Dr. AIX's POSTS TECH TALK — 02 May 2014

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There is an article over at Digital Trends entitled, “Everything You Need To Know About High-Resolution Audio, The Future Of Music” written by Caleb Denison that takes a look at the emerging world of high-resolution audio. There’s a large image of three Pono players, a chart of fidelity levels and a picture of a set of Sennheiser headphones.

The author lays out the article with a little backgrounder followed by a series of questions pertaining to high-resolution audio. His outline is good but the details in each section stray pretty far from the facts.

I have to wonder whether a journalist with his background as a “professional musician, amateur chef and A/V electronics guru” actually qualifies him to explain the inner working of PCM audio and the whole subject matter at hand. Perhaps it’s just the definitive nature of his title that tweaked me this morning.

The first section “What does the term ‘high-res audio’ mean?” might seem simple but as I’ve written previously, it’s proving very difficult to nail down. The term high-resolution audio has been around for at least 15 years and is not a new term to those paying attention to this area. It’s true that HD-Audio co-existed with HiRes Audio for most of that time, but now it seems that consensus is tilting towards high-resolution audio. I wrote about the advantages of HD-Audio…but I lost that battle.

The second paragraph begins, “While high-res audio is really a very broad term that could apply to any kind of high-quality sound, it has become popular to use it to refer specifically to high-quality digital music files.” High-resolution audio can ONLY apply to digital files that have a minimum specification. When we consider high-quality analog sound the term “resolution” doesn’t enter into the picture. Analog tapes or vinyl LPs don’t have “resolution” because they store information without sampling and dividing continuously variable electronic signals into discrete parts. These formats certainly have fidelity specifications but it is incorrect to consider them “high-res audio”.

The author breezes through a brief history of audio quality (vinyl LPs still rule the top of the fidelity hill), before proceeding to a section on “How do you measure music quality?” I think he’s strayed away from his central subject and migrated over to music criticism. He would be better advised to title this section, “How do you measure the fidelity of recorded music?” Otherwise we’d be arguing about whether Bach’s “Italian Concerto” is “better” than Chopin’s “Ballade in gm”…which is a useless exercise.

This is followed by an explanation of “sampling rate”. Here’s the paragraph:

“Sampling rate is the number of times a sample (a sonic picture, if you will) is taken of an audio signal per second. The more times you sample an audio signal, the more detail you end up with. Sampling an audio signal is like shooting a video of a fast-moving object. The higher the frame rate (sampling rate) the more depth and detail you can capture and the smoother the end product is going to be. Say you’re shooting a video of a cheetah running across the savannah. At 24 frames per second, you will still be able to tell it’s a cheetah, but the details are lost in a blur. At 1000 frames per second, though, you might be able to see all of the cheetah’s whiskers, count its spots and notice its tail is slightly kinked toward the end. Again, it’s all about heightened detail.”

This explanation is not even close to being accurate. It sounds like a line from a sales brochure for the new 384 kHz DACs that are starting to come on the market. Increasing the sampling rate doesn’t provide you with “more or heightened detail” unless you define the addition of higher frequencies to mean “more detail”. The rest of the paragraph switches over to a comparison to film/video with its frames per second capture scheme. Which is where the author steps completely off the track.

Sampling audio is not analogous to using individual frames to capture motion on film. You don’t get “more depth and detail” at 1000 fps vs. 24 fps. You get a lot less strobing, the ability to do great slow motion and will need a giant reel of film! Both system are using sampling but the output is fundamentally different.

The sample rate of a PCM digital system functions according to the rules laid down by the Shannon-Nyquist theorem. We need a sample rate that is at least and at most twice the frequency of the highest component in the signal to be converted. That’s the reality. So if we present a band limited 20 Hz – 20kHz signal to our ADC, we have to have a sampling rate of 40 kHz…and no more. It’s better for the filtering if we push that out a few thousand Hz to around 44.1 kHz. And, of course, I’m an advocate of going to the next multiple out and using 96 kHz as the high-resolution sample rate.

I’ll continue tomorrow with part II.

My point in writing today’s post is less about rehashing the ideas behind PCM audio encoding and more about why readers are being confused by inaccurate articles…especially ones that tell this is everything I need to know.

