Mark Waldrep, aka Dr. AIX, has been producing and engineering music for over 40 years. He learned electronics as a teenager from his HAM radio father while learning to play the guitar. Mark received the first doctorate in music composition from UCLA in 1986 for a "binaural" electronic music composition. Other advanced degrees include an MS in computer science, an MFA/MA in music, BM in music and a BA in art. As an engineer and producer, Mark has worked on projects for the Rolling Stones, 311, Tool, KISS, Blink 182, Blues Traveler, Britney Spears, the San Francisco Symphony, The Dover Quartet, Willie Nelson, Paul Williams, The Allman Brothers, Bad Company and many more. Dr. Waldrep has been an innovator when it comes to multimedia and music. He created the first enhanced CDs in the 90s, the first DVD-Videos released in the U.S., the first web-connected DVD, the first DVD-Audio title, the first music Blu-ray disc and the first 3D Music Album. Additionally, he launched the first High Definition Music Download site in 2007 called iTrax.com. A frequency speaker at audio events, author of numerous articles, Dr. Waldrep is currently writing a book on the production and reproduction of high-end music called, "High-End Audio: A Practical Guide to Production and Playback". The book should be completed in the fall of 2013.

14 thoughts on “Mythbusters: CDs Optical Properties Affect The Sound?

  • You wrote, “provided the clocks are completely reconstructed…” Various jitter reduction schemes have been in use for decades, but having the timing of the data at the DAC completely independent of the transport is only recently becoming common, and, sadly, is still not universal – as I pointed out in a previous post. Did the reviewer specify on what equipment he heard this difference?

    • Reclocking has been around for a very long time. My point is that reclocking or rebuilding the clock separate from the incoming stream removes any chance for jitter or timing errors to cause the difference…and I don’t believe there is. The author didn’t mention the equipment.

      • Re-clocking is a vague term that encompasses a variety of methods. A well-designed PLL or asynchronous sample rate converter can significantly reduce jitter, and using a buffer can eliminated entirely. If, however, the DAC in question doesn’t have good jitter immunity, or it’s a single box CD player with inadequate electrical isolation of the transport from the DAC and analog sections, there is a clear path for changes in the operation of the transport to affect the sound quality.

        The reviewer may, indeed, be blowing smoke. But, without knowing the equipment used in the test, his observations are not helpful, and your grounds for disregarding those observations rest on a lot of assumptions.

  • Seems to me I remember back in the day some super ears were cryogenically freezing discs and claiming all those flowery improvements to them too. Something about microscopic alignment of the pits making for a smoother more analog sound. 🙂

  • Not directly related to today’s post, but significant nevertheless: from Cookie’s site:
    Provenance: Pacific Premieres was originally recorded to 9632 PCM (9632 is shorthand for 96kHz, 32-bit (float) sampling). The 9632 WAV files are the original digital file generation received from the artist or label and are not available for sale.

    The DSF, WAV and FLAC files are considered second generation and are conversions made using our proprietary methods.

    • Thanks Alan. There is no such thing as “second generation” digital. Generation implies loss at each transfer or conversion. Digital doesn’t experience loss when sticking with the same specifications. If Cookie’s technique is converting a file from PCM to DSF, then there will be some change in the data stream but it’s not the same thing as “generation” loss. I haven’t looked at the Blue Coast Records site in a while but would like to know more about originally recorded at 96 kHz/32-bits. I’m not aware of very many ADCs that were running 32-bits back in the day.

  • Carlo Lo Raso

    Don’t forget about the tweak that involved marking up the inner and outer edges of a CD with a green marker….It made SUCH a difference! 😉

  • Don Hills

    Was that description of CD manufacturing yours, or was it from the post you were quoting? It contains so many errors about the process that I hardly know where to start…

    • I’m interested in what you would argue with…

  • Don Hills

    I found the article about the glass CD. It’s an interesting concept. I haven’t yet found any details on how they physically produced the pits on the disc surface – engraved, or pressed into a thin plastic layer on the glass, or “burnt” into a photosensitive layer like a CD-R? Also, the glass they are using would be a special order. Most optical glasses have a lower refractive index than polycarbonate, so the glass would need to be thicker to properly focus the laser on the pits. A thicker disc could cause problems with the clamping mechanism.

    Now to the arguments… 🙂

    “The LBR burns away very small pits in the surface of a pristine glass disc…”

    It’s more complex than that. It is a photographic process. The laser “exposes” what will become the “pits” onto a photosensitive layer coated on the disc. “Developing” the layer and etching causes the areas that will become the pits to be etched away. There are a couple of diferent processes in use, but the end result is physical “pits”. I’ll grant that you may have oversimplified rather than be wrong. 🙂

    “However, contrary to the author’s claim that, “Digital data are stored on the CD in ‘pits’ (indentations in the disc) and ‘lands’ (the flat disc surface),” a series of manufacturing steps actually results in exactly the opposite physical arrangement on the surface of the discs that we play. They are bumps NOT “pits”.”

    In all cases, the physical arrangement on the surface of the final disc is a series of pits.
    From a reading point of view it doesn’t matter if the result is “pits” or “bumps”. It’s just that when moulding the final disc, the plastic flows better around the “bumps” on the stamper than it would fill “pits” in the stamper.

    “… the pressing machine where the stamper is slammed up against the material. ”
    The stamper forms one side of a disc-shaped mould, which stands still while liquid plastic is pumped in.
    (Unlike pressing vinyl, where a piece of solid vinyl is squeezed between two hot stampers.)

    “… a thin layer of additional clear polycarbonate is layered on top by dropping a small bead of liquid plastic and spinning the disc rapidly. The disc is then turned over and the disc artwork is silkscreened onto the surface.”

    A thin layer of UV-curing lacquer is used, not polycarbonate.The lacquer is applied to the plated side, which is the same side that is printed, so the disc is not turned over.

    Regarding the way two discs can sound different, it’s pretty well understood that if you use a DAC that is not affected by jitter, the differences disappear. There’s no excuse nowadays for a DAC (separate, or built into a player) that is audibly affected by jitter at any level below that bad enough to cause actual bit errors.

    • Thanks Don, I feel better.

  • Don Hills

    I found a description of the glass CD pressing process.
    A metal stamper is made with the same process as used for polycarbonate CDs. A glass disc is coated with a soft plastic resin and pressed against the stamper. The resin is hardened by UV light. The disc is then plated, coated and printed in the same process as a polycarbonate CD.

    It’s hard to see how this could produce a CD with the better pit geometry etc claimed. Most of the geometry is determined by the quality of the steps prior to pressing.
    – Glass master exposed and etched (pits).
    – Electro-deposit nickel on the glass master and peel to create a metal “father” (bumps).
    – Electro-deposit on the father and peel to create a metal “mother” (pits).
    – Electro-deposit on the mother to create a “son” or stamper (bumps). (Repeat if more stampers needed.)
    – Mould into plastic to create the CD (pits).

  • Also worth noting, neither the pits nor lands are ones and zeroes. It is the transition between them that is read as a one. Whether that transition is pit to land or land to pit. You get zeroes always until a transition occurs.


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