WEBVTT Kind: captions Language: en 00:00:00.190 --> 00:00:02.100 I don’t know if you’ve realized this… 00:00:02.100 --> 00:00:05.567 but vinyl records have gotten pretty popular! 00:00:05.567 --> 00:00:09.288 Analog is just so much more… real, man. 00:00:09.288 --> 00:00:16.526 And just like those newfangled streaming music services that can put a different audio signal into each of your airpods so the music can do 00:00:16.526 --> 00:00:20.003 cahraaazy effects like that [pans rapidly left and right] 00:00:20.003 --> 00:00:22.710 ye old LPs... 00:00:22.710 --> 00:00:25.102 they hold stereo sound. 00:00:25.725 --> 00:00:27.534 That’s kinda weird, though, isn’t it? 00:00:27.534 --> 00:00:31.791 Like, stereophonic means we have two audio channels. 00:00:31.791 --> 00:00:39.075 And if you look to other old sound formats, you’ll find two separate audio tracks to carry those two channels. 00:00:39.075 --> 00:00:43.461 The audio head of a compact cassette deck has two distinct pickups, 00:00:43.461 --> 00:00:49.145 each one detecting the signal on a dedicated left and right audio track contained on the tape. 00:00:49.145 --> 00:00:57.176 Same goes for reel-to-reel tape recorders, though here the heads are separated and the left and right channels are interleaved on the tape for... 00:00:57.176 --> 00:00:57.950 reasons. 00:00:57.950 --> 00:01:03.235 The analog soundtrack on motion picture film prints has two obvious channels, as well. 00:01:03.235 --> 00:01:10.180 And skipping ahead to the digital age, the datastream encoded on a compact disc contains two distinct audio channels 00:01:10.180 --> 00:01:13.757 that are decoded and reproduced by the CD player upon playback. 00:01:13.757 --> 00:01:17.516 Same goes for pretty much every digital sound format since. 00:01:17.516 --> 00:01:23.195 But a record like this has but the one groove that's played by a single stylus. 00:01:23.195 --> 00:01:27.591 Somehow, the action of dragging that single stylus through the single groove 00:01:27.591 --> 00:01:33.845 results in two audio channels that make the listening experience just that more real. 00:01:33.845 --> 00:01:35.581 What’s going on, here? 00:01:35.581 --> 00:01:42.520 Well, you might think it could be some sort of sound signal modulation trickery, but it’s actually much simpler than that. 00:01:42.520 --> 00:01:47.179 You probably already know that the groove wiggles the stylus to make the sound signal. 00:01:47.179 --> 00:01:50.700 And it turns out there’s more than just one way to wiggle. 00:01:50.700 --> 00:01:57.297 I covered this way way back when this channel was just a baby, but I didn’t really give it the time it’s worthy of. 00:01:57.297 --> 00:01:59.057 So I’m doing it now! 00:01:59.229 --> 00:02:01.210 Speaking of going way way back, 00:02:01.210 --> 00:02:07.070 Thomas Edison’s original phonograph pressed sound vibrations into a wax cylinder. 00:02:07.070 --> 00:02:12.032 A sound-collecting horn led to a diaphragm that would vibrate just like your eardrums do 00:02:12.032 --> 00:02:15.130 in response to changing sound pressure levels. 00:02:15.130 --> 00:02:22.980 That diaphragm was then attached to a sharp stylus which would copy those vibrations as a rapid up-and-down motion. 00:02:22.980 --> 00:02:30.535 When this stylus was pressed into a rotating soft wax cylinder, it would carve a groove into the surface of the wax. 00:02:30.535 --> 00:02:37.140 Moving that stylus laterally across the rotating cylinder created a long, spiral groove. 00:02:37.140 --> 00:02:44.146 And all the while it carved the groove, sound vibrations collected by the horn caused the stylus to move up and down, 00:02:44.146 --> 00:02:50.233 and the resulting variations in the groove’s depth would become a record of those sound vibrations. 00:02:50.834 --> 00:02:53.334 That’s why it’s called a record! 