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How to pack a stereo signal in one record groove
- PopAlongKid 4y agoTrivia: well into the 1970s, promotional copies of hit songs were released to U.S. radio and record stores on vinyl 7-inch 45 RPM format, one side in mono, and one side in stereo.
- lqet 4y agoNow there is something Bartosz Ciechanowski should write a blog post about! I also think something important is missing from this explanation: the vertical/horizontal solution would not have been backwards compatible in two ways: (1) A mono needle would not have been able detect the vertical movement, resulting in a missing channel. (2) A stereo needle able to play such a record would not have been able to play a classic mono record, because the mono signal would have only been translated into a single channel (the left or right channel), and the other channel would have remained silent. (1) would've made stereo records unattractive for customers who already owned an existing mono player, and (2) would've made stereo players unattractive to customers who already had a substantial mono record collection. With the 45 degree solution, existing mono players were able to play stereo records (the horizontal movement is exactly the sum of the two channels), and stereo players were able to play existing mono records. For this to work, the left and right signals were recorded in opposite phase. A really elegant solution, which somehow reminds me of the cover of GEB [0]. PS: if you are interested in cutting-edge record groove technology, the "Füllschriftverfahren" invented by Eduard Rhein might interest you. It was an early compression technology for audio. The method was based on earlier work by the London-based Columbia Graphophone Company, but their work was never used in practice. Basically, before this invention, the spacing between the grooves on a record was fixed, with enough margins so that large amplitudes would not cut into neighboring grooves. Rhein build a machine that dynamically spaced the grooves based on the maximum local amplitude, allowing much smaller groove margins for quiet parts of an audio file, and therefore increased information density. This nearly doubled the running time of typical records. Sadly, I only found an extensive description of this technology in German, including original patents [1]. But the figures are self-explaining. [0] https://i.stack.imgur.com/OKBvZ.jpg https://i.stack.imgur.com/OKBvZ.jpg [1] https://grammophon-platten.de/page.php?530 https://grammophon-platten.de/page.php?530
- PopAlongKid 4y ago>For this to work, the left and right signals were recorded in opposite phase. I don't know, but found the following comment in an audiophile/collector forum, note the comment about phase. https://www.discogs.com/forum/thread/774378?message_id=7697060#7697060 https://www.discogs.com/forum/thread/774378?message_id=76970... "When Stereo records first appeared circa 1958, it was important that they were NOT played on existing mono equipment, as the two playback modes were incompatible with regards to wear and tear. A mono player would damage the stereo record primarily because a stereo record required the stylus to wiggle up and down as well as left and right. Mono only required left and right, and mono players of the time had little up and down capacity. "Mono record players (or more specifically cartridges and stylii) then incorporated the ability to play stereo records and modern, of the time (late 1960's) players could therefore play a stereo record without damage. At the same time mono records were phased out, so people needed to be assured they could still purchase records (which were only available in stereo) and play them without causing damage. "It has nothing to do with the record, everything to do with the playback equipment. "As a further point stereo records were limited by phase - they needed to ensure that at various critical frequencies there was no difference in phase between left and right (bass is critical), otherwise the stylus might jump out of a groove. Some digital formats have recordings that contain much out of phase information - creating a holographic type impression. If these contain low frequency sounds out of phase, then these need to be modified prior to be prepared for release on a record. "
- starkparker 4y agoThis is why there are still mastering engineers who specialize in vinyl. See also https://badracket.com/vinyl-mastering/ https://badracket.com/vinyl-mastering/ for more vinyl-specific mastering concerns.
- jlarcombe 4y agoYeah the phase thing is quite a pain, I always thought it was just for really low stuff, but a band I was helping out had a master rejected by the pressing plant for excessive out-of-phase audio even when the passages in question weren't particularly 'heavy'. Since then I've been quite paranoid about it before sending masters off, and it's surprising how many mixes have a load of out-of-phase stereo. It can usually be tamed with some M/S EQ but then you miss the spaciousness in headphones...
- muhwalt 4y agoThis is one of those things I never gave much thought but is super facinating. The technology connections youtube channel just did a video about this, too: https://www.youtube.com/watch?v=3DdUvoc7tJ4 https://www.youtube.com/watch?v=3DdUvoc7tJ4
- brewdad 4y agoI was just going to post this. Others have given some of the math and technical explanation below but if you would like to see this in action with a bit more of the history behind it all, I highly recommend this video.
