How to pack a stereo signal in one record groove

Now <i>there</i> is something Bartosz Ciechanowski should write a blog post about!<p>I also think something important is missing from this explanation: the vertical&#x2F;horizontal solution would not have been backwards compatible in two ways: (1) A mono needle would not have been able detect the vertical movement, resulting in a missing channel. (2) A stereo needle able to play such a record would not have been able to play a classic mono record, because the mono signal would have only been translated into a single channel (the left or right channel), and the other channel would have remained silent.<p>(1) would&#x27;ve made stereo records unattractive for customers who already owned an existing mono player, and (2) would&#x27;ve made stereo players unattractive to customers who already had a substantial mono record collection.<p>With the 45 degree solution, existing mono players were able to play stereo records (the horizontal movement is exactly the sum of the two channels), and stereo players were able to play existing mono records. For this to work, the left and right signals were recorded in opposite phase. A really elegant solution, which somehow reminds me of the cover of GEB [0].<p>PS: if you are interested in cutting-edge record groove technology, the &quot;Füllschriftverfahren&quot; invented by Eduard Rhein might interest you. It was an early compression technology for audio. The method was based on earlier work by the London-based Columbia Graphophone Company, but their work was never used in practice. Basically, before this invention, the spacing between the grooves on a record was fixed, with enough margins so that large amplitudes would not cut into neighboring grooves. Rhein build a machine that dynamically spaced the grooves based on the maximum local amplitude, allowing much smaller groove margins for quiet parts of an audio file, and therefore increased information density. This nearly doubled the running time of typical records.<p>Sadly, I only found an extensive description of this technology in German, including original patents [1]. But the figures are self-explaining.<p>[0] <a href="https:&#x2F;&#x2F;i.stack.imgur.com&#x2F;OKBvZ.jpg" rel="nofollow">https:&#x2F;&#x2F;i.stack.imgur.com&#x2F;OKBvZ.jpg</a><p>[1] <a href="https:&#x2F;&#x2F;grammophon-platten.de&#x2F;page.php?530" rel="nofollow">https:&#x2F;&#x2F;grammophon-platten.de&#x2F;page.php?530</a>

This is one of those things I never gave much thought but is super facinating. The technology connections youtube channel just did a video about this, too: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3DdUvoc7tJ4">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3DdUvoc7tJ4</a>

I was recently in a large shop that sells books, music, etc. and I was <i>amazed</i> at the number of &quot;LPs&quot; (as I used to call them) of music old and new. The one thing that I really like about that format is... cover art. Cover art kind of survived the CD but the large size of a 12&quot; record sleeve means you get real art.<p>I asked someone way younger than me (some students of about 19&#x2F;20) why they buy records and they expressed how much they like the physical format and owning the music.

A few years back I had the privilege of working for the New York City edition of the Red Bull Music Academy, and, perhaps unsurprisingly, a large portion of the lectures and general discussion focused on things related to vinyl.<p>One thing I remember standing out to me was a mention by a vinyl mastering engineer that he would manually roll up the bass level on the EQ over the length of the side as the record was cut. He explained that this was because on most record players the tonearm is more or less parallel to the groove at the start of the side and by the end of the side is less so, which decreases bass response, requiring more bass energy in the signal to compensate.

Quadraphonic CD-4 records from the 1970&#x27;s encode 4 discrete channels into a single record groove!<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Compatible_Discrete_4" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Compatible_Discrete_4</a><p>The trick is to encode two additional channels on a 30kHz carrier signal above human hearing range, then demodulate those channels in the receiver.

I will add that the “mid-side” technique is used elsewhere, besides record grooves:<p>- In compressed audio file (such as MP3)<p>- In signal processing chains in the studio (process mid and side channels separately, then convert back to L&#x2F;R)<p>- In certain stereo microphone recording techniques (there is a type of microphone which records left and right, but with opposite phase)

Aside from the contents, let&#x27;s all take a moment to admire the simplicity of this page. A few animated pictures and everybody got right away what&#x27;s going on. Absolutely amazing!

Hm, I thought that stereo vinyl records are recorded in a way that vertical groove profile is V=L+R and the horizontal represents H=L-R. It&#x27;s backward compatible with older mono gramophones that read only L+R and stereo players do H+V=2L and H-V=2R to decode.<p>Also, while writing this, I realised that it&#x27;s exactly the same as in the article. Just another way of thinking about it.

My great &#x27;aha&#x27; moment of &#x27;technology is actually sometimes really simple when broken down&#x27; was realizing that magnetic sound recording is just running past a speaker coil at a constant speed while holding something long and ferrous next to it. To play it back do the same thing but plug the coil into the input.

Then encode a surround sound signal as a Dolby Pro Logic II stereo signal and you’ve got a surround sound record!<p><a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Dolby_Pro_Logic" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Dolby_Pro_Logic</a><p>DPLII was based on the fact that if you invert one channel of a stereo signal, it sounds effectively the same. So, they had some way of encoding front and back signals as some sort of symmetry&#x2F;anti-symmetry between the left and right signal.

This is an amazing example of moving forward without breaking changes ... We could probably do better with our software too. Another interesting example of creating a compatible signal is the addition of chroma information to the black and white NTSC television signal. The original signal was modulated using VSBAM and the chroma signal was added to (predominantly) the high frequencies of the channel.

Another reason why mono is better for 12&quot; dance records (another being avoiding stereo image&#x2F;balance effects in clubs; and if the PA setup is mono anyway then you&#x27;ll get a real mono mix rather than a summed stereo mix.)<p>I imagine stereo could help a bit with phase effects between speakers, but they would likely still be an issue in multi-speaker setups.

It sounds antithetical to the analog nature of vinyl, but has anyone experimented with digital audio on vinyl?

Trivia: well into the 1970s, promotional copies of hit songs were released to U.S. radio and record stores on vinyl 7-inch 45 RPM format, one side in mono, and one side in stereo.

I love nineties styled websites. Clear and precise.

Very clear visual. Does anyone have a similar visual reference for how quadraphonic records work?

Or stereo signal coming from a single cable.

But wait till you see quadrophonic records!

That all looks erotic.

OK, now do quadraphonic...