WEBVTT 1 00:00:18.920 --> 00:00:20.280 Hey Ben. 2 00:00:20.280 --> 00:00:21.440 Hey Matt. 3 00:00:21.440 --> 00:00:24.000 It has been a while, hasn't it? 4 00:00:24.000 --> 00:00:25.010 Been a bit. 5 00:00:25.010 --> 00:00:36.820 I mean, not for our listener, obviously. Our listener, it's just been a month. But for us, things... life has overtaken us. A lot of things are going on. We are, in fact, on different continents right now. 6 00:00:36.820 --> 00:00:49.160 And I'm looking at my sound levels, in fact, and I'm wondering how awful this is going to sound. So I'm going to just tweak something. But, yeah, I apologize in advance to the poor editor who has to edit this because I am recording... 7 00:00:49.160 --> 00:01:03.700 on my laptop from my wife's childhood home in her bedroom where she grew up in Birmingham in the UK, which is not where I was planning on being around this time. 8 00:01:03.700 --> 00:01:03.820 Mm-hmm. 9 00:01:03.820 --> 00:01:09.600 But nevertheless, adult things happen and you end up in a different landmass. So that's me. 10 00:01:09.600 --> 00:01:09.740 Right. 11 00:01:09.740 --> 00:01:23.540 So apologies for the sound. And I still haven't actually changed it. Let me just do that now. OK. Now I'm going to start clipping and... let's see what that does. That looks... that looks better. No, maybe I am clipping now. I got excited. All right. 12 00:01:23.540 --> 00:01:32.690 This, my... this, dear listener, is going to be a heavily not edited at all podcast because Ben and I just need to record something so that you've got something to listen to. 13 00:01:32.690 --> 00:01:33.100 Yeah. 14 00:01:33.100 --> 00:02:02.800 Yeah. I met a number of people claiming to be our single listener at a conference recently, which was lovely. So shout out to the many single listeners that we had there. That was good to hear. It's always nice to get feedback. I mean, like, it's a funny thing that we do, right? We just chat, talk to each other. Apparently people listen to this, which is on them, in fairness. They don't have to. We're not making them. 15 00:02:02.800 --> 00:02:02.830 Okay. 16 00:02:02.830 --> 00:02:03.060 Yeah. Yeah. 17 00:02:03.060 --> 00:02:05.560 It's amazing. I don't understand it. 18 00:02:05.560 --> 00:02:17.950 So here we are. Yeah, we have no idea, as is normal, as is usual. But I've been doing some cool things that I would have just talked to you about because normally we would do this down the pub. 19 00:02:17.950 --> 00:02:18.050 Right. 20 00:02:18.050 --> 00:02:18.160 Yeah. 21 00:02:18.160 --> 00:02:19.820 But again, due to 4,000 miles between us, this is... 22 00:02:19.820 --> 00:02:27.520 Yeah. I haven't actually heard about any of this stuff, so it's not going to be... Yeah, I'm genuinely interested because I have not talked to you in a long time. 23 00:02:27.520 --> 00:02:28.160 the first time. So you know that I... 24 00:02:28.160 --> 00:02:33.700 Due to the aforementioned time dilation created by you going across the Atlantic Ocean that is stretched out. 25 00:02:33.700 --> 00:02:34.480 Is that what it is? 26 00:02:34.480 --> 00:02:35.720 Yes. 27 00:02:35.720 --> 00:02:43.700 That... it does make me wonder, because it does feel like we're in like the 1950s here in the UK, because they haven't got air conditioning and it is very, very, very hot. 28 00:02:43.700 --> 00:02:43.980 Uh-huh. 29 00:02:43.980 --> 00:02:45.100 Right. Right. That's... 30 00:02:45.100 --> 00:02:46.420 Someone should tell them about this new technology. 31 00:02:46.420 --> 00:02:47.700 Yeah. 32 00:02:47.700 --> 00:03:00.160 Oh, and they will not let me back in the country. Yeah. So one of the things that I got really excited about, well, you know, I love emulators. That's my thing. When I'm not forcing compilers to do things they shouldn't do, I am... 33 00:03:00.160 --> 00:03:08.930 emulating my childhood. And the thing that has really annoyed me all the time is that monitors are too crisp. 34 00:03:08.930 --> 00:03:09.710 Yep. 35 00:03:09.710 --> 00:03:10.500 Yep. 36 00:03:10.500 --> 00:03:23.800 I mean, we've talked about this before in a podcast, but like, you know, my very first computer, the first computer I programmed on was plugged into a portable color television, you know, full CRT bulbous screen, 37 00:03:23.800 --> 00:03:24.110 Yeah. 38 00:03:24.110 --> 00:03:24.740 Yeah. Right. 39 00:03:24.740 --> 00:03:25.340 Right. 40 00:03:25.340 --> 00:03:35.580 like analog push buttons, like when radio buttons were actual, the buttons you had on radios with a physical mechanism, you press one and the others pop out, you know, right. 41 00:03:35.580 --> 00:03:36.120 Right, right, right. Yeah. 42 00:03:36.120 --> 00:03:46.780 And then behind that was a tiny little thing you would tune to get it to the right channel. And then your, so your computer that you plugged in had to pretend to be a TV station, right? 43 00:03:46.780 --> 00:03:47.620 Right. 44 00:03:47.620 --> 00:03:58.090 It would generate radio frequency of PAL or NTSC at some frequency. You tune it into channel 36 in the UK or channel... 45 00:03:58.090 --> 00:04:01.840 Yeah, it was like three or four, I think. Yeah, three or four, something like that. 46 00:04:01.840 --> 00:04:02.180 Yeah. In the US, right. 47 00:04:02.180 --> 00:04:02.860 Right. 48 00:04:02.860 --> 00:04:06.960 And the TV didn't know that it wasn't actually plugged into an aerial listening to something off the... 49 00:04:06.960 --> 00:04:07.980 Right. 50 00:04:07.980 --> 00:04:38.690 But what that meant was, you know, not only was the CRT... not a perfect device. It's a very, very analog device that involves phosphors and things that... don't instantly light up and instantly fade away, which is part of their charm. But the picture quality was rubbish because you had to squirt color information down a single line. And it wasn't even like you could use a digital encoding, because this stuff had to work on like 1950s 51 00:04:38.690 --> 00:04:41.520 analog components when color TV was invented. 52 00:04:41.520 --> 00:04:41.920 Right. 53 00:04:41.920 --> 00:04:50.810 It's like the worst of all worlds. But it's really, really nostalgic to see the terrible picture quality that came from it. 54 00:04:50.810 --> 00:04:58.480 Right. 55 00:04:58.480 --> 00:05:04.960 And people would use this, right? There were tricks you could do to make colors look more blended and in some cases to achieve extra effects on a real TV that you won't get on an emulator. 