[HN Gopher] How to pack a stereo signal in one record groove
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How to pack a stereo signal in one record groove
Author : pubby
Score : 217 points
Date : 2023-04-04 03:43 UTC (19 hours ago)
(HTM) web link (www.vinylrecorder.com)
(TXT) w3m dump (www.vinylrecorder.com)
| ozornin wrote:
| Hm, 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.
| teeray wrote:
| It sounds antithetical to the analog nature of vinyl, but has
| anyone experimented with digital audio on vinyl?
| crazygringo wrote:
| I 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?
| CocaKoala wrote:
| You can indeed encode digital data onto a vinyl and then play
| it back meaningfully to a computer -
| http://boginjr.com/it/sw/dev/vinyl-boot/ is somebody making a
| vinyl boot disk and using it to boot DOS.
| crazygringo wrote:
| Ah ha, exactly! Wow.
|
| What's next, encoding a ZIP file onto a wax cylinder?
| roddylindsay wrote:
| DTS is a lossy codec that can encode multiple audio channels
| into normal stereo audio. The encoded waveform sounds exactly
| like a dialup modem.
| dweymouth wrote:
| > 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.
| crazygringo wrote:
| > _it seems intuitively obvious to me... you can encode
| "more" data in an analog way than digital_
|
| It doesn't seem obvious to me, because I'm not talking
| about encoding distinct symbols into the medium. I'm
| talking about using the entire available frequency range to
| encode digital information the way a modem does. And I'm
| talking about using lossless compression as well. And as
| you say, if an LP can encode ultrasonic information, that
| opens up all sorts of extra space for information that is
| useless in analog.
|
| It may very well be the case that an LP couldn't record CD-
| quality audio, but I do very much wonder what kind of
| bitrate would actually be achievable. A dial-up modem is 56
| kbps, using the frequency range 300 hZ to 3.3 kHz. CD audio
| is 1,411 kbps, but vinyl frequency range is from 7 hZ to 50
| kHz, which is 16x wider than a dial-up modem. _And_ you can
| pack _much_ more data into higher frequencies.
|
| So on the face of it, digital CD-quality audio seems like
| it might be very much achievable in theory on vinyl. But
| again, when you account for error correction and
| degradation and particularly distortion, I wonder if you
| could actually get it reliably in practice.
| dweymouth wrote:
| Hmm that's a good point, that you can use the ultrasonic
| bandwidth of the LP, which is useless for analog audio,
| to increase the bitrate. I'd say it's a bit generous to
| give an LP a bandwidth of 50 kHz, especially in the inner
| tracks though. I think what I was getting at would apply
| where the bandwidth of the analog signal you want to
| encode is as wide as the bandwidth of your media though.
| Take compact cassettes, let's say they have a bandwidth
| of 18 kHz and a dynamic range of 60 dB. If you want to
| encode an arbitrary audio signal with a bandwidth of 18
| kHz and with 60 dB dynamic range, you could only do that
| in the usual analog way. But if you wanted to encode a
| digital telephone signal (say at 8 kHz bandwidth, 30 dB
| dynamic range) maybe you could use the 18 kHz cassette
| bandwidth to encode that signal digitally.
| marcodiego wrote:
| Yes. Not necessarily digital audio, but digital data:
| https://en.wikipedia.org/wiki/Flexi_disc
| empyrrhicist wrote:
| Most modern vinyl records have digital processing somewhere in
| their source. I do remember recently reading about video games
| on vinyl also.
| klodolph wrote:
| I 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)
| pjc50 wrote:
| Arguably YUV (luminance plus two chroma dimensions), as used in
| lots of video codecs.
| klodolph wrote:
| Yes, that's a good point. And then in NTSC, the UV is further
| rotated to produce IQ, which are given different amounts of
| bandwidth in the color subcarrier.
| pavon wrote:
| I thought that was where the article was heading when it
| mentioned that horizontal was better (and the unstated fact
| that mono was horizontal), but it still took me a minute to
| realize that the 45 degree pickups are equivalent to midside.
| In (digital) mid-side you encode M=L+R and S=L-R. With this, if
| you breakdown the horizontal and vertical components:
| HL = +L/sqrt(2) VL = +L/sqrt(2) L = sqrt(HL^2 + VL^2)
| HR = +R/sqrt(2) VR = -R/sqrt(2) R = sqrt(HR^2 + VR^2)
| H = HL + HR V = VL + VR = (L+R)/sqrt(2) V =
| (L-R)/sqrt(2)
|
| Note that VR is negative and HR is positive because the sign of
| the pickup is inverted in the diagrams.
