Vinyl & needle magnified 1000x

Discussion in 'Audio Hardware' started by dianos, Nov 7, 2014.

Thread Status:
Not open for further replies.
  1. quadjoe

    quadjoe Senior Member

    I think we're all getting our units mixed up here (I know I am, and even used the wrong symbol in a couple of posts) so, just for reference here is a list, and I'll start off with typical groove dimensions:

    Typical groove dimensions (recording groove contour, RIAA dimensional standard http://www.aardvarkmastering.com/riaa.htm , (in cross section):

    Included angle: 90° + 5°
    Bottom radius: 0.00025" (max.) [0.0006 cm]
    Width, monophonic: 0.0022" - 0.0032" [0.0056 cm - 0.0081 cm]
    Width, stereophonic - instantaneous: 0.0010" (min.) [0.002540 cm (min.)]

    Mil = 1/1000 " (o.oo1" ) = 25.40 μm

    Units:

    nanometre (nm) = 1/1,000,000,000 m or 1E-9m = 1 angstrom (this is where I screwed up I used the notation for micrometre)
    micrometre (μm) = 1/1,000,000 m or 1E-6m
    millimetre (mm) = 1/1,000 m
    centimetre (cm) = 1/100 m
    decimetre (dm) = 1/10 m

    a metre (or meter in the US) = 1.0936 yard

    Notice that the groove dimensions are given in decimals of a centimetre (in brackets).

    Light wavelengths are measured in nanometres (billionths of a metre), but the angstrom was formerly used.

    Sound wavelengths are measured in depending on the medium through which they propagate, metres or centimetres. Here's a useful chart:

    http://www.dpamicrophones.com/en/Ordbog.aspx?entryid={7093D71F-C139-4D8B-BB9B-0F84B37FA502}

    Please note that the size of the sound waves cut into the vinyl is dependent on a variety of factors as others have previously noted in this thread.

    Hope this helps with this very interesting discussion. ggergm, I'm beginning to think that you'll remain at least an order of magnitude away from being able to say that a stylus has to trace a sound wave as small as a wave of light. I'd like for some experts to chime in on this discussion. Not that it makes any difference, but it would be cool to know.
     
  2. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    You're close, Dale H. Positive and negative peaks on a scope are caused by peak velocity of the tip. For sine wave programme content this happens at zero crossing points of the physical groove, ie where stylus location is bang on the line of the groove. It is where the groove has the steepest angle with its ordinary line.

    In practice groove seldom gets entirely too tight even for a conical to 'fit', because curvature is limited to avoid that during mastering. But long before it doesn't 'fit', a real stylus changes its contact location as it traces a curve, versus an 'ideal' sharp cutting edge - and this causes harmonic distortion because the groove is being 'read' at the 'wrong' time if you get my drift. So harmonic distortion is the main penalty for fat stylus in tight curves, typically.
     
    OcdMan, missan and DaleH like this.
  3. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    At 1Khz, a recorded level of -30dB (ref 5.6cm/s) has a physical groove which deviates from 'straight' by less than the wavelength of visible light. It happens all the time !
     
  4. The FRiNgE

    The FRiNgE Forum Resident

    Yes, I understand the complexity of the groove, and styli which are too large to track higher frequencies accurately, "pinch effect", tracing distortion, etc. I was responding to a 20kHz tone, and the "radius" of the half cycle, ie: groove radius derived from frequency period and linear speed of the innermost groove. The discussion had shifted to the record groove at 20kHz may be near the physical wavelength of light. However the "radius" of a sinusoidal tone does not have a fixed radius. The mathematics are not that simple. (The calculations do not seem to be correct, please read previous comments) That is what is "beyond" me at the moment.

    My response is not applicable to the complex physical shape of a music signal in the groove. I am referring only to a single 20kHz tone .. in response to its physical size as cut in a record groove. A stylus has a radius, elliptical is biradial; A pure tone or "sine wave" cut to a record does not have a fixed radius. (or I think should not) Sine waves do not exist in air. (sound propagates as periodic "waves" of compression and rarefaction of the molecules of the substance producing sound) However a pure tone as represented in the (monophonic) record groove, takes on the physical shape of a sine wave.
     
