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>