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  • Here is a listing of sites and pointers to references which are of some particular interest to electro-acoustic loudspeaker design, to sound reproduction in small spaces and to listening enjoyment. It also refers to recording, music, amplifiers and other subjects of interest to me. The links are ordered chronologically from oldest to most recent on top, the way I posted them. 
  • DNA and Its Epigenetic Potential, an Antenna for Cosmic Emissions:
    Driving Force in Evolution and Energy Transmission? - PDF


  • Recommended reading
    Here are three books well worth exploring, as you wonder about our place in the universe

  • Bruno Putzeys - of Hypex amps and Kii-3 loudspeaker fame - wrote about MQA on facebook:
    This isn't a prelude to suddenly becoming active on FB but I felt I had to share this.

    Yesterday there was an AES session on mastering for high resolution (whatever that is) whose highlight was a talk about the state of the loudness war, why we're still fighting it and what the final arrival of on-by-default loudness normalisation on streaming services means for mastering. It also contained a two-pronged campaign piece for MQA. During it, every classical misconception and canard about digital audio was trotted out in an amazingly short time. Interaural timing resolution, check. Pictures showing staircase waveforms, check. That old chestnut about the ear beating the Fourier uncertainty (the acoustical equivalent of saying that human observers are able to beat Heisenberg's uncertainty principle), right there.

    At the end of the talk I got up to ask a scathing question and spectacularly fumbled my attack*. So for those who were wondering what I was on about, here goes. A filtering operation is a convolution of two waveforms. One is the impulse response of the filter (aka the "kernel"), the other is the signal.

    A word that high res proponents of any stripe love is "blurring". The convolution point of view shows that as the "kernel" blurs the signal, so the signal blurs the kernel. As Stuart's spectral plots showed, an audio signal is a much smoother waveform than the kernel so in reality guess who's really blurring whom. And if there's no spectral energy left above the noise floor at the frequency where the filter has ring tails, the ring tails are below the noise floor too.

    A second question, which I didn't even get to ask, was about the impulse response of MQA's decimation and upsampling chain as it is shown in the slide presentation. MQA's take on those filters famously allows for aliasing, so how does one even define "the" impulse response of that signal chain when its actual shape depends on when exactly it happens relative to the sampling clock (it's not time invariant). I mentioned this to my friend Bob Katz who countered "but what if there isn't any aliasing" (meaning what if no signal is present in the region that folds down). Well yes, that's the saving grace. The signal filters the kernel rather than vice versa and the shape of the transition band doesn't matter if it is in a region where there is no signal.

    These folk are trying to have their cake and eat it. Either aliasing doesn't matter because there is no signal in the transition band and then the precise shape of the transition band doesn't matter either (ie the ring tails have no conceivable manifestation) or the absence of ring tails is critical because there is signal in that region and then the aliasing will result in audible components that fly in the face of MQA's transparency claims.

    Doesn't that just sound like the arguments DSD folks used to make? The requirement for 100kHz bandwidth was made based on the assumption that content above 20k had an audible impact whereas the supersonic noise was excused on the grounds that it wasn't audible. What gives?

    Meanwhile I'm happy to do speakers. You wouldn't believe how much impact speakers have on replay fidelity.
    * Oh hang on, actually I started by asking if besides speculations about neuroscience and physics they had actual controlled listening trials to back their story up. Bob Stuart replied that all listening tests so far were working experiences with engineers in their studios but that no scientific listening tests have been done so far. That doesn't surprise any of us cynics but it is an astonishing admission from the man himself. Mhm, I can just see the headlines. "No Scientific Tests Were Done, Says MQA Founder".

    My thoughts: Human hearing is a non-linear process of sound perception as can be deduced, for example, from the equal loudness contours. Hearing evolved for survival. High frequency ticks and clicks are instrumental in determining the direction to the location of a potentially threatening source. I wonder if we have hearing acuity for such type of signals that goes beyond the frequency range for steady-state stimulus perception. I doubt that hearing can be fully described in Fourier analyzer terms. If Bob Stuart truly has discovered a new perceptual phenomenon, then he needs to demonstrate it scientifically. Otherwise MQA is just a marketing ploy to resell previously recorded material in a proprietary file format and they are Phishing for Phools. - SL 


    - Interview with 'Esprit Yoga Magazine'

    Skype Satsang with Mooji

    Living in the Joy of Our Natural Being

    Set Your Heart Free - An Introduction to the Invitation


    An Invitation to Freedom

    God Is Your Guru

  • Artificial Accuracy
    The Metrology of Quality, Quantity and Convenience
    Story and Context

  • A story of purpose
    Mark Twain:

    The two most important days of our lives ...