56 00:05:04.960 --> 00:05:05.970 Anyway, this was annoying me. 57 00:05:05.970 --> 00:05:07.160 Mm-hmm. 58 00:05:07.160 --> 00:05:42.300 So I thought, right, sod it. I'm going to learn how this stuff works and I'm going to make my emulator faithfully reproduce all of the things, warts and all. And so I did one pass of this and it's a... it's kind of a fudge. It's like, yeah, we need to blur it a little bit. We need to do some of these effects. But it was like, no, this is not a first principles simulation of what's going on. So I thought I'm going to go deep rather than start by like just synthesizing the picture quality and that kind of stuff. Why don't I learn how to do it? How do I learn to be a TV person? 59 00:05:42.300 --> 00:06:06.980 I want to take a real BBC Micro or Sega Master System. I'm going to plug it into my computer. I'm going to use a software defined radio, which lets me decode radio frequency signals into essentially a stream of ones and zeros that I can read fast. And then I'm going to software decode that thing back into a color picture. 60 00:06:06.980 --> 00:06:34.320 And that's going to teach me everything I know about how the heck this works. And then I'm going to look at each bit of the code and kind of go, which things are available... What parts of that could I have done using analog electronics back in the day? Which things are like DSP tricks that you would only have had in high-end televisions and stuff like that? And now I can actually pluggably make a TV and say, I want a 1990s era 61 00:06:34.320 --> 00:06:51.330 type display, or I want... no, I want the actual 1984 Thorn TV that I had in my bedroom, which I have a photograph of, and I found... and I've got the manuals for, and I'm going to try and find an actual real one so I can do some real sampling. But you know, that's... it's been a journey, my friend. What do you want to know? 62 00:06:51.330 --> 00:06:51.740 Wow. 63 00:06:51.740 --> 00:07:02.310 Wow. Well, so, okay. So just to clarify exactly what you're saying here is you didn't have enough emulator in your emulator. So you added another layer of emulation on top of your emulator. 64 00:07:02.310 --> 00:07:04.820 So you have two layers of emulation. 65 00:07:04.820 --> 00:07:14.950 In fairness, I haven't put this into the emulator yet. There's a version in the emulator, but this is purely learning about the decoding. What I hadn't registered really is there's kind of two parts to the whole thing. 66 00:07:14.950 --> 00:07:15.300 Yeah. 67 00:07:15.300 --> 00:07:25.160 One is the RGB that is actually being generated by the computer, right? There is obviously RGB at some point. 68 00:07:25.160 --> 00:07:25.740 Mm-hmm. 69 00:07:25.740 --> 00:07:31.760 With the exception of NESes, which is a whole other story, and we don't have time for that, but like there is RGB, and then it goes through encoding. 70 00:07:31.760 --> 00:07:31.760 Yeah. 71 00:07:31.760 --> 00:07:40.520 And then the BBC Micro's output encoding circuitry would differ from the ZX Spectrum's one, from the Sega Master System. 72 00:07:40.520 --> 00:07:52.300 I'm sure all of the systems would come up with their own compromises about what's cheap to do or appropriate to do, to generate the signal. Then they would go through RF modulation, which adds a whole other thing in. 73 00:07:52.300 --> 00:08:06.960 They may or may not mix in the audio, because the audio is in there as well. And then they would send it off to the TV, right? So there's stage one is how does the output stage generate the RF signal that's coming out. And then stage two is which type of TV have you plugged it into? 74 00:08:06.960 --> 00:08:18.560 Is it a modern one? Is it a cheap and nasty color TV? Is it one of those ones where, you know, effectively over time, the heat of your... this is what I had with my friend Richard, we would go around his house. 75 00:08:18.560 --> 00:08:30.260 And after a lot of programming, the screen would start getting worse and worse and start shimmering. And we realized that, oh, you'd have to retune the TV as everything had gotten hot. And so all these analog components had gone out of lock effectively. 76 00:08:30.260 --> 00:08:33.210 And there was no... so it's... 77 00:08:33.210 --> 00:08:34.080 Yeah. 78 00:08:34.080 --> 00:08:46.100 Honestly, it's an amazing thing. And yeah, there's just so many layers. I've learned so much about how SDRs work, about how fast you have to sample stuff. Essentially, it's like an ADC. 79 00:08:46.100 --> 00:08:49.280 So it's like a sampler, an audio sampler, right? 80 00:08:49.280 --> 00:08:50.180 Right. Yeah, yeah, yeah. 81 00:08:50.180 --> 00:08:55.740 But not running at 44 kilohertz or 64 kilohertz. It's running at 32 megahertz. 82 00:08:55.740 --> 00:09:24.320 So it's 32 million samples a second, which is not totally unreasonable. It's fine. But the RF that we're looking at is a signal that varies and wiggles around a frequency that's like 400 megahertz or 300, 200 megahertz or something like that. So there's a kind of an analog trick for bringing down the signal from that really high domain down to a lower domain that you could then sample. 83 00:09:24.320 --> 00:09:24.420 Right. 84 00:09:24.420 --> 00:09:25.140 And how musical are you, Ben? 85 00:09:25.140 --> 00:09:33.720 You know, not particularly. And it's also possible that our listener is also not. So, you know, over-explaining is probably a good thing here. 86 00:09:33.720 --> 00:09:47.320 Right, that's fair. But right, so have you ever, you know when something is slightly out of tune, if you heard two notes that were slightly out of tune, they were both trying to be the same pitch. 87 00:09:47.320 --> 00:09:54.120 And so like, an A is 440 hertz, right? And now... yeah, I can't tell it's an A, right? 88 00:09:54.120 --> 00:09:54.840 Okay, yeah. 89 00:09:54.840 --> 00:10:00.800 I haven't got perfect pitch. But if it's... and then I also... someone played a 441 hertz sound, 90 00:10:00.800 --> 00:10:01.260 Right. 91 00:10:01.260 --> 00:10:10.220 I wouldn't be able to hear the difference. But if you played the two together, there's that horrible wobbling, whoa, whoa, whoa, whoa kind of thing that happens when they grate against each other. 92 00:10:10.220 --> 00:10:10.300 Yeah. Yeah. 93 00:10:10.300 --> 00:10:16.580 It's a crunchy, horrible thing when something is nearly in tune, but it isn't in tune, right? 94 00:10:16.580 --> 00:10:17.980 Mm-hmm. Mm-hmm. 95 00:10:17.980 --> 00:10:27.900 That, the frequency of the whoa, whoa, whoa of the two, beating and grating against each other, is the difference of the two frequencies. 96 00:10:27.900 --> 00:10:32.490 So 440 and 441 would give you a once a second wobbling sound. 97 00:10:32.490 --> 00:10:32.820 Okay, yeah, that makes sense. 98 00:10:32.820 --> 00:10:33.920 Right, right. 