00:02:53.334 --> 00:02:55.643 I’m skipping over plenty of details here, 00:02:55.643 --> 00:03:03.489 but a mold could be made of this soft wax record so that resilient copies, like this, could be mass produced. 00:03:03.489 --> 00:03:09.656 Spin this record below a reproducing phonograph and its stylus, as it floats over the bumpy groove, 00:03:09.656 --> 00:03:14.026 will move up and down in the same manner as the recording stylus did. 00:03:14.026 --> 00:03:19.699 That imparts vibrations in a second diaphragm which makes tiny little sound pressure waves, 00:03:19.699 --> 00:03:24.241 and with the help of an amplifying horn the recorded sound could be reproduced. 00:03:24.950 --> 00:03:31.275 [very warbly, low-fidelity violin playing] 00:03:32.177 --> 00:03:35.486 Not terribly well, but it’s the 19th century still. 00:03:35.486 --> 00:03:37.208 Don’t expect too much. 00:03:37.208 --> 00:03:39.643 But then, this guy Berliner was like 00:03:39.643 --> 00:03:42.071 “Cylinders? Really?” 00:03:42.071 --> 00:03:44.202 and he thought of a better way to do this. 00:03:44.202 --> 00:03:50.506 Instead of wiggling a stylus up and down, you could do a side-to-side wiggle instead. 00:03:50.506 --> 00:03:58.917 That would allow you to carve a deep, spiral groove into the surface of a flat disc which would simplify everything a great deal. 00:03:58.917 --> 00:04:05.054 For starters, mass-producing hollow, cylindrical records with fine details on its surface, 00:04:05.054 --> 00:04:08.482 although Edison did figure it out, was, uh 00:04:08.482 --> 00:04:10.080 quite the process. 00:04:10.080 --> 00:04:13.537 A flat disc, meanwhile, could simply be stamped. 00:04:13.537 --> 00:04:16.368 Much cheaper, easier, and faster. 00:04:16.368 --> 00:04:22.457 Discs were also much easier to handle, less fragile than cylinders, and took up a fraction of the space 00:04:22.457 --> 00:04:25.349 in part because you could also - get this - 00:04:25.349 --> 00:04:29.446 put a second recording on the other side of the disc! 00:04:29.446 --> 00:04:30.953 Whoah. 00:04:30.953 --> 00:04:35.943 A side-to-side wiggly groove also greatly simplified the record players. 00:04:35.943 --> 00:04:41.105 Edison’s design needs a worm gear to move the reproducing assembly along 00:04:41.105 --> 00:04:48.797 because any significant weight on the groove would destroy the recording - so the stylus just floats over the cylinder. 00:04:48.797 --> 00:04:54.777 But the reproducer of disc phonographs was free to rest all its weight directly on the record. 00:04:54.777 --> 00:04:58.619 It was the walls of the groove that held the sound, not the floor, 00:04:58.619 --> 00:05:03.759 so a steel needle could simply drag along the bottom without damaging the recording 00:05:03.759 --> 00:05:09.338 (although playing a record would wear down that needle and you needed to replace it quite frequently). 00:05:09.338 --> 00:05:15.373 Needles were cheap, though, and this arrangement meant the groove would advance the reproducer all by itself, 00:05:15.373 --> 00:05:20.113 eliminating the need for the worm gear mechanism and its associated complexity. 00:05:20.113 --> 00:05:26.972 The disc was obviously the better option so much to Edison’s chagrin the cylinder was done for. 00:05:26.972 --> 00:05:32.851 As the years went on and we developed electronic sound amplification (thanks in no small part to radio), 00:05:32.851 --> 00:05:39.872 record players started using much smaller and lighter tone arms fitted with these newfangled phonograph pickups 00:05:39.872 --> 00:05:46.300 which turned the groove’s wiggling into an electrical signal that we would then amplify and pump into loudspeakers. 00:05:47.030 --> 00:05:48.608 There’s a few different ways we can do that, 00:05:48.608 --> 00:05:53.077 including attaching the stylus to a magnet which moves within a coil of wire, 00:05:53.077 --> 00:05:57.665 therefore producing a teeny bit of voltage in that wire as it vibrates. 