Product Reviews

Reprinted from November 1999
Vol. 22 No. 11

TDS Passive Harmonic Enhancement System

Audiophiles are, for the most part, "purists": no equalizers in the circuit (never mind that the RIAA section of your phono preamp is one), no effects boxes or extraneous electronic clutter. You older guys and gals maybe flirted with a Dynaco Quadapter and a pair of surround speakers in the '70s (I did), or maybe even a Barcus-Berry BBE processor in the '80s (tried it, didn't like it - it added things to the signal that were not originally there). But usually, after adding something that delights us for a while, we end up ripping it out and going back to the simplest setup possible.

Had TDS's ( little $395 black box not been lurking in the KR Enterprise/Von Schweikert system that stopped me in my tracks at last year's CES, I probably wouldn't have bothered with it. But TDS's VP of marketing, Chris Knecht, and Art Garcia, who co-invented the patented process, offered it to me for review, and I agreed.

The Passive Harmonic Enhancement System (PHES) is a totally passive, signal-source driven inductive circuit that goes between preamp and amp, or can be used in a tape loop on integrated amps or receivers. There are no caps or resistors, and no power supply. What's in the PHES is a "system of transformer couplings placed in parallel with the source and load of corresponding sound-reproducing equipment," according to TDS, which claims a bandwidth of DC-l00kHz. TDS also claims low harmonic distortion for the process, and says it introduces no phase changes, time delays, or harmonics.

Nor does it have to be in a black box. Art Garcia demonstrated a software solution that applied the PHES process to the tiny speakers built into his laptop. It can also be put into an analog or digital IC, or even built into a set of interconnects. According to Garcia, the PHES process nonuniformly amplifies "select frequencies already present in the audio signal that are not as perceptible to the human ear." We all know the Fletcher-Munson equal-loudness-contour curve, right? According to TDS's literature, the sensitivity problem is compounded by the "energy loss that an audio signal experiences during the playback process." Garcia got into this via his father, who was researching and developing a sound process that would enhance Sonar recognition. The younger Garcia, an audiophile, along with his father, decided to find a way to incorporate the technology into audio.

The transformer coupling results in a 3dB voltage gain, so all comparisons were done using an SPL meter to ensure levels were equalized. "First, do no harm," is the primary demand I place on any "enhancement" technology, so that's what I listened for first, using delicate, detailed source material like Classic Records' The Royal Ballet 45rpm reissue. I also used DCC Compact Classic's superb reissue of Nat King Cole's "Love is the Thing," and both an original Vanguard pressing and Analogue Productions' reissue of Songs of the Auvergne which features an ultra-natural recording of a female voice. I also listened to a 45rpm British 12" of Pete Townshend and Ronnie Lane's string-drenched and brilliantly recorded "Street in the City," from Rough Mix. I auditioned the TDS box in my old listening room and my new one, through Audio Physic Virgos and Sonus Faber Amati Homages.

On the negative side, there was a barely perceptible loss of transparency and high-frequency sparkle, and a slight muting of the leading edges of transients. On The Royal Ballet, for instance, there is a delicate tambourine placed at the back of the stage. With the PHES, a slight opacity set in, reducing the shimmer. The pick-on-guitar-string sound in "Street in the City" was slightly dulled. But that was it for the negatives, which were very subtle, and not really noticeable except via direct comparison. Still, for some of you that might be enough to just say no.

Fortunately, the positives were subtle yet compelling on most program material. I heard nothing jarring, nothing that let me know I was hearing a "processed" signal. There was no noise, no "pumping," and no sonic seams. Were you to play your system for a friend familiar with its sound, he might not even notice a difference

With the box in, the sound was uniformly richer, yet with greater detail. Instruments seemed to sound more like what they sound like, with better separation. For instance, on "When I Fall In Love," on the Nat King Cole album, the tonal distinctions between violins and cellos were more pronounced than I was used to - and overall, more physically palpable and three-dimensional. The overall soundstage was likewise improved, but just subtly, and proportionally. The effect was pleasing, but neither vulgar nor artificial-sounding.

