In previous episodes of this long-running series looking at the world of high-quality audio, at every point we’ve stayed in the real world of physical audio hardware. From the human ear to the loudspeaker, from the DAC to measuring distortion, this is all stuff that can happen on your bench or in your Hi-Fi rack.
We’re now going for the first time to diverge from the practical world of hardware into the theoretical world of mathematics, as we consider a very contentious topic in the world of audio. We live in a world in which it is now normal for audio to have some form of digital compression applied to it, some of which has an effect on what is played back through our speakers and headphones. When a compression algorithm changes what we hear, it’s distortion in audio terms, but how much is it distorted and how do we even measure that? It’s time to dive in and play with some audio files. Continue reading “Know Audio: Lossy Compression Algorithms And Distortion”→
These days, most of the media we consume is digital. We still watch movies and TV shows, but they’re all packaged in digital files that cram in many millions of pixels and as many audio channels as we could possibly desire.
Back in the day, though, engineering limitations meant that media on film or tape were limited to analog stereo audio at best. And yet, the masterminds at Dolby were able to create a surround sound format that could operate within those very limitations, turning two channels in to four. What started out as a cinematic format would bring surround sound to the home—all the way back in 1982!
It’s no secret that here at Hackaday we’ve at times been tempted to poke fun at the world of audiophiles, a place where engineering sometimes takes second place to outright silliness. But when a high quality audio project comes along that brings some serious engineering to the table we’re all there for it, so when we saw [Slyka] had published the files for their open source record lathe, we knew it had to be time to bring it to you.
Truth be told we’ve been following this project for quite a while as they present tantalizing glimpses of it on social media, so while as they observe, documentation is hard, it should still be enough for anyone willing to try cutting their own recordings to get started. There’s the lathe itself, the controller, the software, and a tool for mapping EQ curves. It cuts in polycarbonate, though sadly there doesn’t seem to be a sound sample online for us to judge.
CRT monitors: there’s nothing quite like ’em. But did you know that video projectors used to use CRTs? A trio of monochrome CRTs, in fact: one for each color; red, green, and blue. By their powers combined, these monsters were capable of fantastic resolution and image quality. Despite being nowhere near as bright as modern projectors, after being properly set up, [Technology Connections] says it’s still one of the best projected images he has seen outside of a movie theatre.
After a twenty-minute startup to reach thermal equilibrium, one can settle down with a chunky service manual for a ponderous calibration process involving an enormous remote control. The reward is a fantastic (albeit brightness-limited) picture.
Still, these projectors had drawbacks. They were limited in brightness, of course. But they were also complex, labor-intensive beasts to set up and calibrate. On the other hand, at least they were heavy.
[Technology Connections] gives us a good look at the Sony VPH-D50HT Mark II CRT Projector in its tri-lobed, liquid-cooled glory. This model is a relic by today’s standards, but natively supports 1080i via component video input and even preserves image quality and resolution by reshaping the image in each CRT to perform things like keystone correction, thus compensating for projection angle right at the source. Being an analog device, there is no hint of screen door effect or any other digital artifact. The picture is just there, limited only by the specks of phosphor on the face of each tube.
Converging and calibrating three separate projectors really was a nontrivial undertaking. There are some similarities to the big screen rear-projection TVs of the 90s and early 2000s (which were then displaced by plasma and flat-panel LCD displays). Unlike enclosed rear-projection TVs, the screen for projectors was not fixed, which meant all that calibration needed to be done on-site. A walkthrough of what that process was like — done with the help of many test patterns and a remote control that is as monstrous as it is confusing — starts at 15:35 in the video below.
Like rear-projection TVs, these projectors were displaced by newer technologies that were lighter, brighter, and easier to use. Still, just like other CRT displays, there was nothing quite like them. And if you find esoteric projector technologies intriguing, we have a feeling you will love the Eidophor.
Electret capsules can be found in some of the highest quality microphones for studio use, as well as in some of the very cheapest microphone capsules on the market. More care and attention has gone into the high-end capsule and its associated circuitry than the cheap one, but is it still possible to get good quality from something costing under a dollar? [Mubarak Basha] thinks so, and has designed a preamp circuit to get the best from a cheap electret capsule.
These capsules may be cheap, but with the addition of a low voltage supply, a resistor, and a capacitor, their internal FET delivers a decent enough input to many a project. To improve on that will need a bit of effort, and in this the preamp delivers by taking care to match impedance, impose a carefully chosen frequency response, and just the right gain to derive a line level output from the electret’s level. It’s hardly a complex circuit, but that’s not always necessary.
As always in these situations, without appropriate test equipment it’s difficult to gauge quality. We’d say this though, if you make one of these and it falls short, you won’t have spent much. Meanwhile if you’re curious about electrets, here’s our guide.
It’s been a while since the last installment in our Know Audio series, in which we investigated distortion as it applies to Hi-Fi audio. Now it’s time to return with part two of our look at distortion, and attempt some real-world distortion measurements on the bench.
Last time, we examined distortion from a theoretical perspective, as the introduction of unwanted harmonics as a result of non-linearities in the signal path. Sometimes that’s a desired result, as with a guitar pedal, but in a Hi-Fi system where the intention is to reproduce as faithfully as possible a piece of music from a recording, the aim is to make any signal path components as linear as possible. When we measure the distortion, usually expressed as THD, for Total Harmonic Distortion, of a piece of equipment we are measuring the ratio of those unwanted harmonics in the output to the frequencies we want, and the resulting figure is commonly expressed in dB, or as a percentage. Continue reading “Know Audio: Distortion Part Two”→
TOSLINK was developed in the early 1980s as a simple interface for sending digital audio over fiber optic cables, and despite its age, is still featured on plenty of modern home entertainment devices. As demonstrated by [DIY Perks], this old tech can even be taught some new tricks — namely, transmitting surround sound wirelessly.
Often, a TOSLINK stream is transmitted with a simple LED. [DIY Perks] realized that the TOSLINK signal could instead be used to modulate a cheap red laser diode. This would allow the audio signal to be sent wirelessly through the open air for quite some distance, assuming you could accurately aim it at a TOSLINK receiver. The first test was successful, with the aid of a nifty trick, [DIY Perks] filled the open TOSLINK port with a translucent plastic diffuser to make a larger target to aim at.
The rest of the video demonstrates how this technique can be used for surround sound transmission without cables. [DIY Perks] whipped up a series of 3D printed ceiling mirror mounts that could tidily bounce laser light for each surround channel to each individual satellite speaker.
It’s a very innovative way to do surround sound. It’s not a complete solution to wiring issues—you still need a way to power each speaker. Ultimately, though, it’s a super cool way to run your home theater setup that will surely be a talking point when your guests notice the laser mirrors on the ceiling.