00:05:57.665 --> 00:06:01.310 But you could also attach the stylus to the wire instead of the magnet, 00:06:01.310 --> 00:06:03.880 or even use piezoelectric crystals. 00:06:03.880 --> 00:06:06.376 There were a ton of ways we tried doing this. 00:06:06.376 --> 00:06:14.960 Anyway, soon, the tone arms and pickups would become so light that a tiny little sapphire or diamond stylus could be used. 00:06:15.325 --> 00:06:20.153 That allowed for the use of softer record materials with much smaller grooves 00:06:20.153 --> 00:06:25.701 that extended the runtime of recordings while also increasing audio fidelity. 00:06:25.701 --> 00:06:30.000 But the fundamental basics of the technology hadn’t changed at all. 00:06:30.000 --> 00:06:36.260 Sound was still stored in the walls of the groove, wiggling the stylus left and right as it flew by. 00:06:36.260 --> 00:06:42.051 A bunch of refinements over fifty years or so improved the process and made it sound better than ever 00:06:42.051 --> 00:06:46.150 but it was still the same concept as Berliner’s original discs. 00:06:46.150 --> 00:06:52.766 All we’ve really accomplished is make the groove’s wiggling more precise so it can better capture the nuances of a sound recording, 00:06:52.766 --> 00:06:58.819 and we made the thing that the groove wiggles more sensitive to its wiggling so it can reproduce it just as wiggly-well. 00:06:58.819 --> 00:07:04.015 However, now that we’ve made the tone arm so light and the stylus so small, 00:07:04.015 --> 00:07:07.809 we don’t have to worry about damage to the record nearly as much. 00:07:07.809 --> 00:07:11.633 And since this world we live in is three-dimensional, 00:07:11.633 --> 00:07:19.459 we could fit a second signal into the same groove if we revisit Edison’s idea and add a little… 00:07:19.459 --> 00:07:20.809 depth. 00:07:20.809 --> 00:07:26.160 When playing a record, the groove’s direction of motion takes up one of our three dimensions, 00:07:26.160 --> 00:07:30.460 but we still have two axes of motion available to the stylus. 00:07:30.460 --> 00:07:34.886 If we designed a pickup which could generate two independent signals from the stylus: 00:07:34.886 --> 00:07:39.129 one for its lateral movement and another for its vertical movement, 00:07:39.129 --> 00:07:43.501 we could recover a stereo signal from a single groove. 00:07:43.501 --> 00:07:45.403 So that’s what we did. 00:07:45.700 --> 00:07:46.730 Sort of. 00:07:47.009 --> 00:07:50.650 What I just described is more than a little askew with reality. 00:07:50.650 --> 00:07:52.539 I’ll explain in a moment. 00:07:52.539 --> 00:07:55.507 It turns out that English engineer Alan Blumlein, 00:07:55.507 --> 00:07:58.844 who basically created the concept of stereo sound, 00:07:58.844 --> 00:08:08.452 would describe in a 1931 patent the exact method by which stereo records would eventually be made starting in the late 1950’s. 00:08:08.452 --> 00:08:10.131 Pretty wild. 00:08:10.131 --> 00:08:15.740 Stereo records do contain a combination of vertical and lateral movement in their grooves, 00:08:15.740 --> 00:08:17.531 but it’s a bit more complicated than 00:08:17.531 --> 00:08:21.901 “the left channel is vertical movement and the right channel is lateral movement.” 00:08:21.901 --> 00:08:25.211 That would work, but not very well. 00:08:25.509 --> 00:08:31.429 For a start, the two channels would sound quite different from one another due to differing distortion profiles, 00:08:31.429 --> 00:08:34.392 so you couldn’t get a very pleasant recording. 00:08:34.392 --> 00:08:39.673 And secondly, a record made this way wouldn’t work with a conventional phonograph. 00:08:39.673 --> 00:08:48.723 Up ‘til now, the groove only ever wiggled left and right, so that’s the only direction of movement a conventional phonograph cartridge can detect. 