1 00:00:00,049 --> 00:00:05,060 If you were born some time after, oh, let’s say 1988, then when you see this symbol, the 2 00:00:05,060 --> 00:00:10,260 Dolby logo, you probably think of a movie theater or DVD with Dolby Digital 7.1 surround 3 00:00:10,260 --> 00:00:14,519 sound, or perhaps Dolby’s newer technologies such as Atmos or Dolby Vision HDR. 4 00:00:14,519 --> 00:00:18,480 So you might be a little surprised to see it on an old cassette tape. 5 00:00:18,480 --> 00:00:19,920 What’s it doing there? 6 00:00:19,920 --> 00:00:21,919 Well, Dolby didn’t start out in the movie business. 7 00:00:21,919 --> 00:00:25,899 In fact, they started in the business of sound. 8 00:00:25,899 --> 00:00:30,449 I suppose that’s not a surprise, after all that’s pretty much exactly what they do 9 00:00:30,449 --> 00:00:34,280 today, but their first product had nothing to do with surround sound, movies, or anything 10 00:00:34,280 --> 00:00:36,010 high-tech like that. 11 00:00:36,010 --> 00:00:38,670 Their first product was Dolby Noise Reduction. 12 00:00:38,670 --> 00:00:44,219 Ray Dolby started the company in 1965, and their first product was the Dolby 301 unit, 13 00:00:44,219 --> 00:00:47,289 a machine designed to help eliminate tape noise. 14 00:00:47,289 --> 00:00:51,500 With magnetic tape, the random structure of the particles that make up the tape create 15 00:00:51,500 --> 00:00:56,030 an audible signal that we don’t want, a quiet but still noticeable noise that sounds 16 00:00:56,030 --> 00:00:57,310 like a hiss. 17 00:00:57,310 --> 00:01:00,800 This noise is always there, again due to the structure of the tape itself. 18 00:01:00,800 --> 00:01:04,560 During loud sections of a recording, it’s not that noticeable because compared the the 19 00:01:04,560 --> 00:01:06,500 signal, it’s barely perceptible. 20 00:01:06,500 --> 00:01:10,380 But during quiet parts of a song, it becomes much more of a problem. 21 00:01:10,380 --> 00:01:13,680 Through the magic of video editing, I’m going to take the audio from this video and 22 00:01:13,680 --> 00:01:16,740 slap it on a cassette so you hear what this noise sounds like. 23 00:01:17,740 --> 00:01:18,740 There. 24 00:01:18,740 --> 00:01:19,740 That’s, better? 25 00:01:19,740 --> 00:01:22,930 Well I suppose it’s actually worse, but there you go, that’s the problem. 26 00:01:22,930 --> 00:01:27,690 This tape noise permeates all recordings, and particularly in quiet or silent portions, 27 00:01:27,690 --> 00:01:29,450 it’s quite noticeable. 28 00:01:29,450 --> 00:01:32,000 Ray Dolby wanted to figure out a way to get rid of it. 29 00:01:32,000 --> 00:01:33,650 His solution is quite elegant. 30 00:01:33,650 --> 00:01:36,830 First, let me turn on Dolby Noise Reduction so you can hear the difference. 31 00:01:37,830 --> 00:01:38,880 There, that is better. 32 00:01:38,880 --> 00:01:40,540 Now the noise is much less noticeable. 33 00:01:40,540 --> 00:01:43,750 It’s still there, sure, but it’s definitely not as annoying. 34 00:01:43,750 --> 00:01:47,430 But what’s most interesting is the fact that the actual signal we wanted is unaffected. 35 00:01:47,430 --> 00:01:51,190 I don’t sound any different now that we’re using noise reduction, the only thing that 36 00:01:51,190 --> 00:01:54,680 happened is now you can hear me better because the noise has gone away. 37 00:01:54,680 --> 00:01:55,830 So how does this work? 38 00:01:55,830 --> 00:01:59,660 Well, the first thing Dolby did was to figure out what the tape noise was. 39 00:01:59,660 --> 00:02:04,410 By using spectral analysis of a blank tape, you can see what sound frequencies make up 40 00:02:04,410 --> 00:02:05,410 the noise. 41 00:02:05,410 --> 00:02:08,090 Therefore, you can get a noise profile. 