    1 - The day we were born

    2 - The day we found out why

    Hi Siegfried,

    I thought you may be interested in this brief TED Talk if you have not already seen it.
    It describes an experiment looking at what happens in the brain when a subject is tasked with focusing on one of two visual elements (overt attention) compared to when tasked to focus between them (covert attention).

    I would suspect this would have strong parallels with audio stream segregation.

    James Heddle
    Acoustical Consultant

  • Neuroscientist Uri Hasson researches the basis of human communication, and experiments from his lab reveal that even across different languages, our brains show similar activity, or become "aligned," when we hear the same idea or story. This amazing neural mechanism allows us to transmit brain patterns, sharing memories and knowledge.

    "We can communicate because we have a common code that presents meaning," Hasson says.


  • What is so special about vinyl?

    My dear friend, Craig Allison, founder, singer and slide guitar player of a local 'Bourgeois Blues Band', and now selling 2-channel sound at Lavish Hi-Fi in Santa Rosa, wrote to me: 

    Hi Siegfried,

    We had a big vinyl event here last Saturday; absolutely amazing, almost 200 people, about 1/3 of the doctors in Santa Rosa were here.

    We put on a great show, but I remained quizzical as to the outrageous major buzz that manifested unlike any other event we've had. I have preciously dwelt on this 'phenomenon' at some length, and concluded that the distortion family of vinyl is being re-embraced as an antithesis to the sound of highly compressed MP-3.

    Remember, you don't listen to a lot of terrible current pop music, but the masses do.
    But the reaction I picked up obviously went well past this one factor.

    Had a great Facetime chat w/ a brilliant friend of mine in Canada last night, talked about this.
    And then it hit me: the significance of ritual, and what happens when you take it away.
    The public is overjoyed returning to a ritualized recorded music playback.

    As I enjoy certain rituals as well, I understand that the same experience w/o ritual is simply not the same experience at all. I love CD, but there is no palpable ritual involved, and even less using a phone to bluetooth etc. ....

    Yes, Craig, your thoughts resonate strongly with me. 
    We all know that music can touch and move us at a deep level. And going through the preparations for playing a vinyl disc, then sitting down in anticipation, is like opening a perceptual door, paying attention, being ready to receive and to lose one's daily self. Streaming a concert by the Berliner Philharmoniker can have such an effect on me.

    I just started reading: 'Music, The Brain And Ecstasy - How Music Captures Our Imagination' by Robert Jourdain.

  • Dynamic Range: No Quiet = No Loud

  • Music with a Cochlear Implant?

  • Archimago's Musings

  • AmericanRadioHistory.com

    My "Loudspeaker System Design" articles were originally published in Wireless World, 1978, May, June, December.

  • Technology Trends - High Resolution Audio

       HRA-trends.jpg (586973 bytes)     JAES, March, 2017

  • The Art of Listening - from the artist's and producer's perspective

    Chesky Records

  • Room Acoustics for Listening - James Heddle, Acoustical Consultants, Brisbane, Australia - facebook
    ".... Acoustic design targets based on data and parameters derived from single microphone measurements are therefore likely to have inadequacies and may be misleading. Overall this implies our current understanding and models of perceptual processes, including those involved with listening, have significant room for improvement and are likely to more fully develop over time. We should, therefore, be cautious of design based solely on room acoustic parameters given in current international standards (Lokki, 2013)."

  • Fresnel Zones and Spheroids for Room Acoustics - - James Heddle, Acoustical Consultants, Brisbane, Australia - facebook 
    Abstract - The concept of Fresnel Zones arises from considering reflection paths off a surface differing from the direct sound propagation path by some multiple of half a wavelength. The modelling of these zones, and of zones derived using a set time delay, provides useful insights for the design of spaces for listening and communication. This paper gives an overview of analysis using this approach together with some examples and is intended as a companion paper to 'Room Acoustics for Listening'.

