frnkp2000 said:
ETs of the day only yielded 15 minutes per side and were played laterally (inside out) as opposed to vertically (outside in). <I MAY have that backwards--it's been awhile.> Totally different type of stylus.
The lateral vs. vertical distinction had nothing to do with "outside-in" versus "inside-out."
On a vertically-cut disc (which is what most ETs were), the amplified audio signal causes the needle to dig down into the groove, creating a "hill-and-dale" groove that's replicated on playback. When coupled with the heavy stylus pressure needed to reproduce an ET, the result was a limited playback lifespan - you were literally grinding away the recorded "hills" with every playback.
(I believe commercial cylinder recordings were also cut vertically.)
On a laterally-cut disc, like a commercial 78 or later a 45 or LP, the amplified audio signal causes the needle to move back and forth in the groove, creating the familiar squiggles that you can see when you look at an LP under magnification. The louder the signal and deeper the bass response, the more the needle moves back and forth. When you're trying to pack 25 minutes' worth of grooves onto one side of a disc, there's a serious technical challenge involved in cutting the grooves small enough to fit, and to avoid very loud passages sending the needle right out of the groove into the disc space supposed to be occupied by the next concentric circle of the groove. It was the technical development of the "microgroove" system that finally became a commercial reality in 1948, and that's what's very properly being celebrated this year. While there had been experimental microgroove recordings prior to 1948, and even some limited commercial uses, there were no consumer microgroove formats prior to the introduction of the LP, which has proved to be by far the most durable consumer music format in the history of the industry.
As for inside-out versus outside-in, that's purely a function of which direction the turntable motor spins. The reason broadcast ETs were usually recorded inside-out had to do with the quality of the recording. Because discs spin at a constant angular velocity (33 rotations per second, for a typical broadcast ET), the needle is actually moving much faster linearly through the groove on the larger outside of the disc than on the smaller inside of the disc. And just as with tape recording, the faster the linear velocity of the recording medium, the better the high-frequency response. If you started recording an ET at the outside and let it play through to the inside, the audio quality (never that great to start with) would get grungier as you approached the inside of the disc and the end of the recording. And if you were using multiple 16-inch discs on multiple turntables to record a show longer than 15 minutes, the transition from the end of one disc (at the inside) to the start of the next could sound pretty lousy. By ending one disc at the higher-quality outside, you could then have a cleaner transition to the start of the next disc.