Retrotechtacular: Stereo Records
The 20th century saw some amazing technological developments. We went from airplanes to the moon. We went from slide rules to digital computers. Crank telephones to cell phones. But two of the most amazing feats of that era were ones that non-technical people probably hardly think about. The transformation of radio and TV from mono and black and white, to stereo and color. What was interesting about both of these is that engineers managed to find a way to push the new better result into the same form as the old version and — this is the amazing part — do it in such a way that the old technology still worked. Maybe it is the rate that new technology moves today, but we aren’t doing that today. Digital TV required all-new everything: transmitters, receivers, frequencies, and recording gear. Good luck trying to play the latest video game on your 25-year-old PC.
It is hard to remember when stores were full of all sorts of audio and video media. We’ve noticed that all forms of media are starting to vanish. Everything audio and video are all streamed or downloaded these days. Records, 8-tracks, cassettes, and even CDs and DVDs are vanishing. However, vinyl records have made a come back in the last few years for their novelty or nostalgic value.
Audio recording on wax, foil, or vinyl was more or less the same process perfected by [Thomas Edison] (or, perhaps, people who worked for him) back in 1877 although the flat records we think of didn’t appear until around 1890.
The principle is simple. Air pressure from sound cuts a groove into the recording medium. A piezoelectric stylus (or later, a stylus with a dynamic element) traced the groove and reproduced the same sound. Amplify it, and the phonograph is in business. You might enjoy the gramophone [SynthDan1] restored in the video below.
Stereo
By the 1950s, the hackers of their day were building or buying “hi-fi” equipment, gear that sounded better than the poor-quality audio spewing out of record players and AM radios of the day. Eventually, companies would roll out stereo recordings. But the records didn’t look any different, and they would still play on a standard (mono) record player. How is that possible? No, it isn’t two separate records like the vintage player at the top of this post found in the Museum of Technology in Paris.
We could explain it, but it is more fun to let [Bob Banks] from RCA explain it in this vintage advertisement.
The Real Story
Pretty impressive special effects for the time. [Bob] did oversimplify a few things, though. First, the groove can have a vertical component and a horizontal component. But the resolution on the vertical isn’t nearly as good, so that means one channel would be disadvantaged. Instead, the two tracks in the single groove are spun 45 degrees so that each channel has some horizontal and some vertical component.
[Bob] wants you to think RCA invented this, although he never actually says that flat out. In fact, [Alan Blumlein] of EMI patented the scheme back in 1931. The first commercial stereo records, which were not from RCA either, would not appear until 1957.
Because of how the groove was rotated, the movement of the stylus horizontally was the combination of the left and right tracks — the same as the mono signal. The vertical motion carried the difference: the left channel minus the right channel, or L-R.
That’s how a mono record could play back normally on a stereo player. The horizontal motion on the track will reproduce the same sound on both channels. Conversely, a mono stylus reading a stereo track would only pick up the horizontal part of the track and play both channels together. Unfortunately, many mono players didn’t move up and down very well and could wear a stereo record, so users learned not to play stereo records on mono players, even though it would work. Of course, that assumes you have the same-sized grooves. Older records had wider grooves and wider needles.
If you want to see how a stereo cutter works, check out [EpicenterBryan’s] video below.
Compatibility
In a market where Elvis Presley was still selling 78 RPM records because his fans couldn’t afford new record players, this compatibility was very important. We imagine [Alan Blumlein] would be horrified to see how we routinely tell everyone to throw away their tapes for CDs and their CDs for digital music. TV was the same. Making a signal with color that black and white sets could still receive was quite the marvel (and a topic for a future Retrotechtacular). The idea of making everyone throw out their sets for new ones or buy government-subsidized converters would have been poorly received, indeed.
We can’t help but wonder if we are doing all we can on compatibility. Do we really have to trash operating systems and CPUs every few years? Do we really need to double the memory in our phones every time our contracts run out? Or is it a clever planned obsolescence ploy? As people who create things, how are we doing on compatibility? We’ll see how history judges.
Featured image by [ParameterBond], Public Domain
Filed under: Hackaday Columns, History
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