00:08:48.723 --> 00:08:53.655 If an uppy-downy lefty-righty stereo record was placed on an old record player, 00:08:53.655 --> 00:08:58.899 you’d only hear whichever channel was the lefty-righty one - and nobody wants that. 00:08:58.899 --> 00:09:03.209 So instead, we take that up-down-left-right concept and go like this. 00:09:03.617 --> 00:09:04.679 *wrooup* 00:09:05.130 --> 00:09:10.259 Now, each of the two channels is recorded on the disc as a diagonal movement, 00:09:10.259 --> 00:09:15.477 and the walls of the grove will sort of move the stylus around every which way. 00:09:15.477 --> 00:09:23.501 To detect this two-dimensional movement, a stereo phonograph cartridge has two pickups placed at right-angles to one another. 00:09:23.501 --> 00:09:31.913 Both pickups share the single stylus, and this whole contraption is set at a 45 degree offset with respect to the groove. 00:09:31.913 --> 00:09:33.202 With this arrangement, 00:09:33.202 --> 00:09:38.148 each pickup is affected by both vertical and horizontal movement. 00:09:38.148 --> 00:09:42.123 And when you hear that, you might wonder how this works at all. 00:09:42.123 --> 00:09:45.916 See, when we want to generate a signal on only the left channel, 00:09:45.916 --> 00:09:50.794 the stylus needs to move back and forth in a downward and leftward motion. 00:09:50.794 --> 00:09:54.310 Doing that will only cause movement in one of the pickup coils, 00:09:54.310 --> 00:09:57.143 with the other one oblivious to what’s happening. 00:09:57.143 --> 00:10:00.766 Then, of course, the stylus needs to vibrate along the opposite diagonal, 00:10:00.766 --> 00:10:02.963 in a downward and rightward motion, 00:10:02.963 --> 00:10:05.814 to produce a sound on only the right channel. 00:10:05.814 --> 00:10:11.032 This might sound bonkers and overly complicated, but this arrangement has several advantages. 00:10:11.032 --> 00:10:15.055 First, it works perfectly with old, mono recordings. 00:10:15.055 --> 00:10:20.681 When playing a mono record, its purely lateral vibrations will affect both pickups equally 00:10:20.681 --> 00:10:25.546 and produce an essentially identical signal in the left and right channels. 00:10:25.546 --> 00:10:31.926 You won’t have to deal with one dead channel which nobody likes; both channels will play the same thing. 00:10:31.926 --> 00:10:38.548 Better yet, the 45 degree offset means that so long as we are careful in the mastering process, 00:10:38.548 --> 00:10:44.701 we can produce stereo records that are actually backward-compatible with mono phonographs. 00:10:44.701 --> 00:10:47.037 Just like in the acoustic phonograph days, 00:10:47.037 --> 00:10:53.630 the process of making a record starts by carving a spiral groove in a blank disc with a cutting stylus, 00:10:53.630 --> 00:11:00.850 but now that stylus is hooked up to high-speed actuators that precisely vibrate it based on an audio signal. 00:11:00.850 --> 00:11:05.181 For stereo recordings, the cutting stylus is attached to two actuators, 00:11:05.181 --> 00:11:06.781 one for each channel, 00:11:06.781 --> 00:11:11.422 that are arranged with the same 45 degree offset of the playback cartridge. 00:11:11.422 --> 00:11:16.369 The actuator for the left channel vibrates the cutting stylus diagonally, downward and leftward, 00:11:16.369 --> 00:11:19.993 with the right channel actuator cutting in the opposite diagonal. 00:11:19.993 --> 00:11:22.537 And here’s why this is such a big deal: 00:11:22.537 --> 00:11:29.382 So long as we ensure the correct signal polarity, when the left and right channel signals are identical, 00:11:29.382 --> 00:11:35.701 that will cancel out vertical movement of the cutting stylus and we will only get lateral movement. 