- foobarbecue 4y agoThe TC video was good, but the link here sure is a faster way to learn the same basic information!
- dylan604 4y agowatching paint dry is faster than getting info out of that video.
- mgdlbp 4y agoVideo of the needle and grooves under an electron microscope: https://www.youtube.com/watch?v=GuCdsyCWmt8&t=301s https://www.youtube.com/watch?v=GuCdsyCWmt8&t=301s
- justinator 4y agoIncredible video!
- IYasha 4y agoI was actually expecting the HN link to be it )
- dylan604 4y agoWhat age range is this channel's target audience? The slow pace and sophomoric description of 2 channel audio at the beginning makes me thing it is aimed at a young audience.
- klodolph 4y agoI will add that the “mid-side” technique is used elsewhere, besides record grooves: - In compressed audio file (such as MP3) - In signal processing chains in the studio (process mid and side channels separately, then convert back to L/R) - In certain stereo microphone recording techniques (there is a type of microphone which records left and right, but with opposite phase)
- tgv 4y agoAlso in FM stereo, if I'm not mistaken. One band contains L+R, the other one, which is not played on a mono radio, L-R.
- b1c837696ba28b 4y agoFM radio: https://en.wikipedia.org/wiki/FM_broadcasting https://en.wikipedia.org/wiki/FM_broadcasting > left and right, but with opposite phase The classic mid-side mic technique uses two capsules. The first (middle) is a cardioid or omnidirectionsl facing the subject, the latter (side) is a figure-8 turned 90 degrees. The capsules should be as close to each other as possible to avoid low-frequency phase errors. The signals are converted to L+R via a simple Mid/Side network: L = 0.707 * (M+S), R = 0.707 * (M-S) which is where "opposite phase" comes into play. https://www.uaudio.com/blog/mid-side-mic-recording/ https://www.uaudio.com/blog/mid-side-mic-recording/
- TylerE 4y agoIt's also kinda related to how NTSC works - the color signal is at a frequency and phase such that it falls inbetween consecutive horizontal lines (e.g. pixels), so that when played on a black and white TV that isn't aware of color, the chrominance (as opposed to luminance) isn't visible since it occurs when the beam is advancing.
- klodolph 4y agoI’m not sure I agree with that explanation of the color subcarrier. The color subcarrier is modulated to a higher frequency, but on an old B&W TV, there are no pixels, only lines. The color subcarrier can appear as a pattern superimposed over the picture if it is not filtered out with a low-pass filter—and indeed, B&W TVs made after the advent of color television contain such a filter, which can be removed if you want to use the TV as a higher-resolution monitor for your home computer (ask how I know...) The two chroma channels are, however, “rotated”, similar to the way mid-side encoding is done. You take a YUV signal, you extract the chrominance UV channels, and then you rotate them to IQ channels. The I and Q channels are then quadrature modulated with different amounts of bandwidth assigned to the I and Q channels. The I channel gets, like, 3x as much bandwidth.
- mikro2nd 4y agoOK, now do quadraphonic...
- corysama 4y agoTyped while you were typing https://news.ycombinator.com/item?id=35440858 https://news.ycombinator.com/item?id=35440858
- corysama 4y agoThen encode a surround sound signal as a Dolby Pro Logic II stereo signal and you’ve got a surround sound record! https://en.m.wikipedia.org/wiki/Dolby_Pro_Logic https://en.m.wikipedia.org/wiki/Dolby_Pro_Logic DPLII was based on the fact that if you invert one channel of a stereo signal, it sounds effectively the same. So, they had some way of encoding front and back signals as some sort of symmetry/anti-symmetry between the left and right signal.
