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Digital LP

All the hipster benefits of real vinyl on real old-school turntables, but with digital audio.
  [vote for,

A compressed digital audio data stream is fed into a modem, producing an analogue signal which drives the cutting head on a vinyl mastering lathe. The LPs are pressed as usual onto vinyl.

For playback, a normal quality turntable and pickup are used. The pickup sends its analogue signal to a modem, which provides the original compressed data stream to feed into a D-A converter. This drives the speakers via the usual amp &c.

pocmloc, Feb 25 2016

Wiki "Modem" arcticle. https://en.wikipedia.org/wiki/Modem
[scad mientist, Feb 28 2016]


       Could play those LPs using the currently available optical turntables. [+]
whatrock, Feb 25 2016

       You forget a coil heater to make the sound warmer.
the porpoise, Feb 25 2016

       // a coil heater to make the sound warmer //   

       Recently I heard a musician saying his tubes amp sounds great because the heat of the filaments is above normal and you know, warmer tubes produce warmer sound :-p
piluso, Feb 25 2016

       Needs a layer or two of error correction / concealment.
csea, Feb 25 2016

       Doesn't the needle emit some sound directly? That's not a problem when the sound matches what's coming out of the amp, but it might be an issue if it was screechy modem sounds.
scad mientist, Feb 25 2016

       I don't think you'd have the bandwidth to play anything in real time using this method. Pretty sure you'd have to play the track first to "download" the data into a buffer and play it from that. I'm also guessing that a song would need several LPs to get all that data in.   

       I could be wildly off on this since I'm pretty rusty with my digital audio knowledge, but I'm sure it's not a one to one tradeoff, analog vibration to data on off signals. For instance, a 32 bit waveform would require you take one pulse, or one wiggle of the analog record player needle and chop it into a bunch of pieces that you can put back together to draw that wave again. So to draw one hump of that wave, you'd need the needle to wiggle, that is, indicate on or off, 32 times, compared to the analog playback just having the needle move once.   

       But it's a cute idea as long as you don't mind it not playing in real time, or playing very, very, very slowly in real time so: [+]
doctorremulac3, Feb 25 2016

       I also wondered about bandwidth, but I assumed that compression could overcome that. I'm thinking I can live-stream digital audio down my telephone wire at a much higher quality than analog audio over the same wire.
pocmloc, Feb 26 2016

       You're sending a lot more information with that digital audio. With the analog you're just wiggling your power up and down to make the speakers shake.   

       The way you digitize an analog waveform is to cut it up in little slices like a loaf of bread. So if the top of the wave is say 5db and the bottom is -4db. You have the first slice taken at 1db, second at 2 db till you get to the peak of the wave then you go back down. The higher the resolution the more slices you're taking and the smoother picture you get of the wave.   

       Each little slice is a piece of information you need to send just to convey one little wiggle of the needle on a record player.   

       But like I said, impractical but interesting inventions are pretty much what the HP is all about. I'm very proud of my mechanical internet which as I pointed out, would do the job at 1 millionth the efficiency at several million times the price.
doctorremulac3, Feb 26 2016

       [dr3] The reason TV and radio has converted to digital is that you can squeeze far more data into the same (analog) bandwidth. Mostly because of compression.   

       But the problem with vinyl is that the bandwidth changes from rim to hub...   

       [edit: I very nearly posted an idea just now for a vinyl record that played with constant linear velocity, changing the rpm to match the needle position. But then I googled and found this has already been done, and was a commercial failure.]
mitxela, Feb 26 2016

       //The reason TV and radio has converted to digital is that you can squeeze far more data into the same (analog) bandwidth. Mostly because of compression.//   

       Well, yes, but you're using the same method at one level of sending information with both analog and digital: electrical pulses, be they translated into LEDs, lasers, radio waves etc.   

       With analog you're not fully utilizing how fast those pulses can be, which is very very fast.   

       But you do agree that real time digital playback from vinyl isn't a possibility, at least at standard 33 1/3rd RPM, yes?   

       If somebody was really clever they'd be able to figure this out: "How fast would a mechanical audio turntable need to spin to get say, 1gps of data output?"   

       And by the way, what portion of the people reading this know that a turntable turns at 33 1/3rd revolutions per minute? And how many can say how fast a 7" record turns? Hint: The RPM of the smaller record is what they're actually referred to. I'm guessing that those born after 1990 wouldn't know this.
doctorremulac3, Feb 26 2016

       //But you do agree that real time digital playback from vinyl isn't a possibility, yes?//   

       No, I don't see why it wouldn't be possible. Analog signals have bandwidth too - an FM broadcast occupies a certain amount of the EM spectrum. A digital radio broadcast takes up less of the spectrum.
mitxela, Feb 26 2016

       So 33 1/3rd would give you the same bandwidth? Eh, maybe, but that would surprise me.   

