Published On: August 17, 2020

Acoustic Modeling Could Give Us the Sound of High-End Gear Without the High-End Cost

Published On: August 17, 2020
Last Updated on: October 31, 2020
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Acoustic Modeling Could Give Us the Sound of High-End Gear Without the High-End Cost

Dr. Mark Waldrep explores the possibility of using acoustic modeling to recreate the sonic characteristics of the gear we all chase after.

Acoustic Modeling Could Give Us the Sound of High-End Gear Without the High-End Cost

  • Mark Waldrep, Ph.D. is the founder, president, and chief engineer at AIX Records, an LA-based specialty record company founded in 2000. He has written extensively on audio production and new media, been a regular columnist for eMedia magazine, been featured several times in the recording industry’s standard periodical MIX magazine, and has given the keynote at the AES (Audio Engineering Society) conference in Bogota, Columbia.
    Mark is an active member of The Recording Academy (NARAS) and the Audio Engineering Society (AES). He has been on the faculty of CSU Dominguez Hills in Southern California for over 20 years, where he heads the university’s Audio Recording program.

I'm a musician. Or at least I used to be. I haven't played much in the past 20 years, but I still have my trusty Martin D-18 acoustic six-string guitar, which I purchased new at the Ann Arbor Folklore Center in 1971 for $371 (a price I can confirm because I still have the original receipt!). In the intervening years, I acquired a couple of other guitars, including a Fender Stratocaster made in the United States. When I purchased my Strat, I also needed an amplifier. I wanted one that would allow me to explore lots of different sounds, be compact enough to tuck in a corner of my studio, and didn't cost a lot.

As a recording engineer and record producer, I know how carefully professional guitarists choose the equipment they use to produce their individual sounds. Albert Lee will only play his signature Music Man electric guitar through a Lexicon PCM 42 digital delay line -- other delay lines will not do. He owns several of these vintage devices. And studio and Supertramp guitarist Carl Verheyen was not joking when he told me during the interview for his Collector's Edition DVD that his sound depends on using reverb and delay: "I simply cannot play without them." From instruments to cables and processors to amplifiers, musicians of this caliber define themselves by their sound. And they spare no expense trying to achieve it. Sounds familiar, right?

Years ago, I watched guitar virtuoso Eric Johnson check out a mid-1960s original Fender Twin Reverb amp at a guitar show in Dallas. Eric played on my ill-fated Jennifer Warnes album many years ago and is one of the most detail-oriented musicians I've ever had the pleasure to record. These musicians have the ears and resources to seek out and purchase any piece of equipment their hearts desire. Carl has a Marshall Stack for his huge rock sound and other guitars and amplifiers when he wants a jazzier tone. He probably owns a few dozen guitars and as many amplifiers.

But what are the rest of us supposed to do? I don't want or need a different amplifier for every style of music I like to play. I want a single amplifier that can replicate the sound of Carl's Marshall stack or Eric's vintage Fender Twin in a single unit. What to do?

Acoustic Modeling

The answer is acoustic modeling. It turns out that in this digital age, clever electrical engineers and innovative programmers have created systems capable of replicating the sound of any analog piece of equipment -- including guitar amplifiers, vintage signal processors, reel-to-reel tape decks, and high-end HiFi gear. Using massively powerful -- and inexpensive -- digital signal processors, it' s possible to design hardware and software that can measure and replicate the acoustic energy that reaches our ears from any analog component, cable, or speaker.

This simple idea is often overlooked as we strive to find better and better sound -- the so-called absolute sound. We tend to focus on the equipment, the cables, formats, sample rates, word lengths, and other factors. At the end of the day, all that matters are the acoustic waves that reaches our ear drums. The fidelity we experience is completely contained in the areas of compaction and rarefaction of the molecules of air reaching our ears. Everything!

I got thinking about the magic of acoustic modeling and its potential application to high-end audio after reading yet another ridiculous review of a "budget" line of RCA interconnects, speaker cables, and power cords on another audiophile website from a well-known cable manufacturer. Budget in this case means around $600 for a one-meter RCA cable! Whenever you read reviews with glowing descriptions like "sound that is coherent and precise," "stage presence, and microdynamic precision," or "makes systems sound coherent and entertaining," find another source of information about high-end audio systems. I recognize personal taste and aesthetic choice are major factors in our hobby, but they must take a backseat to science, engineering, and technology -- or at least they should. What technical specification are we supposed to use to measure "microdynamic precision"? Come on. We deserve better.