- pnut 4y agoThey actually did that: https://en.wikipedia.org/wiki/Compatible_Discrete_4 https://en.wikipedia.org/wiki/Compatible_Discrete_4
- js2 4y agoDPLII was originally worked out as a blind upmixer using analog circuitry. See this interview with Jim Fosgate, who designed it: https://www.stereophile.com/interviews/1204fosgate/index.html https://www.stereophile.com/interviews/1204fosgate/index.htm... Later Fosgate worked with Roger Dressler at Dolby and Dolby's engineers converted the analog circuit to digital. See these two posts from Dressler for additional detail: https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby-digital.3270616/post-62424523 https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby... https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby-digital.3270616/post-62425841 https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby... The encoder came later, after the DPLII blind upmixer was already designed.
- agentofoblivion 4y agoThat all looks erotic.
- Aldipower 4y agoOh yeah!
- intalentive 4y agoOr stereo signal coming from a single cable.
- jgrahamc 4y agoI was recently in a large shop that sells books, music, etc. and I was amazed at the number of "LPs" (as I used to call them) of music old and new. The one thing that I really like about that format is... cover art. Cover art kind of survived the CD but the large size of a 12" record sleeve means you get real art. I asked someone way younger than me (some students of about 19/20) why they buy records and they expressed how much they like the physical format and owning the music.
- jfengel 4y agoIndeed, there was news last month that vinyl now outsells CDs: https://www.bbc.com/news/64919126 https://www.bbc.com/news/64919126 "Music lovers clearly can't get enough of the high-quality sound and tangible connection to artists vinyl delivers," Glazier said, "and labels have squarely met that demand with a steady stream of exclusives, special reissues, and beautifully crafted packages and discs."
- eesmith 4y agoI bought (and long ago gave away, alas) an LP copy of the Jethro Tull's "Thick As A Brick" because it opened up to a 12-page newspaper, while the CD had a smaller abridged copy.
- lispisok 4y agoReasons I buy vinyl: 1. It's a different listening experience than the "song shuffle on Spotify" that dominates now. It's more a more active and focused listening experience. You put an album on to listen to that album from start to finish. 2. I want to support musicians by buying their albums. However I dont like buying digital music because it doesnt have the permanence a physical object has. I dont like spending money on what's basically ctrl-c ctrl-v files onto my hard drive. CD's are too flimsy. Vinyl has heft. 3. I'm not into the album art that much but a lot of my guests are and like to thumb through my records and look at the art. 4. I'm a hipster contrarian. When vinyl started to get too popular I started buying cassettes too
- grujicd 4y agoRecords for sure beat longevity of most media. I got a 1979 record from a friend. One side was full of dust. I guess it was parked that way on record player for few decades. After simple gentle wash and dry it was as good as new! Of course, if it's scrached it's not good. And if you listen it hundred times it will degrade, but it will still work.
- Eisenstein 4y agoMy great 'aha' moment of 'technology is actually sometimes really simple when broken down' was realizing that magnetic sound recording is just running past a speaker coil at a constant speed while holding something long and ferrous next to it. To play it back do the same thing but plug the coil into the input.
- pl90087 4y agoAside from the contents, let's all take a moment to admire the simplicity of this page. A few animated pictures and everybody got right away what's going on. Absolutely amazing!
- doctorhandshake 4y agoA few years back I had the privilege of working for the New York City edition of the Red Bull Music Academy, and, perhaps unsurprisingly, a large portion of the lectures and general discussion focused on things related to vinyl. One thing I remember standing out to me was a mention by a vinyl mastering engineer that he would manually roll up the bass level on the EQ over the length of the side as the record was cut. He explained that this was because on most record players the tonearm is more or less parallel to the groove at the start of the side and by the end of the side is less so, which decreases bass response, requiring more bass energy in the signal to compensate.
- buildsjets 4y agoI don't think that a constant roll-in of EQ would be helpful. On playback, the stylus is actually parallel to the groove at two positions, both in the middle of the disc, not at the edge, as depicted on a cartridge alignment protractor. https://www.audio-technica.com/en-us/support/audio-solutions-question-of-the-week-how-do-i-align-my-audio-technica-phono-cartridge/ https://www.audio-technica.com/en-us/support/audio-solutions... So you start playing a record and the stylus has a small lateral load bias to one side, has a zero crossing, an small opposite side bias, another zero crossing, and then finishes up with a high lateral load bias on the inner groove and all the female vocals sound terrible due to the extreme sibilance distortion.
- teeray 4y agoIt sounds antithetical to the analog nature of vinyl, but has anyone experimented with digital audio on vinyl?