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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.

(20) Readers Comments

  1. It is reallly a pity and disgusting when a reviewer like Mr. Jonathan Valin from The Absolute Sound Magazine put a derogatory remark at the magazine site on Mr. Waldrep showroom at the last Axpona Chicago 2014. His words:

    “Finally, in a show in which sonics were definitely a mixed bag, I want to note a particularly egregious presentation. After haranguing showgoers about “high-definition” audio (which, apparently, doesn’t include anything sourced from analog), AIX’s Mark Waldrep proceeded to turn a near-half-million-dollar German Physik loudspeaker system, the $475k Emperor II, into a laughing stock with one of his high-res multichannel tapes. The sound on female voice was incredibly big, ill focused, bright, and unpleasant.”

    That comment demonstrates the ill character of said man who doesn’t seem to know anything about HiDef Audio. He even does not know that there is no HiDef on analog media. How can that man be a reviewer?

    • Ronaldo…that’s for the heads up on this one. I wrote a response on the TAS site…but it is very surprising that a writer working for one of the most prestigious trade magazines would issue a comment like that. Here’s my comment for those that might want to steer clear of the TAS site:

      “Jonathan, this is certainly your soap box to voice your opinions about the Madison ballroom at AXPONA and the quality of the sound produced from the recordings that I’ve produced but I can’t imagine how you could come to the “opinion” that you published when the vast majority of other writers and visitors came to completely different conclusions.

      After all. these are the same recordings that your own colleague Andrew Quint called, “…quite simply the most realistic and involving instance of recorded sound I can recall, from any source format. Mark Waldrep knows what he’s doing.”

      First, I should politely point out that I wasn’t presenting “multichannel tapes” but rather a custom made High-Resolution demonstration Blu-ray disc…primarily because high-resolution audio, multichannel audio can’t be delivered in a format that is limited to around 60 dB of dynamic range…analog tape (but maybe you didn’t know that analog tapes only reach about 10-12 bits of dynamic range in PCM terms).

      You can define HRA any way you like, but the CEA, NARAS and AES committee’s that I participate in on my side on this issue (I believe your editor Robert Harley is also keenly aware that older analog recordings are not really high-resolution) as is the current president of the AES, Harman’s Dr. Sean Olive. I believe I’m going to go with Dr. Olive on this one.

      I would finish with a few comments that John Hamm, the CEO of Pono and AXPONA keynote speaker made to me after I played a spectacular track featuring a well know female voice, some Dave Mason and John Gorka. He was absolutely astounded with the warmth, openness, emotion and fidelity of the track and insisted that I provide him a disc so that he could share it with Neil Young as a demonstration of what’s possible with high-resolution equipment.

      I also received this email from a visitor to our room, “We attended AXPONA last week. My wife bought “Primavera” [Note: The selection with the female voice mentioned in your post] in response to your excellent presentation. I also visited your room at AXPONA 2013 several times last year during the show. Both years AIX’s room was among the very best at the show.”

      You are certainly entitled to prefer the fidelity of older analog formats or prefer the sound of vinyl LPs or tape but completely dismissing the presentation in the Madison room with such nastiness and negativity is uncalled for and I would think beneath the standards that TAS tries to live up to.

      • Interesting. Mr. Valin singled you out because he disagreed with your opinion. Nasty man. I was glad to see a number of people take offense of his unprofessional conduct.

  2. I love your newsletter ..thanks.
    Some advice please. I have 200 CD recorded in FLAC on my PC previously using Squuzebox as a playback thru WMP. Squuzebox is no longer supported & Im thinking of changing from PC to MAC as we all have apple iphones , timemachine & their wi-fi extenders that we use with Airplay.
    What the best way to store my files if I can move to a MAC,(does conversion lose all the tags) is their any way of maintaining fidelity when streaming by WIFI, & what the go with playing from my mac to my AMP..where does Amarra fit in, will I have to rerecord my music on the mac I am yet to bye (any suggestions here re music)
    While I understand its always better to play my CD on my player, Id like to make my music a little more accessable. Also any suggestions on a few our your recomended best music recordings as a starter.
    Also any suggestions on better music streaming stations

    ThanksRegards from a total amateur Mike

    • I will have to response by way of a post or two. Be patient and I’ll get you the answers you need.