42 00:02:08,090 --> 00:02:11,900 Once Dolby had figured out the particular frequencies that made up the sound, it was 43 00:02:11,900 --> 00:02:14,730 simply a matter of using an equalizer to tune out those frequencies. 44 00:02:14,730 --> 00:02:18,740 You’ve probably used an equalizer before as they come built into many music playing 45 00:02:18,740 --> 00:02:21,620 applications such as iTunes and the like. 46 00:02:21,620 --> 00:02:25,780 The equalizer has a slider for particular ranges of sound frequencies, and you can either 47 00:02:25,780 --> 00:02:28,260 boost each band or suppress it. 48 00:02:28,260 --> 00:02:32,030 Dolby noise reduction is a lot like taking the frequencies that make up noise and tuning 49 00:02:32,030 --> 00:02:34,650 them down a lot to make the noise quieter. 50 00:02:34,650 --> 00:02:36,150 OK, so let’s do that. 51 00:02:36,150 --> 00:02:40,690 (pause) Now the noise is a lot less noticeable, But we have a new problem. 52 00:02:40,690 --> 00:02:44,790 Now the sound we want is dull, and my voice sounds muffled. 53 00:02:44,790 --> 00:02:48,000 This isn’t really any better, it’s just a different problem. 54 00:02:48,000 --> 00:02:50,520 So how come nothing changed when we used it the first time? 55 00:02:50,520 --> 00:02:52,590 Let me turn that back off. 56 00:02:52,590 --> 00:02:57,090 Nothing changed the first time because Dolby Noise Reduction is actually a two way process. 57 00:02:57,090 --> 00:03:02,450 In order for it to work, the recording also has to be processed with Dolby NR. 58 00:03:02,450 --> 00:03:05,990 During recording, the Dolby Chip inside the cassette deck actually does the opposite of 59 00:03:05,990 --> 00:03:07,910 what it does during playback. 60 00:03:07,910 --> 00:03:12,020 Instead of cutting the frequencies associated with noise, it boosts them. 61 00:03:12,020 --> 00:03:15,420 Now I’ll turn on Dolby noise reduction at the time of recording, but I’ll play the 62 00:03:15,420 --> 00:03:17,270 tape back without Dolby turned on. 63 00:03:17,270 --> 00:03:18,270 (pause) 64 00:03:18,270 --> 00:03:22,730 Now my voice sounds really harsh, with ess sounds being particularly annoying. 65 00:03:22,730 --> 00:03:28,260 The ess sound is so satisfactorily nasty such that some sadistic, senseless sad sack might 66 00:03:28,260 --> 00:03:32,470 succumb to the sickening task of overusing these sounds to facilitate the driving of 67 00:03:32,470 --> 00:03:33,680 a point home. 68 00:03:33,680 --> 00:03:36,220 (clears throat) Yes, but there is a reason for this. 69 00:03:36,220 --> 00:03:39,990 By over-boosting these frequencies during recording, we eliminate the problem of a dull 70 00:03:39,990 --> 00:03:41,690 recording when using noise reduction. 71 00:03:41,690 --> 00:03:44,020 Let’s look at the equalizer again. 72 00:03:44,020 --> 00:03:46,910 This is what happens when we use dolby during playback. 73 00:03:46,910 --> 00:03:49,660 These frequencies are pulled down to kill the noise. 74 00:03:49,660 --> 00:03:53,930 But by doing this, we also pull down any components of the signal , that is the sounds that we 75 00:03:53,930 --> 00:03:55,599 want, that lie within that range. 76 00:03:55,599 --> 00:03:59,790 But if you boost the frequencies that lie in the spectrum with the noise while recording, 77 00:03:59,790 --> 00:04:04,020 you end up with a recording that has these particular frequencies recorded too loud. 78 00:04:04,020 --> 00:04:08,400 Then, when you pull those frequencies down during playback, you not only pull the noise 79 00:04:08,400 --> 00:04:12,680 down and make it quieter, but you also bring the boosted parts of the signal down back 80 00:04:12,680 --> 00:04:13,880 to where they should be. 81 00:04:13,880 --> 00:04:18,579 In essence, the boosting of sounds we want during recording is canceled out bringing 82 00:04:18,579 --> 00:04:21,109 them back to normal during playback. 