       I'm thinking you've got a limited amount of "wiggles" on vinyl, a few hundred per inch, before the needle starts bouncing out of the groove like a car hitting a speed bump. Electrical pulses have no such limitation.   

       An old, pre DVD laser disc, which is basically an optical vinyl player with a laser instead of a needle to get over the physical limitations of a wiggly slot with a needle in it turns at 1,800 RPM so I think you might be mistaken. Of course those carry video information as well as an audio track but 1,800 is a lot faster than 33 & 1/3rd.
doctorremulac3, Feb 26 2016

       Well, human hearing goes up to about 20kHz, so I assume a vinyl record has at least 20kHz of bandwidth at its smallest radius. Probably double that at the rim.   

       So I suppose that implies a bitrate of less than 20kbits/sec, which would be enough for low-quality audio reproduction. 'Telephone quality' is usually 8kbits/sec, but MP3s can be as high as 320kbits/sec, so you're right in that it wouldn't be as high quality as the analog signal alone.
mitxela, Feb 26 2016

       I agree with [mixtela]. Here's why. A 56k modem can transmit over a phone line that has MUCH poorer audio quality than an LP. The phone line is limited to about 3.2KHz and in digital phone systems is sampled at 8 bit 8KHz. LPs have a much higher bandwidth. If we just say that they are as good as a CD, that's 16 bit sampling at 44kHz. which is about 10 times. I'm sure an LP is less noise than the 8 bit quantization causes, but it might not actually be as good as 16 bit, so lets say 5x instead of 10x just to be safe. That means that a 280kps modem is feasible, which is a pretty high quality mp3. I'm guessing you could push it a lot farther than this, but I'm pretty confident that 280kbps is achievable.
scad mientist, Feb 26 2016

       Actually if you presume the analog signal is a sine wave or a summation of sine waves then you need only a few data points to approximate it.
RayfordSteele, Feb 26 2016

       //I'm pretty confident that 280kbps is achievable.//   

       Are you sure enough to call this "solved with 100% certainty"? We're talking real time, same resolution as a regular record with no increase in speed. I'm still dubious.   

       If you're not sure, I need to call somebody on this. I'm pretty sure anybody who works at Bell Labs could answer without any hesitation. I'd bet even the receptionist or the parking lot attendant probably knows. This is exactly what they deal in.   

       Who wants to contact them? If nobody else will, I'll write them an email. I'm busy today but now this question is bugging me.   


       Does somebody really know or do I write these guys?   

       Ok, I'll write them. I'll post what I get a definitive.
doctorremulac3, Feb 26 2016

       Go for it, I'm interested too.   

       I looked up some numbers to back up what I was saying earlier. For radio broadcasts, FM stations are spaced 500kHz apart. DAB radio in the UK is variable based on the desired quality, but the BBC broadcasts ten 128kbps stations in a 1.7MHz block. So the digital broadcasts are able to fit nearly three times as much audio into a given chunk of spectrum.   

       There's an equation (Shannon-Hartley) that lets you calculate the maximum bitrate for a noisy channel, but I usually just go with bitrate ~= bandwidth. 20kHz was a worst-case guess, and googling tells me that some LPs supposedly have bandwidths of 150kHz. If so, you could store a 128kbps stream in that.   

       [Ian] My condolences.   

       [scad] What you're saying makes sense, but I don't know, weren't phone lines improved to enable higher modem speeds? Otherwise they could have started off at 56k instead of slowly speeding up.
mitxela, Feb 27 2016

       Sent this. I'll let you know if they respond.   


       Can you direct me to someone in your company might be able to answer a general technical question? I was part of a discussion about data storage and specifically how very old data storage methods might translate to modern data storage numbers.   

       There's a famous picture of Bill Gates holding a CD atop a stack of paper several yards high representing how much storage capacity this new method represented compared to printed pages.   

       My question is in a similar vein. How much data might theoretically be stored on an old vinyl record and what method might be used, and what bandwith for real time transmission might be possible with a record turning at the old standard 33 1/3rd rpm?   

       This is of course just for fun but I thought somebody in your company might enjoy taking a stab at this thought experiment.   

       Thank you,"
doctorremulac3, Feb 27 2016

       My husband collects. He just does. Mostly vinyl. We have an entire room dedicated to vinyl. Actually a room and a half. The rest of our flat has the walls lined with shelves of CD's and DVD"s, except for the overstuffed bookcases which surprisingly enough, hold books.   