99 00:10:33.920 --> 00:10:43.920 So the trick, and anyone who knows about this for real, who's like done electronic engineering or whatever, is like screaming at their speakers right now, this is not a trick. 100 00:10:43.920 --> 00:10:44.080 Mm-hmm. I know. 101 00:10:44.080 --> 00:10:59.670 This is like just how it's done. But like the trick to me is, what you do is you play the two frequencies... when you want to tune to, say, 200 megahertz, you generate a local 200 megahertz signal using just your own oscillator. 102 00:10:59.670 --> 00:11:00.320 Okay. 103 00:11:00.320 --> 00:11:23.840 And you play that again at the same time. You multiply them. You mix them together. You multiply them in this instance. But like, go with me in this, my music analogy, right? And the result is, yes, you hear both of those tunes, but they're so high-pitched and high-frequency that they're then beyond what you can sample with your sampler. But the difference between them, the wobbling around, is much lower frequency. It's the difference of their frequencies. 104 00:11:23.840 --> 00:11:24.830 Okay. 105 00:11:24.830 --> 00:11:42.180 And so now you get a signal that is around about plus or minus, you know, however wide the various frequencies might be. And so by playing a 200 megahertz tone and multiplying that with whatever noise is happening off the radio, 106 00:11:42.180 --> 00:11:42.700 Okay. 107 00:11:42.700 --> 00:11:55.520 I can then sample that at, say, 32 megasamples a second. And what I've got is essentially a plus or minus, sort of, Nyquist limit is half of that, 16 megahertz around the 200 megahertz window. 108 00:11:55.520 --> 00:12:01.300 So I can get from minus, because it's the same, you can't tell if it's one hertz above or one hertz below. 109 00:12:01.300 --> 00:12:01.840 Okay. 110 00:12:01.840 --> 00:12:14.000 They both beat at once a second. So you get both the signals that are from like 200 to 216 and down to 184, whatever that... Right. 111 00:12:14.000 --> 00:12:14.050 Okay. 112 00:12:14.050 --> 00:12:14.320 But, and that's the band. 113 00:12:14.320 --> 00:12:21.640 And this is all to like bring these frequencies down into a range where you can sample them at the rate that you're able to sample them with the hardware that you have? 114 00:12:21.640 --> 00:12:27.160 Exactly. Without getting all those sort of like pointless noise of like lower frequency things that you don't care about. 115 00:12:27.160 --> 00:12:28.020 Okay. 116 00:12:28.020 --> 00:12:40.520 And then there's some other tricks that you have to do because, you know, again, you can't discriminate between something that's one hertz higher from what's only one hertz lower. And there's a trick. Maybe we want... if we talk about every trick here, we're going to be here for three hours. 117 00:12:40.520 --> 00:12:40.540 So I'm... 118 00:12:40.540 --> 00:12:49.240 And then the thing that's melting my brain here is that it's like, you know, you talk about this with audio and I can kind of like think about it, but it's like, this is television, right? 119 00:12:49.240 --> 00:12:49.900 Correct. Yes. 120 00:12:49.900 --> 00:13:02.100 So it's like, you know, it's not just audio. In fact, it's not even primarily audio. It's the signal that you're using to, you know, bend this, you know, electron ray, whatever the heck it is. 121 00:13:02.100 --> 00:13:03.760 Electron beam that's flashing back and forth. 122 00:13:03.760 --> 00:13:03.760 That's... yeah. 123 00:13:03.760 --> 00:13:04.420 Exactly. 124 00:13:04.420 --> 00:13:04.680 Right. 125 00:13:04.680 --> 00:13:06.720 And again, and it all had to be done in analog. 126 00:13:06.720 --> 00:13:06.860 Right. 127 00:13:06.860 --> 00:13:18.360 So you know this first stage I just described, you could imagine some kind of magical thing that oscillates. You get it tuning. When you're tuning the television, what you're really doing is tuning that oscillator to a frequency... that there's more... 128 00:13:18.360 --> 00:13:31.720 There's a middle stage. There's an intermediate frequency and stuff like that. But like for the purposes of this conversation, you're tuning an oscillator. And then the difference between the oscillator you tuned and the signal that's just got, of course, every TV station mixed into it will... 129 00:13:31.720 --> 00:14:07.620 will give you, will center it around the thing that you care about. And then if you filter the stuff that's higher and lower frequency, now you've just got your TV tune. But yeah, now you've got like another layer of encoding. So think about it as encoding. Now you've probably talked about, and I'm going to say a word that you're going to say a different way to me. And I don't know if it's a me thing or a UK thing, US thing. So the not-RF signal that you would plug in, the yellow lead on your old consoles where you didn't have the audio in, you would have like three leads, you'd have left and right audio, which would be red and white. 130 00:14:07.620 --> 00:14:07.880 Yeah. 131 00:14:07.880 --> 00:14:08.140 Yeah. 132 00:14:08.140 --> 00:14:10.030 And then the yellow lead, which would be the video. 133 00:14:10.030 --> 00:14:10.440 Yeah. 134 00:14:10.440 --> 00:14:13.150 Well, that will be what kind of video? 135 00:14:13.150 --> 00:14:22.060 Oh, I don't know. RF video. I mean, but yeah, I always think of it as like, you've got component and comPOSite and... okay. 136 00:14:22.060 --> 00:14:26.630 COMposite is the word I was looking for there. Yes. So yes, I would say COMposite. 137 00:14:26.630 --> 00:14:27.210 Yeah. Oh, okay. 138 00:14:27.210 --> 00:14:37.370 I don't know if it's just a thing that I say. So, you know, our listener can have a think. But yes, so effectively there are like several layers of encoding. 139 00:14:37.370 --> 00:14:37.760 Yeah. 140 00:14:37.760 --> 00:14:47.820 The first thing is we're going to make something RF so we could transmit it over the... what, the waves, the airwaves, right? The composite is too low frequency and everyone would pick the same one. 141 00:14:47.820 --> 00:14:57.280 So obviously every channel has its own. But in there are two things, right? One is the composite video, which is itself composed of more things, which we'll get to. 142 00:14:57.280 --> 00:14:57.620 Mm-hmm. 143 00:14:57.620 --> 00:15:08.580 And then there's essentially like an FM radio signal that is the audio that is just on the edge of the video signal, either side of it, the way that it works out. And I'm a bit vague on this bit because I haven't got to that yet. 144 00:15:08.580 --> 00:15:18.780 But you can imagine, yeah, given the amount of spectrum that you're allowed to use, the bandwidth of radio range, you would kind of fiddle it around and say, okay, the FM lives in this part of it. 145 00:15:18.780 --> 00:15:18.800 Mm-hmm. 146 00:15:18.800 --> 00:15:50.940 And then the middle part is all this. And the much wider part, for what it's worth, is the TV signal, which is itself composed of several things, right? Red, green, blue, synchronization pulses, like this is the top of the screen. This is a new line, right? Now in our... you and me, these are packets. These are like binary encoding and you go like, how about the start frame, you know, whatever. But like, this is... it can't be the case, because we're talking analog era electronics. 