  • Loudspeaker Cabinet Diffraction
    The paper by Tore Skogberg illustrates the difficulties in analyzing and predicting diffraction effects. Added to that are the finite dimensions and modal breakup effects of real sources. But it is important to understand the general trends in order to design sensible baffle shapes and to optimize them by acoustic free-space measurements on-axis and around the cabinet. See also My Conversations with Fitz.

  • A Meta-Analysis of High Resolution Audio - Perceptual Evaluation

  • ECMA-407 and Telecommunications in the 21st Century

    InterComms talked to Ecma TC32-TG22's Convenor and Swissaudec's CEO Clemens Par about the 21st century's broadcasting and communication means.
    The pdf of the interview gives an introduction to the ingenious concept and methodology behind the Ecma-407 standard for down-mixing f-channels of audio into g-channels and then transmitting them using currently deployed codec's like AAC or HE-AAC. On the receiving end of the bit-stream transmission the g-channels can be up-mixed again to f-channels or a smaller number of h-channels depending upon the playback setup. 

    The process has higher proven performance than UHD 3D-audio codec's currently under development. See the White Paper: ECMA-407 "Instant HD to UHD Audio".

    Clemens Par gives credit to Rudolf E. Kalman and Guenther Theile in the InterComms publication of: Rationalism versus Empirism - A Crash Course in Invariant Theory.

    Swissaudec exhibited in 'NAB Labs Future Park' at the 2016 NAB Show in Las Vegas.

    I am a personal friend of Clemens Par, having met him first at TMT26 in 2010, where I was mightily impressed by his process for up-mixing a mono audio signal to stereo as if recorded with a MS coincident microphone pair. Since then much more powerful applications have evolved out of Invariant Theory and inverse coding. But it pains me to see how established audio standard setters resist to accept and incorporate the new paradigm.  

    See also Rationalism and swissaudec GmbH below.

  • Reverberation ...and how to remove it
    binaural-listening.jpg (256177 bytes) The Feature Article by Francis Rumsey in the April 2016 issue of the Journal of the Audio Engineering Society ends with a section about THE BENEFITS OF BINAURAL LISTENING IN REVERBERANT CONDITIONS (copy on left).

    Auditory stream segregation is at play when the listening room and the loudspeakers in a proper stereo setup recede from perception and are moved beyond the acoustic horizon of the listener.

  • Floyd Toole:  Room reflections and Human Adaptation for Small Room Acoustics
    Floyd's article in www.audioholics.com discusses hearing in reflective, resonant and reverberant spaces. I find it refreshing to read:

    "Humans evolved while listening in reflective spaces, and are comfortable listening in them. In fact, it is now widely recognized that we perceptually "stream" the sound of the room as separate from the sound of the sources - that is what happens in live performances. A Steinway is a Steinway; only the hall changes. Performance halls generally don’t have room mode problems because they are so large. The parallel situation in sound reproduction is that a good loudspeaker is a good loudspeaker, and its virtues are appreciated in a wide variety of rooms – except for the differences in the bass region."  
    (The differences in the bass region largely disappear when dipolar or cardioid woofers are used. - SL)

    "As an illustration of how much loudspeaker technology has improved over the years, these data on the JBL Pro M2 indicate that whatever one’s opinions of loudspeaker/room interactions were in the era of the UREI, they cannot be the same in the era of the M2, and any similarly “neutral” loudspeaker. Because it is desirable that the direct and reflected sounds resemble each other, the newer loudspeaker has an enormous advantage. Traditions need to be put into context, and some of them relegated to history."
    ("Neutral" ultimately means Constant Directivity over 4
    p space. The M2 represents a step in the right direction, but is still omni-directional at low frequencies and forward directional, though with wide dispersion, at high frequencies. - SL)

    I just wish more speaker designers would take seriously the implications of the highlighted statements above.

    See also a more recent article by Floyd "What do listeners prefer for small room acoustics?"