A Mighty Morphing Guitar Amplifier

Getting back to my search for a suitable guitar amplifier, I was introduced to the Line 6 musical instrument company during a visit to my local music store. The owner of shop turned me on to Line 6, a very innovative company founded in 1996 by Marcus Ryle, a former student at CSU Dominguez Hills (the university where I currently teach audio engineering). The company operates out of Calabasas, California and has been so successful that Yamaha bought them.


Marcus had the brilliant idea of carefully analyzing "iconic" guitar amplifiers and then designing digital algorithms that could replicate the analog signal path, circuitry, and sound of the amplifier in question. I actually had the chance to visit their facility and was given a tour by Marcus many years ago. He took me in the "amplifier" studio where they had every make and model of the best guitar amplifiers ever produced -- vintage and modern designs. The Line 6 engineering team dissected every circuit and recreated the analog signal path using digital processors and software. And it worked! My little Spider amplifier has a rotary knob that can change the sound from a Marshall stack to a Fender Twin with the twist of a knob. Other knobs and switches allow the user to fine tune or adjust individual parameters of a basic sound. I can go from "thunder crunch" distortion to a "twangy country" sound instantly.

Line_6_Amp_Farm.jpgMy hard-core guitar playing son was unconvinced that anything but an analog amp could deliver his sound, so he purchased a very expensive and large Mesa Boogie amplifier and speaker cabinet. It didn't take too long before he realized that hauling that behemoth up and down stairs and getting it in and out of his car wasn't going to cut it. He ultimately opted for a Line 6 amplifier and has never looked back.

And it's not just analog guitar amplifiers that have been replaced by digital modeling. Most commercial recordings are recorded and mixed using Digital Audio Workstations (DAWs) like Pro Tools, Logic, or Nuendo. And virtually all of the processing -- equalization, reverb, dynamics processing like compression and limiting, etc. -- that used to be done with analog outboard gear has been replaced with digital plug-ins that model their analog predecessors. For example, the fabled and "must have" UREI 1176 compressor/limiter now exists in code along with just about every other vintage piece of signal processing gear. I sold my 1176 a couple of years ago. There are also digital plug-ins that do things that can only happen in the digital domain.

Virtual instruments have received the same treatment. DAWs and other digital music generators can very accurately recreate the sound of any acoustic drum set, keyboard, or other musical instrument. These are not really examples of acoustic modeling, but rather the use of virtual instruments -- what we used to call samplers -- dominates much of the commercial music released these days. Classic tube microphones have undergone the same modeling treatment.

Measuring and Modeling

Smyth_Realiser_A16.jpgTechniques exist to carefully measure the acoustic energy that enters our ears using very small and highly accurate microphones placed just inside the outer ear. As I mentioned in my piece on 3D, immersive audio, AIX Studios has been used many times as an ideal listening room and became a favorite of owners of the Smyth Research A8 "room realiser" for measurements. This device recreates the acoustic properties of a listening environment and a specific set of speakers via a processing box and set of Stax electrostatic headphones (or any good quality headphones). Owners of the Smyth box would book a couple of hours in my mixing and mastering room to have their personal Head-related transfer functions (HRTF) measured and loaded into their Smyth devices. When combined with the active head tracker, there is virtually no way to tell the difference between sound produced by loudspeakers in the actual listening space and the digitally created version produced by the Smyth Research A8 and delivered via headphones. In other words, the individuals that were measured in my mastering studio walked away with a $250,000 studio on an SD card.

Many major post-production facilities have their Quality Control people measured in their big dub stages and then sit in a small, closet sized rooms to listen to foreign languages dubs through Smyth boxes. The sound of the big multichannel room is recreated through headphones. Why waste time in the big room when you can model it via headphones?

Drop Down Menu Choices for Cables, Vintage Gear, and Other Tweaks

Here is my million-dollar idea: Let's encourage the use of acoustic modeling to bring the sonic qualities of monumentally high-end, wide-bandwidth, reference audio systems to those of us on limited budgets through the magic of acoustic modeling. If the sound at our ears can be meticulously captured and analyzed, the precise parameters of any sonic factor can be identified and tabulated. The amplitude of all music components, frequency distribution and range, phase relationships, cancellation, distortion, and other elements can be precisely determined and recreated using acoustic modeling techniques. Because so much music is distributed using digital networks and reproduced using software players, it should not be difficult to add some additional code to replicate any sound we want. Let's start with something simple like the "sound" of cables.