147 00:15:50.940 --> 00:16:07.500 And so first of all, the first trick is that it's amplitude modulated onto the carrier. So there is the carrier, you know, the 200 megahertz that I mentioned before, is just a wiggling 200 megahertz signal. 148 00:16:07.500 --> 00:16:08.280 Yeah. Yeah. 149 00:16:08.280 --> 00:16:12.300 And we just turn the volume of that up and down like old AM radio, right? 150 00:16:12.300 --> 00:16:12.640 Yeah. Right. 151 00:16:12.640 --> 00:16:20.940 Forget frequency modulation. We're not modulating the frequency. But by flapping the amplitude up and down fast enough, we are actually using frequencies around it. 152 00:16:20.940 --> 00:16:21.280 Right. 153 00:16:21.280 --> 00:16:26.240 If you were to put it through a spectrum analyzer, you see that you get this bandwidth just because of the way it... 154 00:16:26.240 --> 00:16:36.630 OK, so just to reiterate some of this back to make sure I understand what's going on here. You've got, because it's television, you have this limited frequency in which you're allowed to use for your signal, right? 155 00:16:36.630 --> 00:16:36.710 Yeah. 156 00:16:36.710 --> 00:16:36.800 Yeah. 157 00:16:36.800 --> 00:16:37.320 Correct. 158 00:16:37.320 --> 00:16:50.280 You're going to slice off some of that for the audio. You're going to slice off some of that for, you know, both channels of the audio. You're going to slice off some of that for the video. And then within that frequency, you're actually encoding the signal in the amplitude of the waves in that frequency. 159 00:16:50.280 --> 00:16:53.390 Correct, by modulating the up and down of that. 160 00:16:53.390 --> 00:16:53.660 Have I got that right? 161 00:16:53.660 --> 00:16:54.430 Yeah, yeah. 162 00:16:54.430 --> 00:16:55.040 Yeah. OK. 163 00:16:55.040 --> 00:17:07.290 And so the way that it's done is that a black picture is the brightest. So it's inverted, right? So a totally black screen would be just the normal 164 00:17:07.290 --> 00:17:08.020 OK. 165 00:17:08.020 --> 00:17:15.300 full amplitude... the RF signal. 166 00:17:15.300 --> 00:17:15.660 Yeah. 167 00:17:15.660 --> 00:17:16.020 Right. 168 00:17:16.020 --> 00:17:24.200 And this is also true, incidentally... Yeah, no, sorry, I'm confusing myself here. Right, forget... Go ahead. 169 00:17:24.200 --> 00:17:27.040 Is that true for the audio, too? This seems counterintuitive. 170 00:17:27.040 --> 00:17:33.280 I don't... I don't think so. The audio is separate from this. At this point, we've left the audio behind. It's been filtered off. 171 00:17:33.280 --> 00:17:33.440 OK. 172 00:17:33.440 --> 00:17:36.340 It goes into audio circuitry, and I haven't looked at that too much. 173 00:17:36.340 --> 00:17:47.250 But yeah, we've got this amplitude modulated thing where we want to extract from that essentially a single continuous analog signal from this wiggling thing. 174 00:17:47.250 --> 00:17:47.400 Okay. 175 00:17:47.400 --> 00:17:47.700 Okay. Okay. 176 00:17:47.700 --> 00:17:59.280 And the way that we do that is we treat the... Actually, I'm not sure what the circuitry does at this point, but we're looking for the amplitude. So let's just ignore the fact that it's wiggling anymore and just say it's the amplitude of this. 177 00:17:59.280 --> 00:18:09.780 We've got a thing that comes out. And now the amplitude is inverted such that the darkest picture is bright, the loudest, and the brightest picture would be almost no signal. 178 00:18:09.780 --> 00:18:13.220 It never goes completely zero, because then you don't have anything to lock onto. 179 00:18:13.220 --> 00:18:13.520 Yeah. Yeah. 180 00:18:13.520 --> 00:18:39.320 But it's there. So we've got a range now. We've got a range of, say, voltages. And... It's unimportant that it's inverted, other than like the very dark signal is always there. So even if the picture's black, you can tune into the stupid thing and actually know that you've picked up a black picture, right? So from now on... quickly, early on, you invert it the other way around. So it looks sane to humans where, you know, bright is high and dark is low. Let's go with that, right? 181 00:18:39.320 --> 00:18:39.700 Yeah. 182 00:18:39.700 --> 00:18:42.520 You with me so far? Because, yeah... the first thing is we invert it. 183 00:18:42.520 --> 00:18:46.820 Yeah. Is this why television static is mostly white? 184 00:18:46.820 --> 00:18:51.880 It is... we'll get to that actually. That's good, hold that thought, my friend, because this is the cool bit, right? 185 00:18:51.880 --> 00:18:52.880 Okay. All right. All right. 186 00:18:52.880 --> 00:19:05.420 So yes, we've got this, let's just say goes between zero and one volt, right? Where white is... one volt is bright white and zero would be black, except what we're gonna do is we're gonna say, no, no, no. We need a way of signaling the synchronization pulses. 187 00:19:05.420 --> 00:19:22.680 We need to say, this is the beginning of the screen. And we need to say, this is the beginning of a line, because what's happening behind the scenes is that there is... we want to synchronize the electromagnets in the TV with this picture so that they start at the top of the screen, they slowly go down and more quickly, they flip from left to right. 188 00:19:22.680 --> 00:19:23.260 Mm-hmm. Mm-hmm. 189 00:19:23.260 --> 00:19:31.560 And we wanna make sure that everything's synchronized. Otherwise the picture rolls or it's diagonally skewed because the rows aren't aligned, right? 190 00:19:31.560 --> 00:19:32.040 Yeah. 191 00:19:32.040 --> 00:19:42.860 But we need a way of saying, this is a big... this is like, we sort of out of band. And so the out of band is lower than black. It's like we go... we say, right, black is actually gonna be 0.3 volts. 