83 00:04:21,109 --> 00:04:24,300 Because any components of the signal that lie within the noise profile are boosted to 84 00:04:24,300 --> 00:04:28,849 compensate for the noise reduction, the effect is that only the noise is reduced. 85 00:04:28,849 --> 00:04:30,759 The signal remains intact. 86 00:04:30,759 --> 00:04:32,860 This is a process known as companding. 87 00:04:32,860 --> 00:04:36,860 The dynamic range of the recording, that is the difference between loud and soft sounds, 88 00:04:36,860 --> 00:04:40,550 it compressed during recording because some frequencies are recorded louder than they 89 00:04:40,550 --> 00:04:41,949 should be. 90 00:04:41,949 --> 00:04:46,330 Then during playback, the dynamic range is expanded by lowering those frequencies, and 91 00:04:46,330 --> 00:04:47,840 thus the noise floor. 92 00:04:47,840 --> 00:04:49,309 There is a catch, though. 93 00:04:49,309 --> 00:04:53,430 Because some sounds are boosted by the dolby circuitry when recording, the record levels 94 00:04:53,430 --> 00:04:57,689 that you use must be reduced a little bit to ensure they don’t get distorted. 95 00:04:57,689 --> 00:05:02,199 That’s why the Dolby symbol usually appears on the level meter of a tape deck--this is 96 00:05:02,199 --> 00:05:06,150 the point on the meter that should not be exceeded when using noise reduction. 97 00:05:06,150 --> 00:05:09,479 When setting the level for recording, you’d want the meter to just barely touch it at 98 00:05:09,479 --> 00:05:10,750 the loudest sections. 99 00:05:10,750 --> 00:05:15,639 The Dolby system used on consumer machines like this wasn’t the best Dolby had to offer. 100 00:05:15,639 --> 00:05:19,789 Dolby A noise reduction is what Ray Dolby first invented, and was what was found in 101 00:05:19,789 --> 00:05:21,979 the professional recording studio. 102 00:05:21,979 --> 00:05:26,469 But Dolby-B, what’s used on the vast majority of cassettes, worked pretty well, and it was 103 00:05:26,469 --> 00:05:29,099 a lot simpler and thus cheaper to implement. 104 00:05:29,099 --> 00:05:34,159 Later consumer systems, such as Dolby C and Dolby S, further improved on the noise reduction 105 00:05:34,159 --> 00:05:35,159 process. 106 00:05:35,159 --> 00:05:40,300 Dolby C came about in 1980, and it worked very well, about 60 % better than B. The problem 107 00:05:40,300 --> 00:05:45,910 with Dolby C, however, was that on non-compatible equipment, the tape sounds really weird. 108 00:05:45,910 --> 00:05:46,910 Have a listen. 109 00:05:46,910 --> 00:06:14,809 Here’s a clip of some music from the YouTube Audio Library. 110 00:06:14,809 --> 00:06:25,389 Now here’s what it sounds like on a Dolby-C encoded tape, played back without Dolby circuitry. 111 00:06:25,389 --> 00:06:45,029 That’s messed up. 112 00:06:45,029 --> 00:06:48,309 Turning on Dolby B helped a little, but not much. 113 00:06:48,309 --> 00:06:52,389 Dolby C used a much more complicated process to reduce noise, and that’s why recordings 114 00:06:52,389 --> 00:06:54,029 made with it are less compatible. 115 00:06:54,029 --> 00:06:58,499 It also meant that pre-recorded tapes didn’t shift to Dolby C, since no one wants to buy 116 00:06:58,499 --> 00:07:02,119 music that doesn’t sound any good, and even fewer people were willing to put down the 117 00:07:02,119 --> 00:07:03,749 money for a new cassette deck. 118 00:07:03,749 --> 00:07:08,360 The next consumer development, Dolby S, was supposedly so good that with a decent quality 119 00:07:08,360 --> 00:07:12,389 Chromium tape, you couldn’t tell the difference between a cassette encoded with Dolby S and 120 00:07:12,389 --> 00:07:13,680 a CD. 121 00:07:13,680 --> 00:07:18,080 It also was more compatible with Dolby B equipment, not suffering from the distortion of dolby 122 00:07:18,080 --> 00:07:23,611 C. The problem with Dolby S, though, was that it came about far too late, in 1989, with 123 00:07:23,611 --> 00:07:26,409 the CD already having found a prominent place in the market. 