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.

4 thoughts on “Return From Oz

  • Brian Langevin

    Hi Mark,

    I am listening to Michael Fremer on Scott Wilkinson’s Home Theater Geeks podcast # 215. I just heard Michael say that there is information on vinyl going up to 50kHz and above. The discussion starts at about 18:30 of the show. He also mentions something about a pilot tone on vinyl used for quadraphonic recordings at 50kHz. After hearing this my question is, does this mean there is anything meaningful on the vinyl above 20kHz or is this a mischaracterization of what he has “seen” in a spectral analysis? It would appear to me that not all the components in the analog chain are capable of recording or playback of these frequencies. I guess in the case of quad it would be possible to superimpose a 50kHz tone on the music but I don’t know that for certain.

    Thanks and keep up the informative post.

    Best regards,


    • Michael is a very knowledgeable gentleman about vinyl but I believe he’s misinformed on the practical aspects of record production. I’ve talked about this previously but let me give you the quick answer. Is it possible for a 50 kHz tone to exist on a piece of vinyl spinning at 33 1/3 RPM? Maybe. Does it actually happen in the world of record production and distribution? No. Recording engineers are not recording with microphones that have the ability to capture anything above around 20-30 kHz…especially back in the “good old analog tape days”. And the analog 24-track 2″ tape machines didn’t record frequencies much beyond 30 kHz…and the levels were down considerably at that frequency. All of the subsequent production stages (mixing, mastering etc) reduced any chance that a 50 kHz tone would ever make it to a replicated piece of vinyl. So while under laboratory conditions, Michael might be safe to make that claim…in reality it’s a pipedream.

      The pilot tone in quad is another misrepresentation. Yes, there was a matrixed system used to capture 4 discrete channels on a stereo format but the level of the pilot tone was way down there in amplitude.

      Vinyl LPs cannot deliver the accuracy, the dynamics, and the frequencies of a live performance. People might rave about the sound but it’s nothing like a well made PCM high-resolution recording or even a well done CD!

  • Seems dynamic compression is going strong in live concerts too. Went to a Peter Frampton & Doobie Brothers concert last night in Atlanta.

    The sound from Frampton’s band was decent. GREAT performance, but about what you’d expect for concert SQ.

    The sound for the Doobie Brothers was another story. The DB sound guys heavily compressed/limited the signals from all sources and then drove the speakers to the low end of distortion. The overall sound was very “hard” with vocals very “crunchy”. I found it difficult to understand some of the very well-known lyrics, but the crowd seemed to love the “modern” sound. Pretty much ruined a potentially good show.

    • Dynamic compression is everywhere. It’s a tool that has become a fixture in almost all music and sound reproduction.


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