  • Floyd Toole: The Measurement and Calibration of Sound Reproducing Systems
    In his Paper you find out about traditions and the disappointing state of affairs in professional audio. A discussion of this Open Access AES Paper
    is at the AES Journal Forum

  • Seth Horowitz: The Universal Sense - How Hearing Shapes The Mind
    Here is an easy to read book, written by a neuro-scientist for the general public, which describes the response of the ear/brain perceptual apparatus to sound, to what draws our attention, affects our emotions, our memory and possibly our actions. I highly recommend this book to anyone involved with sound, whether in production, rendering or listening. My loudspeaker designs for creating convincing auditory illusions in ordinary rooms are intentionally based on evolutionary hearing processes as described by Horowitz.

  • Optimizing the directivity index of a 2-way loudspeaker
    Diego Ivars Morón's Master's Thesis at the Norwegian University of Science and Technology deals with different approaches to obtain very wide dispersion from the tweeter section of an otherwise omni-directional loudspeaker.

  • Acoustic power radiation from loudspeaker cabinets
    Conventional box loudspeakers very often suffer from spurious sound radiation, which is caused by the mechanical vibration energy of the drivers being transmitted into the cabinet and exciting the cabinet walls to vibrate at certain panel resonance modes. Furthermore, the high sound pressure levels inside the cabinet can excite panel modes. Since the cabinet's radiating surface areas are usually much larger than the driver cone area even relatively small panel excursions can lead to
    significant spurious acoustic output. Depending upon the cabinet construction the output might even be larger at certain frequencies than the desired output from the driver. In addition, air borne acoustic energy inside the cabinet, which is very difficult to absorb and to turn into heat will escape via the thin cone material of the driver and can color the sound. These problems taken together and combined with a sub-optimum radiation pattern generates the generic box loudspeaker sound. Conversely, an acoustically small, open-baffle (dipole) loudspeaker with its minimal baffle area and no box enclosure is largely free of spurious emission problems. 
        The Open Access AES paper "Predicting the Acoustic Power Radiation from Loudspeaker Cabinets: a Numerically Efficient Approach" deals with acoustic radiation due to structure borne vibration energy in a highly braced cabinet. It is an interesting read and shows how much attention must be given to cabinet details to minimize spurious emissions.

  • Hauptmikrofon.de
    The Hauptmikrofon.de website was updated by Helmut Wittek (Schoeps) and relaunched in 2015 with an emphasis now on 3D audio. Unlike WFS or Ambisonic approaches that aim for exact physical reconstruction of the recorded soundfield here are microphone arrangements described, which exploit the psychoacoustics of hearing and Gestalt recognition as originally described in the groundbreaking work by Guenther Theile. While the emphasis is on microphones and their characteristics on the sound recording side, little is said about loudspeakers and rooms, which after all are the other half of the story on the sound rendering side. As far as I know conventional box loudspeakers have been used to assess the recording techniques. This can only be justified by their popularity. But if optimum 3D rendering is the goal then also loudspeakers, their characteristics and setup, and the room have to be revisited!
    3D Audio Natural Recording -
    Microphone Techniques for 2.0 and 5.1 Ambience Recordings
    ORTF-3D Microphone technique for 3D ambience recording

  • Rationalism versus Empirism
    This publication by Clemens Par of swissaudec in Issue 25 of InterComms is a tribute to Professor Rudolf Kalman and was inspired by conversations between them. It is also a tribute to Guenther Theile's groundbreaking work in auditory spatial perception. Their mathematical contributions to systems and invariant theory combined with new understanding of cerebral spatial hearing processes have led to new forms of audio coding as now standardized in ECMA-407 for UHD 3D audio.
    I am pleased to know that Clemens considered the PLUTO's design and phantom imaging, which he heard at TMT26 in 2010, as proof for his then new, invariant method of upmixing from mono to stereo. See also below:
    swissaudec GmbH
    Ecma publishes the world's first 3Daudio standard: ECMA-407

  • Music Theory & MIDI Encoding
    In this YouTube video Charlie Gillingham (2015 NuPIC Hackathon) talks about the challenges in machine decoding MIDI files, whereas the human brain's Hierarchical Temporal Memory