       My husband has not played anything on his turntable since we reunited 5 years ago, so maybe even 10 years or more. Not once. We just look at them. We stare at them and watch his collection grow. It gets dusty. He amuses himself by dusting his collections once a month.   

       The moral of this story is; Don't let your husband collect vinyl, if he's not going to actually play it. It just takes up valuable, usable space, that I could use for other meaningful purposes, like hanging tapestries on the wall or something.   

       So a + for the idea, if it would motivate my husband to buy, and listen, to vinyl. Not just stare at it.
blissmiss, Feb 27 2016

       Back when I was in the music biz in my youth, CDs and cassettes were how people purchased their music, but I do have in my possession a vinyl pressing of my band from Italy. There were also vinyl pressings available in South Korea though I never got my hands on one.   

       For some reason I really treasure this goofy thing. I grew up with vinyl so I'm glad I can say I was actually part of the vinyl age sort of.   

       By the way, if you ever play an actual gold or platinum record you'll find it's probably not actually the band shown. I've never done it as you'd have to pry the things out of their frames and they're glued on so you'll probably wreck the thing but I'm told, from people who probably got drunk and decided to play their gold records that it's invariably something completely un-related. If you're a heavy metal band for instance they'll give you a Barny's greatest hits LP with your label on it.   

       There's your useless trivia for the day.
doctorremulac3, Feb 27 2016

       The speed increase was primarily a result of them finding ways to maximize the use of the available audio bandwidth. Some line quality improvement did come into play, but that was early on: the biggest improvement being the legal action that forced the phone companies to allow direct connection to the phone lines rather then relying on coupling using audio through a standard handset. For those interested in an good overview, the Wikipedia Modem article is interesting [link]. After reading that I did find that my previous analysis had a bad assumption. 56kbps modems actually use more than the 3.2kHz bandwidth of the telephone system, so that rate could only be used for downlink from the digital 64kbps line at the phone company across the short analog line to the house which is not limited to 3.2kHz. I think this means that the ISP had to have a direct digital link to the phone company to work. The fastest modems that could work across the 3.2kHz limited phone system were the 33.6kbps modems. Apparently this is very close to the theoretical "Shannon limit".   

       So where I said that 280kbps is a pretty sure thing, that should have been 168kbps (33.6 x 5), which still isn't too bad for mp3s. Not to mention that I think I was being very conservative with the bandwidth of an LP compared to a phone line by only applying a 5x multiplier.
scad mientist, Feb 28 2016

       Can you break down for me what the actual signal in a modem is? I guess it's conveying on/off signals by varying frequency and amplitude but how is it doing it?   

       So if I want to transmit: 0100100.01001010....etc where do I put these on off signals in a carrier wave or whatever it is that's traveling through a modem? Would you have a certain frequency bleep for a zero and another one for a 1? Basically my question is how does analog data transmission work?
doctorremulac3, Feb 28 2016

       As I understand it, a modem turns data into bleeps of different frequencies. But each bleep can carry more than one bit of data. I just glanced at the wiki page (will read it later) and I wasn't aware that a 33.6k modem transmits as many as 10 bits per symbol - that implies there are 1024 different frequencies it uses.   

       So your example of 0100100.01001010 could be transmitted in less than two beeps (not accounting for all the error checking).
mitxela, Feb 28 2016

       //there are 1024 different frequencies it uses.   

       So your example of 0100100.01001010 could be transmitted in less than two beeps (not accounting for all the error checking).//   

       Ok, now we're getting somewhere. (I think) Does amplitude figure into it as well? That is, does a certain wave height signify something different than a different wave height?
doctorremulac3, Feb 28 2016

       There's frequency shift keying, amplitude shift keying, phase shift keying, and many more combinations / more complicated forms of modulation that wikipedia will be much better at explaining than I am.
mitxela, Feb 28 2016

       10-4. I'll check it out.   

       But to get to the bottom line, if you record a 56K or a 256k modem signal into a record and play it back, I know it'll sound the same to the ear, but how much of that data is actually preserved by a little needle wiggling in a plastic slot?   

       THAT'S the question.
doctorremulac3, Feb 28 2016

       Now I'm wondering if anyone has ever constructed a data stream, which, when sent to a modem, produces a musical sound?
pocmloc, Feb 28 2016

       +. Nice idea in itself. Given for posting the link on portable flagpole.
pashute, Jul 25 2017

       Why thank you most gracious sir.
pocmloc, Jul 25 2017


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