192 00:19:42.860 --> 00:20:17.360 And anything below 0.3 volts is like blacker than black, and it's actually a signal. It's like, a thing is happening. It's our sort of out-of-band signal, because we know also that while we're between lines and while we're pulling the beam from the bottom to the top, we actually don't want to paint anything to the screen. Otherwise, you'd start seeing splurge as the light... as the beam retraces its steps, right? And you get pictures being overwritten with crap. So we want it to be low and we might as well just say, well, when it goes really low, that's a signal to you. 193 00:20:17.360 --> 00:20:17.900 Okay. 194 00:20:17.900 --> 00:20:19.640 Good so far? 195 00:20:19.640 --> 00:20:27.800 So you said blacker than black, like the amplitude... as the amplitude decreases, that is our range of signal, right? 196 00:20:27.800 --> 00:20:33.790 Yes. So we've got effectively between like 0.3 and one volt is the normal black to white. 197 00:20:33.790 --> 00:20:35.040 Okay. 198 00:20:35.040 --> 00:20:39.200 And then below, we're already talking... yeah, sorry, I've already inverted it so that it makes sane. 199 00:20:39.200 --> 00:20:39.860 So you've... we've already talked about it being flipped at this point. Got it. 200 00:20:39.860 --> 00:20:40.890 Yeah, yeah, yeah, yeah. 201 00:20:40.890 --> 00:20:40.990 Yeah, yeah, yeah, yeah. 202 00:20:40.990 --> 00:20:41.160 I'm sorry about that, yeah. 203 00:20:41.160 --> 00:20:42.800 No, that makes sense. I'm back with you again. 204 00:20:42.800 --> 00:21:07.720 Okay, yeah, I did do a bait-and-switch, changed my sort of... there, because it's just easier to think of it the right way up, right, the way you would want to see it, right, the way that it actually gets transmitted when you're using a composite cable. Because effectively by the time we have taken it away from being this amplitude modulated signal to just a signal between zero and one volts and turned it the right way up so that it makes sense, where now that's what you would get out of your composite cable. 205 00:21:07.720 --> 00:21:08.610 Right, yes. Right, right. 206 00:21:08.610 --> 00:21:08.840 Yeah. 207 00:21:08.840 --> 00:21:09.280 Yeah. 208 00:21:09.280 --> 00:21:09.880 OK, got it. 209 00:21:09.880 --> 00:21:20.060 Right. So no audio, no weird wiggling, just pure something you could put into an oscilloscope directly and go, oh, I can see what that's doing, as opposed to just a mass of wiggly lines. 210 00:21:20.060 --> 00:21:20.560 Right. 211 00:21:20.560 --> 00:21:21.110 Yeah. Yeah. 212 00:21:21.110 --> 00:21:22.210 Right. And I forget... 213 00:21:22.210 --> 00:21:22.480 Right. 214 00:21:22.480 --> 00:21:27.100 So TVs used to be black and white. You probably remember this. 215 00:21:27.100 --> 00:21:30.500 I don't know. Actually, that's not true. I did actually own a black and white TV. 216 00:21:30.500 --> 00:21:35.540 You're younger than me. I never... I think we had one black and white TV, but it was in my nan's house. 217 00:21:35.540 --> 00:21:37.620 Yeah. We had a cheap one that was black and white. That was like an extra one. 218 00:21:37.620 --> 00:21:50.540 But yeah, so the trick is that whatever we do to get color into our signal had to be, back in the 40s and 50s, whenever it was color was, had to be backwards compatible in the worst possible way. 219 00:21:50.540 --> 00:21:50.540 Yeah. 220 00:21:50.540 --> 00:21:50.540 Mm-hmm. 221 00:21:50.540 --> 00:21:59.360 Like they couldn't squeeze three copies. They couldn't go, oh, this is now red and this is now green and this is blue, because your black and white TV would be like, well, it's just... I only show what red is, or something like that. 222 00:21:59.360 --> 00:21:59.550 Right, right. 223 00:21:59.550 --> 00:21:59.740 Yeah, yeah. 224 00:21:59.740 --> 00:22:18.270 So there was a trick here. Yeah. Oh, but I missed over the... Going below 0.3 volts is a signal to either pull the signal up to the top of the screen if it's a long period of time, or if it's a short burst below 0.3 volts, it pulls it back to the left. 225 00:22:18.270 --> 00:22:18.500 Mm-hmm. 226 00:22:18.500 --> 00:22:27.770 So there are like two independent circuits that are always running inside the TV, one of which is just a square, both of which are sawtoothed. 227 00:22:27.770 --> 00:22:29.660 Yeah. 228 00:22:29.660 --> 00:22:31.330 Sawtooths, excuse me, sawtooths. 229 00:22:31.330 --> 00:22:31.650 Mm-hmm. 230 00:22:31.650 --> 00:22:31.960 Yeah. 231 00:22:31.960 --> 00:22:46.730 And they're set to be, you know, just slightly longer than a frame and just slightly longer than a line, so that they will naturally just kind of go zero to left to right, left to right continuously, and top to bottom slower, but continuously. 232 00:22:46.730 --> 00:22:47.440 Mm-hmm. Mm-hmm. 233 00:22:47.440 --> 00:22:59.760 But the pulse going that low for a while is a signal to say, doesn't matter where you think you are, start dragging yourself to the top of the screen if you're the top to bottom, or left of the screen. 234 00:22:59.760 --> 00:23:07.180 So that also gives you a certain amount of slop, where... not AI slop for a change, slop where if, for example, your TV's 235 00:23:07.180 --> 00:23:07.180 Yeah. 236 00:23:07.180 --> 00:23:32.230 crystal oscillators, or they weren't even crystals, but the little oscillators that were doing these sawtooths, was slightly out of spec, then, you know, you just keep rewiring, pulling them back onto the right sort of thing. And if there was no signal at all, then they would sort of free run. And that's when you would see the picture rolling, for example. If there was enough to see where the picture was, but you didn't... the TV couldn't pick up that synchronization pulse anymore, then it would just free run. 237 00:23:32.230 --> 00:23:32.270 Yeah. 238 00:23:32.270 --> 00:23:32.320 Yeah. 239 00:23:32.320 --> 00:23:40.130 And so the whole picture would spin over and over again. And I realize I'm gesturing wildly with my hands, which doesn't help our listener at all. 240 00:23:40.130 --> 00:23:41.360 Yeah. Yeah. 241 00:23:41.360 --> 00:23:56.180 So without getting into too many of the specifics, both of those things cause the TV to reset the top bit and the left to right bit. The interesting thing for me for the first time about this was like realizing that that sawtooth from top to bottom is always running. 242 00:23:56.180 --> 00:24:06.760 You know, you and I think that the beam scans from left to right, then it goes down a bit and comes back again sort of diagonally, and then it scans the next row left to right. 243 00:24:06.760 --> 00:24:11.600 But it doesn't. It's doing... it's always a slightly diagonal line from left to right. 244 00:24:11.600 --> 00:24:11.880 Yeah. 245 00:24:11.880 --> 00:24:16.680 And then it's a much less diagonal angle from right to left, because it's much quicker going back than it is going across. 