Dr. AIX's POSTS — 07 August 2015

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First things first, I continue to read headlines and other references to “high-res audio” when in fact, the author means to say “high-res music”. Remember that the DEG and major labels decided it would be less confusing to have TWO names and TWO logos for “high-res” experiences. So yesterdays discussion about how Amir has without doubt shown that “high-res audio is legit” besides being untrue also used the wrong terminology. High-resolution audio has already been proven. The term and associated logo refer to hardware that is capable of capturing and reproducing frequencies up to 40 kHz and dynamics of 130+ dB. Although, it is difficult to find equipment that can handle the very stringent requirements originally proposed by Sony…it can be done. We equipped a room that met these requirements at the AXPONA show back in April. Benchmark, Revel, DH Labs, and Dolby Labs collaborated on a setup that one attendee called, “clearly the best sound of the show”.

You may have noticed that I routinely use “high-res audio/music” to be safe. It’s unfortunate that I have to fold both terms into a single group, especially since they don’t share the same requirements, but what can you do? I haven’t seen the “hi-res music” logo used much yet, but I’m sure it’s coming.

All of the buzz following Michael Lavorgna’s article at Audiostream was quite a surprise to me. I haven’t followed any of the recent discussion going on at WBF, but I knew that Amir was claiming victory in the battle of “hi-res” perceptibility…by listening to a high quality recording of a set of keys! A recording that had been subjected to at least two sample rate conversions. I’m OK with a serious ABX test…I resist the “emo” type research that talks about “low level” details and other subjective non-measures.

So what would a real test be like. What method would I suggest…what procedures and results would I have to see to be convinced that everything I’ve been doing for the past 15 years means something. I can’t and won’t worry about the statistical methodologies and any of the other things that advocates on both sides of the issue quibble about. Here’s my approach:

1. Use only music recording that have been recorded using the highest quality equipment from microphones to a PCM digital recorder running at 96 kHz/24-bits.

2. Make sure that the studio or recording venue has an extremely low noise floor.

3. The performances music include instruments that have large amount of ultrasonic partials and the compositions/tunes must have extreme dynamics…both transient and gradual.

4. Passively split the outputs of the microphone preamps and send one to an ADC converter running at 96 kHz and the other to an identical ADC at 44.1 kHz. The two converters should be of the highest quality and calibrated.

5. Playback the two recorded streams through identical DACs into the ABX switcher, which should be balanced and completely noiseless when switched. Allow the person being tested to listen to each stream as long as they like and allow them to switch back and forth at will. They can choose the volume of the playback and modify it, if they prefer.

6. Make sure that the entire signal path is capable of achieving the hi-res audio requirements. This means very high-end speakers, extremely quiet and dynamic power amps, and high quality DACs. The power should be monitored and regulated.

The testing procedure would be explained to the participants (one at a time) by an uninterested third party. Participants would be able select A or B or “I don’t know”.

To be continued…

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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.

(6) Readers Comments

  1. “The term and associated logo refer to hardware that is capable of capturing and reproducing frequencies up to 40 kHz and dynamics of 130+ dB.”

    Mark, I do have a question on the reproduction of this spec
    As I do the math on the total SPL for the system you had at AXPONA equals
    (5) Benchmark AHB 480 watts into 6 ohms in mono bridged mode
    (5( Revel Salon2 86.4 dB @ 1 watt 6 ohms
    would deliver 118 dB max at a distance of 6 feet

    You might get close with the JBL horns you have in the studio but not with the Revels. Actually I see a lot of smoke coming from either the Revels or Benchmarks long before the AHB2 started to deliver 480 watts continuous. LOL
    130 dB in room is very hard to do, and highly dangerous to your hearing health in any case.

    • This is the potential of a system…not necessarily the reality.

  2. Dear Mark,

    Regarding your article I agree with all aspects of testing using ABX comparison for detecting High Resolution Audio you proposed, but it fails regarding the room extreme low floor noise. It is very difficult, almost impossible, to get a floor noise below 25dB in our home environment. So, in practical terms, the required dynamics of 130dB+ is not reached, because of that floor noise. We can get at the most a net 100 dB S/N that is almost the limits of CD specification. Therefore, summing the limits of our audio hearing and the limits of our audio environment I believe to be impossible to hear a difference between HRA and non HRA Audio in a ABX comparison, using loudspeakers of highest quality. That is for loudspeakers and does not apply for headphones. For over ear closed headphones of highest quality (15Hz to 50KHz) used by a person who has super hearing audio frequency limits, it is perfectly possible to determine which is the source, HRA or non HRA. That excludes me at 69 years old, because my measured hearing thresholds are 15Hz to 16KHz at the best. I take this opportunity to thank you for you very instructive and straightforward article.

    • I agree…creating a test for HRA will be very challenging and the results…regardless of which way they go…are meaningless for the average consumer. What’s the point, right?

  3. Dear Mark,

    Will you attend the next Rocky Mountain Audio Festival to be held in Denver, CO, beginning October 2nd ?

    All the best.

    • I’m hoping to….it depends on whether the organizers include me in a panel or seminar.

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