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 “Filters

  • Lin Hong Wong

    Hi, glad you brought this subject up. I’ve been wondering what happens when I play a 96/24 hires downloaded file through a DAC onto my hifi. Surely the pre-amp, amp and/or speakers will filter off frequencies above 20kHz? So why would hires sound different from a CD? Is it just the difference in dynamic range? What about super tweeters?

    Will subharmonics or undertones add to the music that we hear, if the frequencies above 20 kHz are generated by the hifi? Many musical instruments generate such high frequencies and so they sound different when played live versus from a CD. It is notable that Sony has come out with a hifi with response up to 50kHz.

    Would appreciate it if you could address these in Part II. Sorry for the many questions. I have found your blog very educational. Thanks.

    • Admin

      If the source file that you playback is indeed a 96 kHz/24-bit soundfile, it potentially contains frequencies higher than 20 kHz and dynamic range wider than 93 dB (the dynamic range max associated with CDs). However, your pre-amp and amplifier are capable of passing higher than 20 kHz (probably close to 100 kHz). But the quality of your speakers are probably the limiting factor. The dynamic range will come through and you might be able to perceive differences. Super tweeters also help.

      The undertones or subharmonics are not something that I believe matter very much at all. I’ll write further about this.

  • David Gallup

    Mark, this made me laugh: “A fuel filter stops impurities from getting into your carburetor and causing your engine to run rough”. While that is completely correct, there has not been a new car sold with a carburetor in this country for 25 years. You may be a stickler about the terminology for HD Audio, but you missed the biggest contributor to reduced automotive exhaust emissions and improved fuel economy, digital fuel injection.

    As someone who has spent 35 years designing fuel injectors I can’t help pointing out your omission. Just for the record, fuel injection systems require better filtration than the old carburetor. We also have D/A converters though no one speaks of them as such. The digital value for the desired fuel delivery quantity has to be converted into an analog pulse to drive the injector. The injector bears some semblance to a speaker being an electromagnetic or piezoelectric transducer and responsible for the accurate transformation of the electrical signal to the final output. Two different medium but many parallels.

    • Admin

      Ok fine…as a product of the motor city, I admit to being a complete idiot when it comes to the inner workings of an automobile. When I was working on things mechanical, there were carburetors. I found your comments amusing and informative. Thanks.


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