We all know the issue of cables being active contributors to the sound of your system is a hotly debated topic. Just over the past couple of days, a commenter called me a troll for not believing in "microdynamic precision" as an attribute of cables. And a review on an Australian audiophile site spent the first few paragraphs dismissing anyone who believes in science and engineering before extoling the virtues of expensive cables. Plenty of audiophiles tend towards the subjective side of this argument instead of accepting the science. But acoustic modeling might be the solution to this vexing issue.

asqp_macdevices_600px.jpgI know Jonathan Reichbach, the principal and owner at Sonic Studio and programmer of the award-winning Amarra software player. What if I could convince him and other makers to add a drop-down menu or a series of check boxes to their players? Selecting a particular setting would add some lines of DSP code to the signal path and model the exact "sonic" characteristics of expensive RCA interconnects, speaker cables, power cords, or whatever. I can imagine buttons and an associated control slider that would allow individual users to add or reduce the amount of "microdynamic precision," "stage presence," "coherence," or "low level detail" to the sound of their systems. Imagine the savings! Instead of having to audition expensive interconnects, speaker cables, and power cords, all of the possibilities would be available as plug-ins in the digital music players. If there are in fact measurable differences in the acoustic waveforms that reach your ears when a $1000 USB or HDMI cable is swapped in over a standard issue cable, then we simply measure those differences and program them into the plug-in. I don't imagine high-end cable manufacturers will endorse this effort, but the march of technology is unstoppable.

One of my favorite cable attribute check boxes would provide the ability to change the direction of the cable for those that believe electrons flow better in one direction in a cable. If you can measure it, then we can model it.

But the sonic "benefits" of cables would be just the start. Debates will certainly continue over whether there are actual measurable differences between cables of various types. It might be interesting to review the raw data from the capture stage of our analysis and see whether different power cords produce different waveforms at our ears.

However, there is no doubt that electronics are capable of producing different sonic signatures. The innovative company that backs this idea could acquire the "best of the best" audio equipment, analyze the circuitry, build software equivalents, and provide presets that would replicate the characteristics of equipment made by well-known manufacturers like McIntosh, Meridian, Goldmund, and others. Users would be able to pick their favorites by simply scrolling through a list on a touch screen and hitting the Select button.

Speakers from audiophile manufacturers like Wilson, Magico, and B&W could also be acoustically modeled and replicated just like electronics. In fact, modeling speakers could potentially have the greatest benefit. Audiophiles could purchase a very capable set of full range speakers and have them digitally "tuned" to match the characteristics of speakers costing 100 times more.

The Possibilities are Endless

It would be possible to take things a step further and replicate processes like Master Quality Authenticated (MQA) or Fidelizer through acoustic modeling. After all, the inventors of MQA used similar analytical techniques to measure the "sound" of the original masters in order to preserve that sound when properly reproduced using their licensed -- and very expensive -- decoders and software tools. What if someone simply measured the signals reaching our ears through an expensive MQA equipped system and altered the final output signal to match the MQA version through acoustic modelling? There's no reason why this couldn't be done. Really.


Audiophiles deserve accurate information about all of the components that contribute to reproducing the absolute sound. From hardware to software, power cords to digital interconnects, we need to maximize fidelity without maximizing costs. Acoustic modeling is the answer. Or at least it's an answer. The work and impact that Marcus Ryle and Line 6 have had on the musical instrument industry was revolutionary. The plug-ins that Waves and Izotope provide to the recording industry have been transformational. Who needs rare and expensive tube equipment anymore when an equivalent is available in a drop-down menu on Pro Tools? It's time for the audiophile industry/consumer electronics industry to embrace acoustic modeling too. No more $600 RCA cables! No more $8000 Ethernet cables! Anything that can be done in the analog domain can be done in code. Welcome to the analog future through digital modeling!

Additional Resources
Will Apple's AirPods Pro Start a 3D Audio Revolution? at
AV Bliss Is About More Than Merely Audio and Video at
Is Sony Giving Atmos Fans the Shaft with PlayStation 5? at

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