- empyrrhicist 4y agoMost modern vinyl records have digital processing somewhere in their source. I do remember recently reading about video games on vinyl also.
- crazygringo 4y agoI assume you mean actual binary encoding into the vinyl? Now that's a hacker idea if I ever heard one. I assume the way to do it would be to use a modem the same way the internet operated over dial-up. Listening to the vinyl would sound the same as when you accidentally picked up a phone on the same line, a static-y kind of squeal. It does make me wonder what the maximum practical bitrate would be -- more than phone lines with their severely limited frequency range, that's for sure. Could it handle CD-quality FLAC audio? It also makes me wonder how you'd manage records wearing out. What type of distortion occurs, and how might that affect how you'd spread bits over the spectrum, or would it affect which error correction code you'd use?
- dweymouth 4y ago> Could it handle CD-quality FLAC audio? I doubt it, since CD-quality audio is already objectively better (for human hearing) than analog audio on LPs. The only thing LPs are better at, sound quality wise, is extension into the ultrasonic range of 20-30+ kHz (which we can't hear anyway) but the SNR and distortion metrics are much worse in the ultrasonic band than the audible range. I'm not sure if this is a named principle, but it seems intuitively obvious to me that on any particular encoding medium (magnetic tape, vinyl groove, etc.), you can encode "more" data in an analog way than digital, since with digital encoding you need to be able to make distinct symbols onto the medium, and represent any signal fluctuation with a series of such symbols; whereas with analog encoding a tiny fluctuation in what's recorded to the medium can correspond to a tiny fluctuation in the signal. Of course the tradeoff is that digital data is much more immune to distortion from imperfections in the medium. If the same track width and pit sizes on CDs were used to encode audio in an analog way like LaserDisc does video (the continuous distance between pits being modulated by the signal), no doubt it could encode well into the ultrasonic range and surround audio channels via modulating them into different frequency bands. But it would have its own characteristic "surface noise" and "pops and clicks" just like vinyl.
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- IYasha 4y agoBut wait till you see quadrophonic records!
- roddylindsay 4y agoQuadraphonic CD-4 records from the 1970's encode 4 discrete channels into a single record groove! https://en.wikipedia.org/wiki/Compatible_Discrete_4 https://en.wikipedia.org/wiki/Compatible_Discrete_4 The trick is to encode two additional channels on a 30kHz carrier signal above human hearing range, then demodulate those channels in the receiver.
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- askvictor 4y agoI have a Pink Floyd LP in quadrophonic; never had a record player that could play it in it's full glory though. And now I understand how it works!
- wingineer 4y agoVery clear visual. Does anyone have a similar visual reference for how quadraphonic records work?
- gorkish 4y agoThey work exactly the same way. All of the popular quadraphonic formats work modulating or encoding the four channels together into two signals which are cut just like a stereo record. There were/are a great many schemes for achieving the multichannel encoding/decoding all with inherent advantages, disadvantages, and compatibility with legacy equipment. Dolby Pro Logic (and related successor tech) were probably the most successful multichannel tech that people will be familiar with, though that particular scheme came after the heyday of vinyl.
- Aldipower 4y agoI love nineties styled websites. Clear and precise.
- ozornin 4y agoHm, I thought that stereo vinyl records are recorded in a way that vertical groove profile is V=L+R and the horizontal represents H=L-R. It's backward compatible with older mono gramophones that read only L+R and stereo players do H+V=2L and H-V=2R to decode. Also, while writing this, I realised that it's exactly the same as in the article. Just another way of thinking about it.
- musicale 4y agoAnother reason why mono is better for 12" dance records (another being avoiding stereo image/balance effects in clubs; and if the PA setup is mono anyway then you'll get a real mono mix rather than a summed stereo mix.) I imagine stereo could help a bit with phase effects between speakers, but they would likely still be an issue in multi-speaker setups.
- smoyer 4y agoThis is an amazing example of moving forward without breaking changes ... We could probably do better with our software too. Another interesting example of creating a compatible signal is the addition of chroma information to the black and white NTSC television signal. The original signal was modulated using VSBAM and the chroma signal was added to (predominantly) the high frequencies of the channel.