00:11:35.701 --> 00:11:39.742 See, if this actuator is pushing while the other is pulling, 00:11:39.742 --> 00:11:43.449 both of those actions result in the stylus moving to the left, 00:11:43.449 --> 00:11:50.957 but the downward motion imparted by this actuator is perfectly canceled out by the upward motion of the other. 00:11:50.957 --> 00:11:58.582 The cutting head will only move vertically when there is a difference in intensity between the two signals the actuators receive, 00:11:58.582 --> 00:12:02.490 as that causes an imbalance in pulling force between them. 00:12:02.490 --> 00:12:08.941 See, stereo sound could be made from two completely independent signals like we see in magnetic tape, 00:12:08.941 --> 00:12:14.984 but it can also come from a mono signal combined with a stereo-difference signal. 00:12:14.984 --> 00:12:24.841 And that’s what’s actually contained on a stereo record — it’s a mono signal feeding both loudspeakers equally when the groove moves side-to-side, 00:12:24.841 --> 00:12:32.077 but when there’s some vertical movement goin’ on, the signal gets pushed towards the left or the right channel. 00:12:32.077 --> 00:12:34.540 Now, of course, this is happening instantaneously, 00:12:34.540 --> 00:12:37.729 so it’s not like we’re just panning a signal left and right; 00:12:37.729 --> 00:12:43.386 every individual movement in the stylus — meaning every sound detail the record contains 00:12:43.386 --> 00:12:48.329 — can be pushed to the left or the right channel and to virtually any degree. 00:12:48.329 --> 00:12:49.940 Just gotta do a little extra wiggling. 00:12:50.413 --> 00:12:54.473 And I should say it’s not like there’s any signal processing going on here, 00:12:54.473 --> 00:12:58.363 that’s just how the signals get generated in a stereo cartridge 00:12:58.363 --> 00:13:04.839 when this more complex groove moves the stylus around in two dimensions rather than just one. 00:13:04.839 --> 00:13:12.949 But the vertical component arguably doesn’t contain any sound information; it just pushes the sound towards the left or the right channel. 00:13:14.882 --> 00:13:18.310 I’m sure semantics discussions in the comments will be fantastic. 00:13:18.310 --> 00:13:23.868 Anyway, aside from this method doing a fine job of making a stereo signal possible, 00:13:23.868 --> 00:13:28.428 if you play one of these new stereo records on an old mono phonograph, 00:13:28.428 --> 00:13:33.610 well you won’t get stereo sound, obviously, but you won’t be missing anything either. 00:13:33.610 --> 00:13:39.257 A sound that’s only supposed to be on the left channel still vibrates the stylus left and right, 00:13:39.257 --> 00:13:42.118 and the same goes for right-channel sounds. 00:13:42.118 --> 00:13:46.507 So old mono phonographs will still let you hear everything on the record, 00:13:46.507 --> 00:13:50.370 meaning these new stereo records are backward compatible. 00:13:50.370 --> 00:13:57.311 The vertical component in their grooves just doesn’t do anything because an older phonograph doesn’t know what that is. 00:13:57.311 --> 00:13:59.480 It has no means to detect it. 00:13:59.480 --> 00:14:04.138 Now, if we flipped the polarity of one of the actuators in the cutting process, 00:14:04.138 --> 00:14:08.888 then equal signal intensity on both channels would cancel out lateral movement 00:14:08.888 --> 00:14:12.374 and would be recorded purely as changes in depth. 00:14:12.374 --> 00:14:16.662 We’d still get a kind-of functional stereo record out of this, 00:14:16.662 --> 00:14:22.000 but it would sound extremely weird, especially when played on a mono phonograph. 00:14:22.000 --> 00:14:25.960 Mono record players would only pick up sounds that are panned left or right, 00:14:25.960 --> 00:14:29.560 and anything in the virtual center would be silent. 00:14:29.560 --> 00:14:34.575 That’s effectively what listening to the raw stereo-difference channel would sound like - 00:14:34.575 --> 00:14:36.959 and here, I can simulate this in Audacity! 