      • I will be glad to hear your thoughts on this, Mark. I went from WMA lossless in the PC world to ALAC in Mac. Unfortunately, FLAC doesn’t play natively on Mac and ALAC isn’t exactly universal like FLAC. To Mike: the conversion program that I use is XLD which keeps the tags in place and support almost all formats. It is free, but we should support the programmer because he is alway updating it.

  3. Hello Professor,
    I am sorry to hear that those “old-fashioned” audiophiles still see a devil in everything except their so well-loved vinyl.
    I can only imagine how that live comparison went with Gorka playing and then re-playing his songs from Disk. Suck it narrow-minders!!! I own by now 18 of your DVD-A’s and many I enjoy. I mostly like Vantage Point. Two of my favorite musicians are on the recording and the songs are all great. Best so far among all the DVD-A’s. I just happen to listen to Geissman’s recording and I wonder where are the frequencies above 6 kHz? I had to use the foobar equalizer to crank up the frequencies above 6 kHz mainly at 8 kHz 10db??? No such thing is necessary on any other CD/DVD-A I own and certainly none of your wonderful DVD-A’s. What happened? Even the cymbals sound dead.
    Cheers from a supporter

    • I’ll have to go back and check on the Grant Geissman recording. I’ve never had anyone say that it was lacking in high frequency information. It is true that it was not recorded in the normal venue we use in downtown Los Angeles. We did it in a regular studio at the request of Grant. I’ve always been averse to using a commercial type facility to get the sound I prefer…but so it goes.

  4. I think the article in Digital Trends was pretty good and I don’t accept much of the criticism you leveled at it.

    Yes his way of explaining word lengths and sampling rates may not have been very accurate to someone who knows what these things are but that is not who the article was aimed at. A completely accurate and sensible description might well have frightened readers of and that is not what is needed now. In the NAIM audio streaming forums many of the bloggers there still believe that a digital signal must be degraded during transmission or that NAIM server device is much better than any other hard disk solution (quality-wise that is) or that lossless compression does take stuff away. These are people who have taken the plunge already into High Res and spent serious dosh on it.

    Also he did not say that vinyl was top of the quality tree as a statement of fact. For a start it cannot be denied that in terms of sound quality vinyl is vastly superior to 8-track cassettes or compact cassettes or mp3 files – can it? The only bone of contention is whether or not it is superior to CD and to say NO it isn’t is not a valid argument either. Some people say yes it is others say no it isn’t. The problem with vinyl of course, is that you need a top quality front-end to really hear it well and it is much less convenient and durable than CDs. His actual comment on the Vinyl Vs CD debate was “but some argued it lacked the organic, natural sound of analog formats.” How exactly is that stating “vinyl LPs still rule the top of the fidelity hill”?

    The final point I would like to make is that I really don’t care what they want to call 24bit digital audio, what matters to me is that we are now hearing digital music that sounds really very good. What worries me is that the software will carry on being hard to come by and expensive, but no they can call it what they want. I could not give a monkeys on what they call it – Sorry.

    • Bill, it bothers me when someone writes a “comprehensive” piece that has inaccurate information or analogies in it.

      You are correct that he didn’t state that vinyl LPs are the best…he mentioned that many still believe it. But I start to move away from you in the rest of the paragraph. Vinyl LPs are not “vastly superior” to some of the formats you mentioned. The problem with vinyl LPs is that they are derived from analog tapes that have limited dynamic range…and the vinyl mastering process changes the mixes to suit the format (folding low frequencies to mono and juicing the high frequencies). Vinyl can sound wonderful but the actual potential fidelity of the format is much less than CDs. We should have to compare the two…like what you like for the reasons of the music.

      • I said that vinyl was superior to 8 track cassettes, compact cassettes and mp3 files I did NOT say superior to CD, I did not want to get into that argument. You have your view and I have mine. So which of the 3 formats I mentioned do you think beats vinyl? I have experience of all three and I am horrified that you think they (or at least one of them) sounds better than vinyl.

