Dr. AIX's POSTS — 25 June 2013

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There is a specification document that was produced by the developers of the compact disc back in 1982 called the Redbook (there have been lots of other colors added to the spectrum of colored specification documents but this was the first!). The Redbook provides detailed information on both the physical and electrical characteristics of CDs. If you wanted to get into the CD business as a replicator or a Digital Audio Workstation software house, you had to purchase a copy of the Redbook specification for $5000…and yes, I did get a copy (although without the huge cost!)

It made for very interesting reading. The physical parameters are laid out in a chapter so that people that manufacture stamping lines would know how much polycarbonate to inject into a CD mold and optical drives designers would know how big to make their trays. The pit size and density, mastering requirements, reflectivity of the aluminum layer and the procedures for making stampers were all contained in the Redbook specification. It is the Bible for compact discs, period.

My interest was in the data structure of the discs. There are 1/75 of a second blocks that are used to identify and locate individual locations on the disc for Tracks and Indexes. There are spaces at the start of every track before the start of the first index that are called “pre-gaps” and lots of other boring details about the structure of the discs that matter to someone. For me, I wanted to be able to tuck computer data in with the music data without a standard CD finding and trying to play the data as sound. This was a major issue back in the late 90s and was called the “track 1” problem. I’ll write a whole post about that adventure at a later time…but I was the first to make a disc that solved the issue.

The electrical characteristics were also spelled out in the Redbook. The coding scheme for the data words and the sample rate were established after some wrangling between the Japanese engineers and other electrical engineering professionals. They talked about using only 14-bit words but thankfully settled on 16-bits. The sample rate of 44.1 kHz was somewhat new to audio at the time. It’s a derivative or the video rate 44.056 kHz, which was used on the first commercially available digital audio recording system…the heralded Sony F1 processors. They took care of the audio conversion (AD and DA) and sent video bandwidth signals to a conventional beta or VHS video machine. I have lots of these tapes in my archives and I even have a SONY 601 (the AC powered component version of the F1). Now all I have to do is find a functioning Sony Beta machine…that’s the real challenge.

Anyway, the world was introduced to an audio format in the fall of 1982 with the arrival of the first Sony CD Player…the CD-101. The machine AND all subsequent machines have been built to the Redbook specification. This means that the best they can muster in terms of playback fidelity is 16-bits at 44.1 kHz sample rate. There is nothing else they can do!

HDCD did create converters and machines that would encode and decode a couple of extra bits worth of data in the least significant bits of the 16-bit linear digital words…and it worked. But it required special equipment…outside of the Redbook specification.

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About Author

Dr. AIX

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.

(1) Reader Comment

  1. I looked into HDCD a while back and decided that its process is analogous to Dolby B or C NR for tape… but vastly more refined and with completely different technology. But in essence, it seems to involve dynamically compressing low level information prior to disc production, then reversing it using the HDCD playback circuit in the consumer’s player. Maybe after reading Part II, I will know if I was on the right track. 🙂

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