    Last edited: Nov 13, 2014
  5. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    Physical length of a 20kHz cycle in a groove is much longer than wavelength of visible light. But groove displacement from a dead straight line for the tiny quiet levels of sound to be found in real records is far smaller than the wavelength of visible light. A stylus routinely transcribes movements which are much smaller than the wavelength of visible light !

    A separate issue with the wavelength of light is that it is typically much larger than features one is interested in to see or inspect here, such as groove wall texture or stylus polish or even stylus wear features. So optical microscopes simply can't cut it, and that is why it's so difficult to inspect interesting detail optically. SEM like the images in the OP are needed, but that is a serious venture to perform and beyond most amateurs, hence why so few detailed images unfortunately.
     
    The FRiNgE likes this.
  6. GreatTone

    GreatTone Forum Resident

    Location:
    Falls Church, VA
    I thought stylus wear was visible via an ordinary 200x microscope? The lighting needs to be modified of course.
     
  7. John Moschella

    John Moschella Senior Member

    Location:
    Christiansburg, VA

    Yea I know. I don't understand it either. The effective contact area (or length) of the stylus is the key issue in my mind. I don't see how a 75 um stylus can resolve high frequencies.
     
  8. John Moschella

    John Moschella Senior Member

    Location:
    Christiansburg, VA
    Included angle: 90° + 5°
    Bottom radius: 0.00025" (max.) [0.0006 cm] = 6 um
    Width, monophonic: 0.0022" - 0.0032" [0.0056 cm - 0.0081 cm] = 56-81 um
    Width, stereophonic - instantaneous: 0.0010" (min.) [0.002540 cm (min.)] = 25 um

    You can measure light in an unit of length you want, so if blue light is 4500 A = 450 nm = 0.45 um

    Visible light is roughly half a um.
     
  9. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    Just about visible yes. With a lot of care one can see wear patch shape well enough with about x600, but not in any real detail such as surface grain/polish, voids/cracks etc that's what I mean about optical limitations due to wavelength.

    @John_Moschella those groove dimensions you posted are static. The truly tiny dimensions arise transcribing minute detailed modulations in the groove, which are smaller than the wavelength of visible light all the time.
     
  10. Don Hills

    Don Hills Forum Resident

    Take a moment to think about what shape the groove takes when you record a square wave... :)
     
    The FRiNgE likes this.
  11. The FRiNgE

    The FRiNgE Forum Resident

    No record, nor cutting head, nor stylus comprehends the square wave, not even the ocean can produce one. Only in the inner being of an oscillator, or digital sound recording does the square wave exist, almost, and as square as a wire or transistor or tube will allow!
     
    Last edited: Nov 14, 2014
  12. Antares

    Antares Forum Resident

    Location:
    Flanders
    I'll say that's wishful thinking, LD and more than often doesn't bear out in practice. And the boss has gone on record here stating that he only cuts for the "big boys school setups". I'll wager that doesn't include a lot of conical and elliptical styli in this world.
     
  13. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    It would be a perfect triangle wave. Barring RIAA effects, which alter the shape somewhat - but still essentially a triangle wave. 'Corners' or peaks of the triangle wave correspond to transitions of the squarewave.
     
  14. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    It would be a perfect triangle wave. Barring RIAA effects, which alter the shape somewhat - but still essentially a triangle wave. 'Corners' or peaks of the triangle wave correspond to transitions of the squarewave.
     