| TylerE wrote:
| It'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 wrote:
| I'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.
| dweymouth wrote:
| Broadcast NTSC did actually modulate the color signal into
| a "comb-shaped" frequency spectrum that was overlaid onto
| the complimentary "comb-shaped" spectrum of the B+W signal,
| because they didn't want to have to re-allocate higher
| broadcast channel bandwidths to be able to support color
| (and therefore have fewer channels available). The comb-
| shaped nature of the spectrum is an artifact of the
| discrete lines the picture signal is made up of, and the
| pause between each line when the electron beam reset itself
| and prepared to draw the next line. The fact they were able
| to figure out how to do color in the same bandwidth in a
| backward-compatible way is actually kind of insane, and
| I've seen it mentioned somewhere as one of the, if not
| _THE_ most impressive engineering achievements of the 20th
| century.
| tgv wrote:
| Also 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 wrote:
| FM radio: 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/
| IYasha wrote:
| But wait till you see quadrophonic records!
| ozornin wrote:
| Is that a thing?
| jgrahamc wrote:
| I 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.
| eesmith wrote:
| I 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.
| dylan604 wrote:
| as someone that was a vinyl DJ in a former life that saw the
| transition from vinyl to CDs to where it is now, vinyl is
| absolutely my favorite precisely because of the physicality of
| it. it was the closest to feeling of playing an instrument.
| learning the touch and feel of picking up the stylus cartridge
| without the infamous screeching/scratch sound, how light/heavy
| to touch the platter/spindle/label to push/pull/drag to speed
| up or slow down the record to keep line up the beats were all
| things that reminded of playing an instrument (I played
| woodwinds) with how much air to use, how hard to hit the reeds,
| and the various other physical things to play. there was also
| the fact that it had to be played and not programmed that i
| appreciate from playing vinyl.
|
| as a medium for just sitting back and enjoying some tunes at
| home, it's gotta be the worst! LPs might give you 3,4,5 songs
| per side, but you still would have to get up and flip it or
| find another LP. singles like 45s or 12"s were even worse as it
| was one song at a time. a 12" at 45rpm only has somewhere
| around 10mins of recording. an LP at 33rpm might have 20-ish
| minutes. so that's a lot of interruptions in the music flow. if
| you really enjoy that manual switching out, then i'd suggest
| just taking the next step and being a DJ constantly mixing
| track to track.
| grujicd wrote:
| For me it's the other way around. Striming or local digital
| collection trigger my "let's skip to next song" impulse.
| While with LP I'll listen to entire album. So vinyl is for me
| medium of choice for sitting and listening at home.
| dylan604 wrote:
| This is where the cassette or CD are great mediums for
| listening to the full album (using the cassette's autoflip
| mode).
|
| recently, i started going back through music collection to
| listen to full albums instead of the streaming track to
| track as you've mentioned. it was a very nice change of
| pace from just hearing random tracks continuously. it seems
| to be popular enough that even youtube has Full Album
| titles. the playlist assembling full albums are rather
| annoying for those albums with no gaps between tracks, but
| are better than nothing if that's all that's available. so
| now it's best of both worlds where it is streaming but
| still the full album experience.
| lispisok wrote:
| Reasons 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 wrote:
| Records 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.
| jfengel wrote:
| Indeed, there was news last month that vinyl now outsells CDs:
|
| 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."_
| [deleted]
| Eisenstein wrote:
| My 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.
| PopAlongKid wrote:
| Trivia: 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.
| wingineer wrote:
| Very clear visual. Does anyone have a similar visual reference
| for how quadraphonic records work?
| gorkish wrote:
| They 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.
| roddylindsay wrote:
| Quadraphonic CD-4 records from the 1970's encode 4 discrete
| channels into a single record groove!
|
| 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.
| [deleted]
| askvictor wrote:
| I 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!
| muhwalt wrote:
| This 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
| brewdad wrote:
| I 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.
| IYasha wrote:
| I was actually expecting the HN link to be it )
| dylan604 wrote:
| What 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.
| rideontime wrote:
| I'm 30 or 40 years old, and this is one of my favorite
| youtube channels. :)
| svckr wrote:
| I am also 30 or 40 years old. I'm Schrodingers millenial.
|
| I quite enjoy the delivery of technology connections. A
| nice change of pace imo, compared to other youtubers that
| edit out every millisecond of quiet time between words and
| sentences.