246 00:24:16.680 --> 00:24:17.060 Mm-hmm. 247 00:24:17.060 --> 00:24:23.970 And so you'd think that the whole picture would be slightly wonky because it's... and it is. 248 00:24:23.970 --> 00:24:24.160 Yeah. 249 00:24:24.160 --> 00:24:30.000 And so they just adjust the damn magnets to turn them by half a degree backwards so that it's all the right way around again. 250 00:24:30.000 --> 00:24:31.350 It's just, you know, beautiful. 251 00:24:31.350 --> 00:24:31.540 Oh... 252 00:24:31.540 --> 00:24:35.040 And I had to model that because I'm like, why is everything slightly off? 253 00:24:35.040 --> 00:24:35.540 Right. 254 00:24:35.540 --> 00:24:36.180 Oh, yeah. Yeah. 255 00:24:36.180 --> 00:24:54.780 Okay, so that's the retrace. So we were talking about black and white. So you could imagine now it's really, really easy. We have these two electromagnets that are being dragged... dragging the electron beam up and down, left and right. They're synchronized with the signal. And then the rest of it is just the brightness. 256 00:24:54.780 --> 00:25:07.980 And that's just how many electrons we squirt at the screen in the direction the beam is currently pointing. And there you go. You've got a black and white telly. You are done. Hooray, high fives all round. 257 00:25:07.980 --> 00:25:16.550 But now we want color. And so, you know, as a computer programmer, we would say, oh, V2, you know, or you sort of come up with something. 258 00:25:16.550 --> 00:25:16.740 Right. 259 00:25:16.740 --> 00:25:29.980 Well, we've got the red, the green, and blue, and three channels. And then somehow, oh, there's also a black and white version. But no, they had to come up with a really clever way of getting color into the signal. 260 00:25:29.980 --> 00:25:41.940 So the trick, and this is the great thing, the trick is take... we take the color information and we break it down into three components. 261 00:25:41.940 --> 00:25:51.930 Rather than red, green and blue, we pick brightness, which we already have, because that's what the black and white signal was. And then we have two chrominance signals. 262 00:25:51.930 --> 00:25:52.660 Mm-hmm. 263 00:25:52.660 --> 00:26:02.410 And you know if you've ever pulled up a color picker in any of your art packages, you've probably seen the ones where you've got HSV and you know you've got brightness and then two different other sliders. 264 00:26:02.410 --> 00:26:02.550 Mm-hmm. 265 00:26:02.550 --> 00:26:02.700 Mm-hmm. 266 00:26:02.700 --> 00:26:15.780 And you can pick any color with three things. That's the beauty of like any space is that if it's a 3D space, you can have any coordinate system and you can get to all the points of the coordinate system as long as you've got three of them. 267 00:26:15.780 --> 00:26:28.580 And that's what it is. So like we have essentially a brightness, which is overall how bright something is. We have how saturated a color is, between totally that color or white, 268 00:26:28.580 --> 00:26:40.280 white, however white the brightness would let us go. And then we have a kind of color wheel for the third axis, which says, well, which color, if we're not white, which color are we tending towards? 269 00:26:40.280 --> 00:26:51.520 And you could imagine you're just, you know, just a genuine, honest kind of color wheel and like, well, it's a direction on there. And so now we've got three signals again. So that's cool. And one of them is one we're already transmitting. 270 00:26:51.520 --> 00:26:59.980 So can we hide the other two signals somewhere that a black and white telly that hasn't even... doesn't even know the color exists 271 00:26:59.980 --> 00:27:01.060 Right. 272 00:27:01.060 --> 00:27:08.350 doesn't see them, without using more bandwidth, because we can't add... you know, we've got all these TV channels packed into the RF spectrum. 273 00:27:08.350 --> 00:27:08.720 Yeah. 274 00:27:08.720 --> 00:27:29.060 And although we're talking... I'm talking about the composite part now, the width of that signal has to somehow be squished into the radio spectrum. So what we do is we observe that if we wiggle the brightness really fast and not that much, maybe the black and white TV won't notice it. 275 00:27:29.060 --> 00:27:29.480 Mm-hmm. 276 00:27:29.480 --> 00:27:45.150 Because it's a crap old piece of analog electronics, it's old anyway, a higher frequency wiggle in the brightness would probably go unnoticed, or at worst just makes the white areas look a little stippled in places where it's just varying quite quickly. 277 00:27:45.150 --> 00:27:45.780 Mm-hmm. 278 00:27:45.780 --> 00:27:57.060 Okay, but now we've got a wiggle. What do we do with this wiggle? Well, this wiggle, we can somehow encode two pieces of information with that wiggle. 279 00:27:57.060 --> 00:28:02.080 The amplitude of that wiggle could be one of the other dimensions. 280 00:28:02.080 --> 00:28:04.560 Oh, OK. Yeah, and the frequency is the other one? 281 00:28:04.560 --> 00:28:08.480 So now we've got one of them, but how do we get the third one? 282 00:28:08.480 --> 00:28:10.700 Yeah. Is it the frequency of the wiggle? 283 00:28:10.700 --> 00:28:12.500 What else... what's that, sorry? 284 00:28:12.500 --> 00:28:14.740 Is it the frequency of the wiggle? 285 00:28:14.740 --> 00:28:25.950 It's not the frequency... that would make sense at some level. And I think SECAM, the French thing, used something akin to that. But that would be too easy. 286 00:28:25.950 --> 00:28:26.520 OK. 287 00:28:26.520 --> 00:28:40.760 Also, there are limitations on what frequencies we can use for a variety of reasons, to do with the fact it has to not be a frequency that's going to interfere with this signaling itself, because all these other components are going. 288 00:28:40.760 --> 00:28:50.360 And also the RF... sorry, the audio is in there as well. So there was some careful picking of these numbers so they all don't divide into each other and you end up with like stripes or things like that. 289 00:28:50.360 --> 00:28:50.540 Okay. 290 00:28:50.540 --> 00:29:02.320 Because there are artifacts, which is partly why we're talking about this, because it... those are artifacts I'm trying to capture in the emulator. So the other thing that we can fiddle around that isn't the frequency is the phase. 291 00:29:02.320 --> 00:29:04.240 Oh, okay. Yeah. 292 00:29:04.240 --> 00:29:10.890 So you can slide that back and forth and have the peak at this point in time or push it back a little bit, and now we've got another dimension. 293 00:29:10.890 --> 00:29:11.240 Right. 