Know Audio: Stereo

September 21, 2022 by Jenny List 16 Comments

In our occasional series charting audio and Hi-Fi technology we have passed at a technical level the main components of a home audio set-up. In our last outing when we looked at cabling we left you with a promise of covering instrumentation, but now it’s time instead for a short digression into another topic: stereo. It’s a word so tied-in with Hi-Fi that “a stereo” is an alternative word for almost any music system, but what does it really mean? What makes a stereo recording, and how does it arrive at your ears?

From West London Trains, To 3D Audio

A steam train passing through a station, from a distance in black and white — The driver of this Great Western Railway train had no idea that he was making audio history.

As most of you will know, a mono recording uses a single microphone and a single channel while a stereo one uses two microphones recording simultaneously a left and right channel. These are then played back through a pair of speakers, and the result is a sense of spatial field for the listener. Instruments appear to come from their relative positions when recorded, and the sense of being in the performance is enhanced.

Stereo recording as we know it was first perfected as one of the many inventions credited to Alan Blumlein, then working for EMI in London. We have one of his stereo demonstration films in “Trains at Hayes“, filmed from the EMI laboratories overlooking the Great Western Railway, and featuring a series of steam-hauled trains crossing the field of view with a corresponding stereo sound field. His work laid down the fundamentals of stereo recording, including microphone configurations and what would become the standard for stereo audio recording on disk with the channels on the opposite sides of a 45 degree groove. Continue reading “Know Audio: Stereo” →

Equalize Your Listening With HiFiScan

September 12, 2022 by Jenny List 28 Comments

Audiophiles will go to such extents to optimize the quality of their audio chain that they sometimes defy parody. But even though the law of diminishing returns eventually becomes a factor there is something in maintaining a good set of equipment. But what if your audio gear is a little flawed, can you fix it electronically? Enter HiFiScan, a piece of Python software to analyse audio performance by emitting a range of frequencies and measuring the result with a microphone.

This is hardly a new technique, and it’s one which PA engineers have used for a long time to tune out feedback resonances, but an easy tool bringing it to the domestic arena is well worth a look. HiFiScan is a measuring tool so it won’t magically correct any imperfections in your system, however it can export data in a format suitable for digital effects packages.

Naturally its utility is dependent on the quality of the hardware it’s used with, but the decent quality USB microphone used in the examples seems to give good enough results. We see it used in a variety of situations, of which perhaps the most surprising is a set of headphones that have completely different characteristics via Bluetooth as when wired.

If audio engineering interests you, remember we have an ongoing series: Know Audio.

Hackaday Prize 2022: A Plasma Tweeter For Ultimate Clarity

August 8, 2022 by Jenny List 18 Comments

In the world of audio there are a huge variety of esoteric technologies which are rarely seen. One such is the plasma tweeter, a type of loudspeaker which generates sound by modulating a small electrical discharge. The benefit of this design comes in its delivering the closest possible to a point audio source, in effect the theoretical ideal speaker for treble frequencies. They’re a little hazardous due to the voltage but aren’t too difficult to make, as demonstrated by [Mircemk] whose version uses a recycled power pentode tube — which is how it showed up in the Hack it Back round of the Hackaday Prize.

It can be thought of as a cousin of the Tesla coil, with the same resonant oscillator but no capacity hat. Instead the top of the coil ends in a point, from which in the perfect speaker a ball of plasma replaces the Tesla’s impressive sparks. In this case the pentode is joined by a high-voltage TV line output transistor as a bias supply, which is in turn modulated with the audio through a small amplifier. It sometimes needs the plasma teasing out of it through discharge to a screwdriver, but the result is a very effective and clear plasma tweeter.

If plasma tweeters interest you, we’ve featured them before.

50-Year-Old 8-Track Changer Repair And Hack

July 25, 2022 by Chris Lott 28 Comments

For reasons still unclear, [Techmoan] has procured an RCA 8-track changer that holds five tape cartridges in a custom carrier. It somewhat works, but had a bit of mechanical issues here and there which needed some maintenance. Additionally, the player is designed for the US market and 60 Hz mains, but [Techmoan] is in the UK with 50 Hz.

Although electronics are used for the basic tape player portion, everything else is operated by mechanical gears, levers, and motors. The system plays both sides of each tape cartridge through to completion, and then switches automatically to the next one in the stack. Cartridges could be up to 90 minutes each, making for over seven hours of playing time. Oddly, the system does not repeat automatically after the fifth tape ends –operator intervention is required. It’s not entirely clear whether these carousels were primarily intended to play background music inside businesses, or built for niche consumer applications.