  15. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    Hi Antares - yes I don't mean that mastering is somehow intentionally dumbed down to cope with fat styli - what I mean is that in practice other considerations make the result tolerant of all profiles though at harmonic distortion penalty for fat styli. ie there is always a maximum permissible stylus acceleration for trackability, perhaps c 800-1000G typically. AFAIK in ye olde days, mastering could involve an 'acceleration limiter' which effectively prevented a cutter from creating grooves with excessive curvature. Curvature = stylus acceleration=slew rate of signal. Maybe these days it doesn't happen, but it's G forces that ultimately limit curvature rather than 'stylus fit'. From a playback perspective it's moving mass that matters more than stylus size in this respect- ooo er that came out a bit rude !
     
  16. Antares

    Antares Forum Resident

    Location:
    Flanders
    Thanks LD. I certainly agree that dynamic considerations can be an even more important factor for trackability than stylus size vs. groove curvature, but the latter is still something that sticks in people's heads after looking at the picture in the opening post. As it happens, I was reading a somewhat related discussion recently here, from which I'll take the liberty to copy a little example illustrating that, depending on the cutting signal level, a stock DL-103/103R with 0.5 mil. conical stylus for instance, could easily get into trouble at only 10 kHz on inner grooves (purely from a static dimensional standpoint). I won't translate the whole text as the numbers should be self-explanatory, but wouldn't this be a severely limiting factor for clean tracking/tracing of even moderately high frequencies then (even before bringing dynamics into the discussion)?

     
  17. VinylRob

    VinylRob Forum Resident

  18. drh

    drh Talking Machine

    His original patent application actually contemplated disks as well, but he opted to produce cylinders because of their theoretical superiority in keeping a constant surface speed throughout their play. Mind you, in practice, at the very high rotational speeds at which they ran (160 RPM was standard for the moulded ones), they were extremely prone to flutter and, if the least bit out of round, high frequency wow. Finding an antique player that runs at rock steady speed and doesn't warble is a bit like finding the Holy Grail or the Loch Ness Monster.
     
    Mr Bass likes this.
  19. Wasatch

    Wasatch Music Lover!

    Very Cool Pics!
     
  20. Luckydog

    Luckydog Active Member

    Location:
    london, uk
    Hi Antares, yup I read german well enough to get lini's post. But it doesn't work like that - groove shapes are velocity cut, curvature is simply down to slew rate of programme signal - which depends on both frequency and level when thinking about sine waves. In real programme material, very high frequencies naturally have far lower levels so curvature doesn't become a strict issue with stylus fit typically. But yes, harmonic distortion always applies all the time to all styli in all grooves, simply because the stylus is not the same shape as the cutter head - if it was it would recut the groove !
     
  21. DaleH

    DaleH Forum Resident

    Location:
    Southeast
    It's good that most fancy needle shapes also usually have low effective tip mass. I can't count the times I've read people say that inner groove distortion became a non-issue when they got an AT440mla.:) Of course I don't recall any DL103 users complaining about IGD either.:shrug:
     
    Heckto35 likes this.
  22. One_L

    One_L Forum Resident

    Location:
    Lower Left Coast
    Found this video that's related as well.

     
  23. quadjoe

    quadjoe Senior Member

    Here's an image I really like, it shows you how very fine the groove on a record really is. Think about how large this image makes everything look, but even so, it's really just the tip of the stylus that sits in the groove. Amazing isn't it?

    [​IMG]
     
    DaleH likes this.
  24. DaleH

    DaleH Forum Resident

    Location:
    Southeast
    I think the important part to me isn't the 99% that most any needle can track/trace but the last 1%. A good tracker is the most important but a good tracer separates the wheat from the chaff. About the most natural sounding one I have is my DL103 with a DIY retip. It has a cactus thorn cantilever with a diamond chip shibata tip from a bonded stylus (without the bonded shank part).
     
  25. Antares

    Antares Forum Resident

    Location:
    Flanders
    Hi LD, - But none of this affects the wavelength of the groove modulation as calculated, does it - regardless of curvature or amplitude? A 10 kHz tone is still represented by a 10k cycle modulation, or not? Just trying to understand.
     
Thread Status:
Not open for further replies.

Share This Page

molar-endocrine