|
| But I'm not watching the videos to learn new stuff either
| rideontime wrote:
| Slower videos just means they last longer, and that I can
| keep up with them while I'm crocheting.
| heleninboodler wrote:
| I absolutely love this channel even though I find the guy's
| delivery excruciatingly slow and his style very annoying. I
| watch it on 2x to solve the first problem and just cringe
| through the dorkiness.
| netsharc wrote:
| Yeah, the dorkiness can be a bit too much sometimes. One
| time he made a dorky joke, and then made a meta-joke
| addressing how dorky that joke was, and it was extra
| cringe...
| LegitShady wrote:
| I think the simple explanations are just that guy's style. He
| often has oddball videos about stuff you've probably seen but
| never thought about in depth - from lava lamps to
| retroreflectors.
|
| He gets quite a few views and educates a lot of people. No
| need to look down on it - if it isn't for you thats ok.
| fknorangesite wrote:
| > The slow pace and sophomoric description
|
| This seems needlessly condescending. 1.5x is your friend.
|
| > a young audience.
|
| Or just people who don't know much about 2 channel audio (or
| whatever else he's talking about this week/month/whatever).
| Not everyone does, after all.
| dylan604 wrote:
| It's not playback speed that's slow. It's the sophomoric
| definition of stereo. It's the absolute dragging of the
| feet to deliver that definition that isn't even a good
| description of stereo.
| [deleted]
| foobarbecue wrote:
| The TC video was good, but the link here sure is a faster way
| to learn the same basic information!
| dylan604 wrote:
| watching paint dry is faster than getting info out of that
| video.
| mgdlbp wrote:
| Video of the needle and grooves under an electron microscope:
| https://www.youtube.com/watch?v=GuCdsyCWmt8&t=301s
| justinator wrote:
| Incredible video!
| incanus77 wrote:
| I frequently find myself wanting to think more critically and
| guess about things like this. If I had thought a bit further
| before reading (one needle, but what is the groove like?) I
| would gotten to assuming that it was one dimensional, but then
| stepped from there to it actually affording two dimensions.
|
| Does anyone have recommendations for reading or exercises to
| improve this kind of thinking?
| mikro2nd wrote:
| OK, now do quadraphonic...
| corysama wrote:
| Typed while you were typing
| https://news.ycombinator.com/item?id=35440858
| doctorhandshake wrote:
| A 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 wrote:
| I 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...
|
| 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.
| lqet wrote:
| Now _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 "Fullschriftverfahren" 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
|
| [1] https://grammophon-platten.de/page.php?530
| PopAlongKid wrote:
| >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=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 wrote:
| This is why there are still mastering engineers who
| specialize in vinyl. See also https://badracket.com/vinyl-
| mastering/ for more vinyl-specific mastering concerns.
| jlarcombe wrote:
| Yeah 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...
| jameshart wrote:
| > A really elegant solution, which somehow reminds me of the
| cover of GEB
|
| The thing is, when you play a record on a GEB phonograph, you
| run the risk of your phonograph vibrating itself apart.
| timmg wrote:
| > (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
|
| I _think_ the way they do it with FM radio is: one channel is
| A+B and the other is A-B. The A+B channel is the "mono"
| channel for backward compatibility. (Then they add/subtract to
| get left/right: (A+B)-(A-B)=B; (A-B)+(A+B)=A.)
|
| Pretty elegant solution, IMHO.
| phkahler wrote:
| I don't recall why or how, but the A-B channel is of lower
| bandwidth, or otherwise more likely to drop out. Hence when
| you're starting to lose FM, you may find it dropping to mono.
| timmg wrote:
| I think the reason is less interesting: when you start to
| go out of range, your radio _thinks_ there is only a mono
| signal, so it switches to mono mode.
|
| Same reason "static" on your TV is black and white. Your TV
| didn't detect a color signal, so it is looking for the
| black and white one.
|
| (For anyone old enough to remember static on their tv :)
| Aldipower wrote:
| I love nineties styled websites. Clear and precise.
| corysama wrote:
| Then 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
|
| 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 wrote:
| They actually did that:
| https://en.wikipedia.org/wiki/Compatible_Discrete_4
| js2 wrote:
| DPLII 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.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...
|
| https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby...
|
| The encoder came later, after the DPLII blind upmixer was
| already designed.
| intalentive wrote:
| Or stereo signal coming from a single cable.
| pl90087 wrote:
| Aside 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!
| agentofoblivion wrote:
| That all looks erotic.
| Aldipower wrote:
| Oh yeah!
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