00:14:36.959 --> 00:14:39.346 Let’s see, just split out the track, 00:14:39.346 --> 00:14:42.246 invert one of em, smoosh it back together into mono, 00:14:42.246 --> 00:14:45.686 OK, here’s what the recording normally sounds like: 00:14:46.481 --> 00:14:48.265 ♫ some percussion ♫ 00:14:48.630 --> 00:14:53.003 ooh now there's a groovy bass line! 00:14:55.387 --> 00:14:57.356 cymbals build, got some congas, 00:14:57.356 --> 00:15:00.000 MM, got some HORNS! 00:15:01.766 --> 00:15:02.687 ba da ba da 00:15:02.687 --> 00:15:03.371 ba da ba da 00:15:03.371 --> 00:15:04.403 ba dum... 00:15:04.403 --> 00:15:07.330 And here’s a simulated stereo-difference channel. 00:15:07.781 --> 00:15:11.671 ♫ same percussion, but now it's weirdly muffled and sounds like it's coming from a distant bathroom ♫ 00:15:13.776 --> 00:15:15.985 hey wait where'd the bass line go? 00:15:15.985 --> 00:15:17.494 cymbaaalllLLLLSSSS, 00:15:17.494 --> 00:15:18.745 HORNS 00:15:20.764 --> 00:15:24.890 So it's the same song, for sure, but it's, like... 00:15:24.890 --> 00:15:25.992 haunted. 00:15:27.904 --> 00:15:31.513 So, that’s what’s going on with stereo records. 00:15:31.513 --> 00:15:38.102 In a way, it’s a clever combination of Edison’s original idea and Berliner’s improvement. 00:15:38.102 --> 00:15:43.125 I don’t think Alan Blumlein was thinking of that at all when he first concocted this idea, 00:15:43.125 --> 00:15:46.203 but that won’t stop me from making the connection. 00:15:46.203 --> 00:15:49.060 Now, this method is not perfect. 00:15:49.060 --> 00:15:55.903 Complete stereo channel separation just isn’t possible when your sound is coming from physical movements. 00:15:55.903 --> 00:16:00.981 Even if you nailed the angles just right and the record was mastered perfectly, 00:16:00.981 --> 00:16:06.990 some vibrations from one of the pickups are liable to make their way through the cartridge and into the other. 00:16:06.990 --> 00:16:11.390 So no matter how staunchly someone defends the sound of vinyl, 00:16:11.390 --> 00:16:16.149 records are objectively pretty bad at isolating the two channels. 00:16:16.149 --> 00:16:22.525 But it’s still really clever, and the effect of having two channels is just that - an effect. 00:16:22.525 --> 00:16:26.953 It doesn’t need to be perfect to make a huge difference to the listening experience. 00:16:28.929 --> 00:16:30.000 Ya like jazz? 00:16:30.910 --> 00:16:33.741 ♫ distortedly smooth jazz ♫ 00:16:38.166 --> 00:16:42.515 And secondly, a record made this way wouldn’t work at all with conven-- 00:16:42.515 --> 00:16:43.578 I shouldn’t add that, 00:16:43.578 --> 00:16:45.101 Don’t add words! 00:16:45.101 --> 00:16:46.739 ...signal possible. 00:16:46.739 --> 00:16:50.606 If you play one of these new stereo records on a old mono phonogr - 00:16:50.606 --> 00:16:51.871 aw, crap 00:16:52.537 --> 00:16:58.381 Spin this sound record below a reproducing phonograph and its stylus as it fff… 00:16:59.605 --> 00:17:00.947 [defeated] 00:17:00.947 --> 00:17:04.282 …and do cahraaaaaazy effects like that, 00:17:04.282 --> 00:17:08.549 ye old LPs hold [clank] 00:17:10.289 --> 00:17:11.129 dangit 00:17:11.129 --> 00:17:16.472 cahraaaaaazy effects like that, ye old LPs… 00:17:16.794 --> 00:17:17.805 [clank] 00:17:17.805 --> 00:17:19.016 I just did it again! 00:17:20.648 --> 00:17:24.854 So normally, I'd put some sort of gag here, but this time, I think we should do it 00:17:24.854 --> 00:17:27.315 IN IN STEREO STEREO 00:17:27.315 --> 00:17:30.158 THAT'S RIGHT, TWO THAT'S RIGHT, TWO CAPTIONS, ONE FOR EACH EYE CAPTIONS, ONE FOR EACH EYE! 00:17:30.158 --> 00:17:33.576 HOLD YOUR PHONE UP TO YOUR HOLD YOUR PHONE UP TO YOUR FACE AND IT'S IN 3D! FACE AND IT'S IN 3D! 00:17:34.070 --> 00:17:35.973 just kidding, don't you look silly!