294 00:29:11.240 --> 00:29:25.740 And so the phase, as you'll recall, can be measured as between 0 and 360 degrees, if you want to think about it, right, as a sine wave. You can like slide the sine wave back and forth. And that maps nicely into our 360 degree color wheel that we had. 295 00:29:25.740 --> 00:29:29.610 So that's how we pick the color. The color is just the phase of that wiggle. 296 00:29:29.610 --> 00:29:29.840 Okay. 297 00:29:29.840 --> 00:29:45.350 And then how saturated it is, is how wiggly... the brightness of that wiggle. So heavily saturated colors on a black and white television do have a grainy texture over the top of them now, because you can see the wiggle in it if you look hard. 298 00:29:45.350 --> 00:29:46.060 Mm-hmm. 299 00:29:46.060 --> 00:30:01.830 So that's cool. We have smuggled two pieces of extra information into our channel. Black and white TV people don't really notice it. But we've now got a new problem, which is that analog electronics is not very good at measuring things like phase differences. 300 00:30:01.830 --> 00:30:10.940 Because how accurate do you have to be with your signal to know if it's in or out of phase? And in and out of phase with what? 301 00:30:10.940 --> 00:30:11.900 Right. 302 00:30:11.900 --> 00:30:15.560 Maybe you need a PTP timestamp synchronization and now everyone's on the same page. 303 00:30:15.560 --> 00:30:15.560 Maybe. 304 00:30:15.560 --> 00:30:23.400 You're down to the... No, no, we haven't got any of that. It's got to work with crap electronics in a 1960s box. 305 00:30:23.400 --> 00:30:24.120 Yeah. 306 00:30:24.120 --> 00:30:25.840 Can I... can I take a guess? 307 00:30:25.840 --> 00:30:28.370 So we need... Yeah, please. This would be great, because I've been just jabbering. 308 00:30:28.370 --> 00:30:28.820 Can I... can I guess? 309 00:30:28.820 --> 00:30:30.620 So tell me, what do you think? 310 00:30:30.620 --> 00:30:36.960 So there's two checkpoints that you have. One is the screen reset and one is the line reset. 311 00:30:36.960 --> 00:30:38.000 Yes, go on. 312 00:30:38.000 --> 00:30:43.040 So it could be either of those, or maybe even both. 313 00:30:43.040 --> 00:30:49.700 You are bang on the money, my friend. And it almost makes me think you're cheating and Googling, but I can see your hands, so I know you aren't. Yeah. 314 00:30:49.700 --> 00:30:51.840 I am not. I am not. 315 00:30:51.840 --> 00:31:01.330 So at the beginning of each line, after we've had the little dip below the 0.3 volts that says, hey, this is the beginning of the line. 316 00:31:01.330 --> 00:31:01.740 Mm-hmm. 317 00:31:01.740 --> 00:31:10.030 And so we know that the electron beam has been dragged back and is currently now way off the left-hand side of the screen. 318 00:31:10.030 --> 00:31:10.480 Mm-hmm. 319 00:31:10.480 --> 00:31:16.730 We then come up to like a black level, because we're in the sort of border on the left-hand side. 320 00:31:16.730 --> 00:31:17.020 Right. 321 00:31:17.020 --> 00:31:20.990 And just before then, and there's something like... there's the front porch and the back porch. 322 00:31:20.990 --> 00:31:21.160 Right. 323 00:31:21.160 --> 00:31:25.400 There's some stupid names for these things, which is, you know, stupid, hilariously funny. 324 00:31:25.400 --> 00:31:25.660 Interesting. Yeah. 325 00:31:25.660 --> 00:31:37.100 We just do a quick burst of that color signal, just a little of it, that's short enough that, again, it's not going to be visible. It's off the side of the screen. 326 00:31:37.100 --> 00:31:45.540 But anything that's looking for it will see it and go, ah, two things. One, this is a color TV signal. It's not a black and white TV signal. 327 00:31:45.540 --> 00:31:45.620 Right. 328 00:31:45.620 --> 00:31:54.580 It's a color TV signal, because I've seen the color burst. Two, synchronize my very short-lived one-line's worth signal 329 00:31:54.580 --> 00:31:55.140 Right. 330 00:31:55.140 --> 00:32:16.360 local oscillator of this color frequency, so that I've now got a reference that I can compare everything else to, and I can compare it to see if it's in or out of phase and by how much. And so that is the trick of getting color. Now decoding that is a pain, but you mentioned something about the black, you know, static. 331 00:32:16.360 --> 00:32:18.470 So do you think you can answer your own question now? 332 00:32:18.470 --> 00:32:18.620 Yeah. 333 00:32:18.620 --> 00:32:20.620 Why is it black and white? 334 00:32:20.620 --> 00:32:27.980 Well, because it's not going to have that burst right at the right time to tell it that it's a color TV. 335 00:32:27.980 --> 00:32:34.370 Bingo. Bingo. So the color TV set will... will assume it's a black and white picture, because it can't synchronize to it and it can't find the color burst. 336 00:32:34.370 --> 00:32:34.630 Yeah. 337 00:32:34.630 --> 00:32:34.880 Yeah. 338 00:32:34.880 --> 00:32:42.880 And so it will suppress all of its own color decoding circuitry. And so the noise only comes out in black and white. Congratulations, sir. 339 00:32:42.880 --> 00:32:43.520 Wow. 340 00:32:43.520 --> 00:32:45.000 You've won today's podcast. 341 00:32:45.000 --> 00:32:50.330 Well, I just want to thank everyone involved, you know, my friends, my family here to support me. 342 00:32:50.330 --> 00:32:50.420 Yeah. 343 00:32:50.420 --> 00:32:57.160 And I'm just really proud of this accomplishment today. So thank you. Thank you all. Really appreciate it. 344 00:32:57.160 --> 00:33:18.890 But so I guess, you know, and so emulating and simulating this has been an absolute blast, and learning all of the various things that they do to the TVs that do that, like, period appropriate. And I learned, for example, that there are delay lines for something we'll hopefully talk about in a second, which required a piece of glass that's exactly the right size so that like essentially it puts... 345 00:33:18.890 --> 00:33:19.180 Wow. 346 00:33:19.180 --> 00:33:31.700 There's like a piezoelectric crystal on both sides of this bit of glass, and it knows it takes 64 microseconds for the vibrations to make it through to the other side. And that's how you get a delay line, an analog delay line, for 64 micros. 347 00:33:31.700 --> 00:33:32.700 You're like, what? 348 00:33:32.700 --> 00:33:33.140 Wow. 349 00:33:33.140 --> 00:33:46.840 There are other things that use specially shaped piezo crystals that then can filter out frequencies. It's just so clever. But while we're here, and as we've just been talking about the color burst in particular, 350 00:33:46.840 --> 00:33:48.720 This sounds like an amazing project. Yeah. Yeah. 351 00:33:48.720 --> 00:33:56.380 What is the name of the European, or most of the European, TV standard? 