can. You’ll have to watch the video below the break for his conclusions, we can promise it’s worth it.

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Robotic Mic Swarm Helps Pull Voices Out Of Crowded Room Of Multiple Speakers

October 4, 2023 by Lewin Day 27 Comments

One of the persistent challenges in audio technology has been distinguishing individual voices in a room full of chatter. In virtual meeting settings, the moderator can simply hit the mute button to focus on a single speaker. When there’s multiple people making noise in the same room, though, there’s no easy way to isolate a desired voice from the rest. But what if we ‘mute’ out these other boisterous talkers with technology?

Enter the University of Washington’s research team, who have developed a groundbreaking method to address this very challenge. Their innovation? A smart speaker equipped with self-deploying microphones that can zone in on individual speech patterns and locations, thanks to some clever algorithms.

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