        • The requirements for vinyl LPs mean that low frequencies can’t be maintained in stereo and that high frequencies are skewed by the RIAA curve…which are not required for any of the other formats. I would also put my 320 MP3 files up against a piece of vinyl any day of the week…they are virtually CD quality, which bests vinyl in terms of delivering what left the mixing studio.

          • “they are virtually CD quality, which bests vinyl in terms of delivering what left the mixing studio.” – you cannot state this as a fact, this is your opinion and is not shared by everyone.

            But again you go off the point I was making about the article which you criticised so much for putting LP at the top of the quality pile. That was a statement he never made in the article and it is my personal belief that if you criticise someone for making a statement you don’t agree with t then they should have actually made the statement in the first place.

            But you seem unwilling to comment on this.

            Just call me old-fashioned!

          • Bill, I acknowledged in my reply that he didn’t say LP was the ultimate. A 320 kbps MP3 file delivers more accuracy to a source file than a piece of vinyl…and it doesn’t fold the bass. The high end would be the only compromise…you pick.

  5. Hi Mark,
    Given that you’ve stated this:
    “The sample rate of a PCM digital system functions according to the rules laid down by the Shannon-Nyquist theorem. We need a sample rate that is at least and at most twice the frequency of the highest component in the signal to be converted. That’s the reality. So if we present a band limited 20 Hz – 20kHz signal to our ADC, we have to have a sampling rate of 40 kHz…and no more. It’s better for the filtering if we push that out a few thousand Hz to around 44.1 kHz. And, of course, I’m an advocate of going to the next multiple out and using 96 kHz as the high-resolution sample rate.”

    Interesting. Nyquist theory simply captures turning points of the frequency in question and uses inverse sine functions to build up the waveform, it’s telegraph theory dating back to the turn of the 20th century, do you think we might be missing something? I’m assuming you teach this as you alluded to this in the interview.

    • Not sure what the question is…yes, the Nyquist Theorem has been around for over 100 years but it is still true. In an audio sampling system, we need twice the highest frequency as the sampling rate to recreate exactly the signal that was originally sampled. That’s the situation with PCM audio.

      • The point I’m getting at is that the waveform is being built from the ground up, using the turning points of that waveform, rather than copied (as with an analogue recording) do you think, using just above twice the maximum frequency can give you an exact replica of that waveform?

        • Dave, that’s what the Theorem states…that is possible to get 100% of the original back after the reconstruction. Of course, this is the theory…in practice we have to have great clocks and converters with terrific filters. And we do.

  6. I think it’s sad that someone could be so bereft of any originality of his own that he would choose to spend an entire post leeching off and attacking someone else’s article — an article which, as anyone with reasonable intelligence should understand, was designed not to appeal to or inform audio elitists like yourself, but novices who have been confused on a difficult subject.

    Here you are, spouting about the Nyquist theorem and MP3 superiority over vinyl like you’re a college professor giving a lecture, without even covering the importance of lossless compression, or bit depth, the latter of which is one of the most fundamental facets that makes high res audio superior to CD-quality resolution. You’re so desperate for approval and a feeling of superiority on the subject that you have to question whether the original author is or is not a “musician.” Give me a break, dude.

    Anyone with a music tech background knows the fundamental differences of video and audio when it comes to resolution rates. It’s an analogy for a reason: not because the two subjects match up perfectly, but because it might help a novice get a grasp on an esoteric and difficult subject. Instead of writing a tirade attacking another author who’s trying to promote better sounding music, why don’t you come up with something useful and original to say?

    P.S. As Dave pointed out, if you believe that the capture of only the peak and trough of a wave is the best we can do to reproduce the true authenticity of analog sound in the 21st century, you obviously need to go back to school, professor.

    • Ryan…I am a college professor and I do teach this stuff. The video to audio analogy is commonly used but has no relevance with regards to resolution in audio. It is completely incorrect. Increasing the number and density of pixels bears no relation to more accurate representations of an audio waveform and doesn’t give any insight into the correct meaning of resolution.

      Your Post Script tells it all…yes, two samples on a single cycle of a waveform (per Nyquist and Shannon) does give you enough information to reproduce 100% of the original waveform…that’s what the theorem says. If you want to describe your model of sample theory, I’m open to hearing it.

      Have a good day.

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