After discovering there was no setting to adjust the tape’s speed for 50/60 Hz operation, [Techmoan] could have ordered or fabricated a larger-diameter pulley for the motor drive shaft. But in true hacker style, he instead solves the problem with cellophane packing tape. By trial and error, he builds up the pulley diameter by winding lengths of tape until the music sounds just “good enough” to his ear. Then he pulls out the wow and flutter meter to really zero in — and gets it bang on. He says that this changer is needed for a future video, so we’re looking forward to see how it will be employed.

If you like these old mechanical logic controls, check out the video below the break. If you want dig into the workings of an 8-track player, check out Jenny List’s retro teardown from 2017. Does anyone still use 8-track tapes any more?

Continue reading “50-Year-Old 8-Track Changer Repair And Hack” →

Making A Projector Screen Out Of Flex Seal Works Okay, Kinda

June 10, 2022 by Lewin Day 6 Comments

Watching movies on the big screen is fun, but getting out to the cinema or drive-in can be a hassle. It’s possible to get the same experience at home with a little creativity, as shown in this DIY projector screen build by [The Hook Up].

The build started with a giant motorized roller screen designed for a patio. It was scored on the cheap as it was salvaged after removal from its original home. Having seen a screen door turned into a boat with the help of Flex Seal, [The Hook Up] was confident that the flyscreen could be sealed up and used for projection.

Right away, the going got tough. Light applications weren’t really filling in the holes in the flyscreen, while thick applications had major issues with runs. Eventually, the screen was painted with 3 gallons of white Flex Seal and hung up to test.

The runs caused issues, as the lumpy screen texture was distracting when viewing movies. Additionally, the glossy finish was creating unsightly reflections. After some trial and error, the issues were solved by sanding the Flex Seal surface flat and using matte clear spray paint to dull the shine.

The result was a grand projection screen that rolls down at the touch of a button, the likes of which we’ve seen before, though at significant cost. [The Hook Up] readily admitted that the several hundred dollars invested might have been better spent on buying a pre-made screen. Nonetheless, it’s a cool project, and we respect the creator for putting in the work! Video after the break.
Continue reading “Making A Projector Screen Out Of Flex Seal Works Okay, Kinda” →

Character VFD Becomes Spectrum Analyzer

May 24, 2022 by Lewin Day 7 Comments

These days, streaming services are a great way to listen to music or podcasts on your computer or on the go. However, they lack one feature of the MP3 players and streamers of old: visualizations! [mircemk] is a fan of those, and has built a hardware spectrum analyzer that pumps with the music.

The build relies on a 20×2 character VFD display that looks great, with high brightness and excellent contrast. It can be easily driven from a microcontroller, as it has a controller on board compatible with the typical HD44780 command set. On Arduino platforms, this means the display can easily be driven with the popular LiquidCrystal library.

The Arduino Nano inside takes in the audio signal via its analog inputs. It then processes the audio with the fix_fft library, which runs a Fast Fourier Transform in order to figure out the energy level of each frequency bin in the audio spectrum for both the left and right channels. This data is then sent to the screen for display. It’s impressively fast and smooth, with the display dancing along with the beat nicely as [mircemk] tests it out with some tunes.

If it looks familiar, it’s because it’s an updated version of a prior project from [mircemk]. We saw it previously as a VU meter that pulsed with the beat, an altogether simpler visualization but still a cool one. Video after the break.

Continue reading “Character VFD Becomes Spectrum Analyzer” →

Untangling The Maze Of Digital TV Upgrades

May 24, 2022 by Jenny List 24 Comments

When we all shifted our television broadcasts to digital, for a moment it looked as though we might have had to upgrade our sets only once and a set-top box would be a thing of the past. In Europe that meant the DVB-T standard, whose two-decade reign is slowly passing to DVB-T2 for higher definition and more channels. All of this might seem simple but for the DVB-T2 standard being a transport layer alone without a specified codec. Thus the first generation of DVB-T2 equipment uses MPEG4 or H.264, while for some countries the most recent broadcasts use HEVC, or H.265. [CyB3rn0id] is there to guide us through the resulting mess, and along the way produce a nifty upgrade that integrates a set-top box on the back of an older DVB-T set.

Simply bolting a set-top box to a TV is not the greatest of hacks, however this one takes matters a little further with a 3D printed bracket and an extension which brings the box’s IR receiver out to the front of the TV on a piece of prototyping board. Along with a laptop power supply plumbed directly into the TV, it gives new life into a set which might otherwise have been headed for landfill.

As long-time readers will know, we quite like a TV retrofit here at Hackaday.