352 00:33:56.380 --> 00:33:57.840 PAL. 353 00:33:57.840 --> 00:33:59.760 Do you know what PAL stands for? 354 00:33:59.760 --> 00:34:02.840 Oh, I do not. 355 00:34:02.840 --> 00:34:21.400 It stands for phase alternating lines. And I think that probably tells you something about what happens on each line. And maybe about the color part, because this is where NTSC, which is something like the North American Television Standards Committee or something like that, which was developed first, incidentally. 356 00:34:21.400 --> 00:34:21.710 Phase alternating lines. 357 00:34:21.710 --> 00:34:22.020 Yeah, yeah. Uh-huh. 358 00:34:22.020 --> 00:34:33.440 So NTSC predates PAL by about a decade or so. And so PAL learned from NTSC and went, we like everything about this, but... there's this one thing, and they fixed something. 359 00:34:33.440 --> 00:34:33.540 Yeah. 360 00:34:33.540 --> 00:34:36.500 And one thing, so phase alternating lines. 361 00:34:36.500 --> 00:34:36.900 Uh-huh. 362 00:34:36.900 --> 00:34:49.260 So if we're using phase to control color, the hue, right, then my guess here is that we shift the phase every other line. 363 00:34:49.260 --> 00:34:49.860 Okay. 364 00:34:49.860 --> 00:34:57.520 I'm trying to think of why that helps, though. I don't know why that helps. 365 00:34:57.520 --> 00:35:02.120 Exactly. Yeah. Well, let's talk briefly, because I've looked... we're at 35 minutes, gosh. 366 00:35:02.120 --> 00:35:02.500 Why does that help? 367 00:35:02.500 --> 00:35:02.600 Right. 368 00:35:02.600 --> 00:35:17.820 Let's talk briefly about one of the problems that NTSC had. And actually, this would be interesting, because I didn't grow up with an NTSC set. I grew up cursing them in the 90s, because we had to like try and make our graphics look good on NTSC TVs for like games. 369 00:35:17.820 --> 00:35:32.830 But they wouldn't have suffered from the problem I'm about to describe. So... The problem with the phase being the color information is that tiny, tiny errors start moving you around on that color wheel, right? 370 00:35:32.830 --> 00:35:32.920 Mm-hmm. Mm-hmm. 371 00:35:32.920 --> 00:35:45.800 If you're just out by one degree, you're moving around this color wheel. And so you had a... you may have had an extra control on your early analog TVs that I would not have had. 372 00:35:45.800 --> 00:35:54.860 I had color, brightness, contrast. Those were the three things. Do you remember another one? I'm really... you're younger than me, so you probably don't. 373 00:35:54.860 --> 00:35:56.980 You know, I don't remember. 374 00:35:56.980 --> 00:35:57.370 It's been a while. 375 00:35:57.370 --> 00:35:57.800 It's been a bit. 376 00:35:57.800 --> 00:36:05.440 So my understanding is that earlier American sets would have a tint as well. 377 00:36:05.440 --> 00:36:08.460 Oh, yeah. Yes. 100%. Mm-hmm. 378 00:36:08.460 --> 00:36:38.420 And so you would fiddle with the tint, because people's skin color would look like orangey or greeny or whatever sometimes, because... now you probably know where I'm going with this... because of small errors in the phase. Those errors commonly come from the signal being reflected off a building near you. And if you take two signals that are identical and add them together with just a tiny delay in one of them, it's similar to shifting the phase of everything. 379 00:36:38.420 --> 00:36:39.060 Oh, yeah. 380 00:36:39.060 --> 00:36:43.260 And I'm going to wave my hands a lot here, because I've read the math a few times and it hasn't really gone in. 381 00:36:43.260 --> 00:36:43.560 OK. 382 00:36:43.560 --> 00:37:00.240 But there's sort of an unfortunate thing, either if the TV is just not good at locking onto that signal and the parts aren't great, or if there's a systematic error because everything's being slightly delayed and you're getting a mirror copy coming in, then the colors would morph, and it would depend on where the TV set is. 383 00:37:00.240 --> 00:37:00.500 Right. 384 00:37:00.500 --> 00:37:16.640 And it depends on like how warm things are. And you... so fiddle around with this tint. So this is the thing the Germans who came up with PAL was like, how can we fix this? And they made the observation, which to this day lives on in things like JPEG. 385 00:37:16.640 --> 00:37:22.400 So, and that is, humans care about the brightness far more than they care about the color. 386 00:37:22.400 --> 00:37:22.400 Okay. 387 00:37:22.400 --> 00:37:22.400 Right. So, you know, in, say, a JPEG, we store the... the brightness information at a higher resolution than we store the color information, because then you tend not to notice. 388 00:37:22.400 --> 00:37:22.400 Okay. Yeah. 389 00:37:22.400 --> 00:37:22.400 Yeah. Yeah. 390 00:37:22.400 --> 00:37:38.960 This trick comes from this area. 391 00:37:38.960 --> 00:37:39.040 Right. 392 00:37:39.040 --> 00:38:11.200 So they said, well, what if it didn't really matter if we were storing color on every line, unique color in every line? And so it's not... it's not actually that they changed it. But what they said was like, if we flip the phase every other line and we delay the previous line's color and add it to the current line's color, we cancel out any phase error between the two of them, because they've been affected by 180 degrees different in each direction. 393 00:38:11.200 --> 00:38:23.400 And every time I say that out loud, I go, there seems like there's something wrong with that. But I sit down, I do the maths, and the phase error cancels out. But at the loss of like the fact that you are mixing together two lines' worth of color information to kind of get one blurrier line of color information. 394 00:38:23.400 --> 00:38:23.400 Of course it was the Germans. 395 00:38:23.400 --> 00:38:53.700 So that is the... and again, probably without a picture or even, again, without me being very confident about it, but that phase alternation and knowing that the TV is going to do obviously the reverse, any error, any fixed error that you've added in cancels out, because when you reverse it the second time, you're adding minus... if you're bouncing off a building, it's adding three degrees of error. 396 00:38:53.700 --> 00:38:54.200 Yeah. 397 00:38:54.200 --> 00:39:00.530 You add in three degrees of error on the first line. You subtract three degrees of error on the second line. You assume that the other part is the same. 398 00:39:00.530 --> 00:39:00.780 Yeah. 399 00:39:00.780 --> 00:39:05.690 And so those two cancel out. You divide by two and you get just the right phase out of it. 400 00:39:05.690 --> 00:39:05.840 Yeah. 401 00:39:05.840 --> 00:39:06.460