124 00:07:26,409 --> 00:07:30,469 The best noise-reduction technologies, such as those used in the professional Dolby SR 125 00:07:30,469 --> 00:07:35,330 or the competing DBX system, used very aggressive companding. 126 00:07:35,330 --> 00:07:39,349 The idea is to keep the signal recorded on the tape loud relative to the noise at all 127 00:07:39,349 --> 00:07:40,349 times. 128 00:07:40,349 --> 00:07:44,159 Remember, in loud sections of the recording, the noise isn’t noticeable compared to the 129 00:07:44,159 --> 00:07:45,159 signal. 130 00:07:45,159 --> 00:07:49,639 So the best possible system would make the recording loud all the time, and during playback 131 00:07:49,639 --> 00:07:54,189 could tell which parts were intended to be quiet and thus lower the volume of the whole 132 00:07:54,189 --> 00:07:59,050 signal back to normal, therefore making the noise practically imperceptible. 133 00:07:59,050 --> 00:08:02,860 Though this isn’t quite how companding is accomplished in the best systems, the effect 134 00:08:02,860 --> 00:08:03,940 is similar. 135 00:08:03,940 --> 00:08:08,050 But the problem with using this technique is that listening to a DBX encoded tape without 136 00:08:08,050 --> 00:08:11,729 a DBX capable decoder is very unpleasant. 137 00:08:11,729 --> 00:08:13,099 The same goes for Dolby SR. 138 00:08:13,099 --> 00:08:17,409 And that’s precisely why the better systems never took off in the consumer space. 139 00:08:17,409 --> 00:08:21,879 Dolby B was simple and still pretty effective, but best of all a Dolby-B encoded tape could 140 00:08:21,879 --> 00:08:25,979 be played back on a standard cassette deck with reasonable results, again with the only 141 00:08:25,979 --> 00:08:29,389 difference being an over-emphasis of the treble sounds. 142 00:08:29,389 --> 00:08:33,039 And with most stereos having a bass and treble adjustment, just slightly turning down the 143 00:08:33,039 --> 00:08:36,839 treble would bring the sound back to more or less normal while still providing some 144 00:08:36,839 --> 00:08:41,199 noise reduction, of course the noise reduction you’d get would be less precise and effective. 145 00:08:41,199 --> 00:08:45,350 We don’t use noise reduction any more because, well, noise isn’t a problem any more. 146 00:08:45,350 --> 00:08:48,899 Now that we use digital sound in virtually all applications, there’s no need to add 147 00:08:48,899 --> 00:08:51,019 this sort of complex circuitry. 148 00:08:51,019 --> 00:08:53,630 But I’m still impressed by the elegant solution to the problem. 149 00:08:53,630 --> 00:08:58,209 Automatic pre-emphasis of sounds within the noise profile when recording and then de-emphasis 150 00:08:58,209 --> 00:09:03,210 when playing it back is so delightfully simple, effective, and logical, that I can’t help 151 00:09:03,210 --> 00:09:04,220 but admire it. 152 00:09:04,220 --> 00:09:05,490 Thanks for watching. 153 00:09:05,490 --> 00:09:10,560 If you like this sort of video, be sure to give it a thumbs up and subscribe to Technology 154 00:09:10,560 --> 00:09:11,560 Connections. 155 00:09:11,560 --> 00:09:14,579 I’m doing my best to keep videos like this coming your way. 156 00:09:14,579 --> 00:09:17,500 If you have ideas of what to explore next, leave them in the comments. 157 00:09:17,500 --> 00:09:18,500 I’d love to hear them. 158 00:09:18,500 --> 00:09:19,050 I’ll see you next time!