Analog Memory?

  1. "Analog" Memory?

    Is anyone aware of physical or mathematical reasons why "analog" memory is not possible? That is, a system that takes in a continuous waveform, saves it, and then later releases the same continuous waveform without any sort of sampling or interpolation. I certainly can't think of a way to do this. But the point of my question is about the existance of a mathematical theorem or physical law that makes this type of system impossible. This seems like it may belong in the Engineering forum, but I think it is more of a question about the underlying physics rather than any sort of engineering issue.
  2. jcsd
  3. Sounds like a wax cylinder.
  4. AlephZero

    AlephZero 7,248
    Science Advisor
    Homework Helper

    I guess you are too young to have known when vinyl was the main option for music recording (good quality analog tape recorders and reel-to-reel tape were way too expensive and fiddly for most people, and cassette tapes were the equivalent of over-compressed MP3 files today).

    Or, you assume that "newer technology" automatically means "better quality" :devil:
  5. Huh? Im just saying that what he is describing sounds like a wax cylinder (among other things). You think I know about wax cylinders but not vinyl? :confused:
    Last edited: Feb 27, 2014
  6. Even a mechanical systems have an 'analog' memory. On a a roller coaster ride, the car follows the curve of the track without any digital sampling or interpolation. The memory is the layout of the track and all cars will follow the same wave pattern.
  7. This seems like a really stupid question now :/
  8. berkeman

    Staff: Mentor

    Not stupid at all. Great responses :smile:
  9. AlephZero

    AlephZero 7,248
    Science Advisor
    Homework Helper

    I've learned the hard way the second guessing what other people know is often a bad plan.

    It would be quite possible for somebody to know about wax cylinders from a history lesson, but have never actually heard a vinyl record played on high-quality equipment (and broadcasting the music on FM radio with a high frequency limit of 16kHz doesn't count as "high quality.")
  10. Drakkith

    Staff: Mentor

    Not at all. I actually learned something.
  11. sophiecentaur

    sophiecentaur 14,717
    Science Advisor
    Gold Member

    Did you ever hear of the 'Bucket Brigade' analogue shift register / delay?
    (Ref this wiki link)

    That could qualify for what you're after and there are no 'moving parts'.
  12. In the case of CDs vs vinyl, it does. Sadly, poor mastering has ruined the quality of a great many CDs, but in terms of actual audio fidelity, the CD beats the vinyl record hands down.
  13. analogdesign

    analogdesign 834
    Science Advisor

    The bucket brigade is a sampled-data device so it strictly a continuous waveform processing device as the OP asked (although it obviously can be used on a continuous signal if Nyquist is respected and a reconstruction filter is used).

    Another option is a Mercury Delay Line. This was used as an early analog memory in Radar systems during and after WWII. It was also used as one of the first digital computer memories.
  14. sophiecentaur

    sophiecentaur 14,717
    Science Advisor
    Gold Member

    The most impressive analogue memory / delay line I have come across was the 20ms, field store quartz delay lines that were used in the early analogue TV standards converters. They carried a video signal and the delay was achieved by multiple reflections on the (internal) faces of a quartz polygon, a couple of cm thick and the size of a dinner plate. Pretty impressive stuff and a lot more compact than the digital field stores that replaced them (at the time).
  15. Multi head tape recorders and spring delay lines were a form of analogue memory used years ago. Analogue data put in one end came out the other a short time later (somewhat distorted usually).

    I suppose it might be possible to bounce an analogue signal off the moon. I calculate you could store about 2.5 seconds worth in the round trip distance.
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