I liked what the TDS box did in my system. I'll use it, especially when listening to CDs, but I can't agree with some of the wilder endorsements. Recording engineer Tom Dowd (the Allman Brothers, and hundreds of classic Atlantic studio recordings) is quoted as saying "TDS adds back what I would originally hear in the studio, but could never capture on the finished product." Hmm. Eight-time Academy Award-nominated film mixer Rick Kline said that "The music with TDS sounded as if the instruments were placed not only left to right, but spatially throughout the room in a three-dimensional manner, without any apparent sweet spot, as if the instruments were being played before me ... live!" Of course, that's a good description of a properly set-up high-end audio system without TDS.

TDS was used for certain sound elements in Jerry McGuire and My Best Friend's Wedding, which is a Dolby Digital demo disc among videophiles; and the entire final mix of The Mummy was passed through five channels of TDS processing on its way to film and DVD. Even electric-car advocate and "actor/audiophile" Ed Begley, Jr. chimes in: "While listening to TDS on my home stereo system, I knew without a doubt that I was listening to music played before me live! It was truly amazing! There is nothing on the market like TDS. It's easy to install; it's affordable; and most important ... TDS will bring you so much listening enjoyment."

The more modest your system, the more I think the TDS Passive Harmonic Enhancement System will improve it. In any case, this $395 box is available with a 30-day money-back guarantee, so if I've whetted your curiosity you can check it out for yourself risk-free. There's a version for the same price with a switch so you can do your A/B comparisons immediately and conveniently, but that just puts another impediment in the line; go for the switchless model.

Manufacturers' Comments

TDS Harmonic Enhancement Technology


To Michael Fremer... thank you for your time and, more important, your open-mindedness. We, too, enjoy thinking of ourselves as a blow to the purists' theory that "less is more"! Thanks also to Von Schweikert and KR Enterprise for using our systems at CES, and especially to Clement Perry of, who introduced our Technology to those two and to many other manufacturers. Without hearing the attributes of TDS there, as Michael suggested, he might not have had the time or inclination to later review it!

As Michael mentioned, it's important to note that the TDS Harmonic Enhancement Technology is not limited to the after-market Passive Black Box that he reviewed. The same results are also available in distinct TDS audio solutions, including smaller passive-inductive microcircuits, discrete circuit boards designed for IC production, and digital software formats, all of which enhance both broadband (music, movies, etc.) and narrowband (voice for telephone, FRS, CB, police and marine radio, etc.) applications suggesting that it's not just another black box, but rather a pioneer technology.

Finally, as far as Michael not being able to agree with some of the "wilder endorsements" of our TDS Technology. . . we didn't expect him to. Those opinions were stated by audio professionals (sound engineers, mixers, artists, and the like), who are typically prone to describing their music, and their thoughts on it, in such ways. Michael, on the other hand, is a respected audio analyst for the most widely recognized audiophile publication in the world, and therefore we wouldn't expect him to describe his thoughts or opinions that way. Needless to say, Michael notes, "I liked what the TDS box did in my system. I'll use it..." From Michael Fremer of Stereophile, that's good enough for us!

Thanks again.

True Dimensional Sound

TDS Equals "High Fidelity":

Earlier this year, our company received the results (located on our website of comprehensive independent testing performed on our TDS Harmonic Enhancement Technology, utilizing TEF20 (Time, Energy, Frequency) analysis. TEF20 is the industry's most sophisticated measurement equipment and is considered the most accurate and state-of-the-art technology available when analyzing acoustical phenomena. The results, which include detailed graphs, verify our claims regarding the manner with which the TDS Technology operates as well as its resulting enhancement to an audio signal.

When combined with this review from Stereophile magazine, recognized as the world's leader in assessing high-quality audio, the information provides both subjective and objective data from unimpeachable sources that the TDS Harmonic Enhancement Technology provides true "high fidelity" enhancement to any audio signal for both consumer and commercial markets alike. There is no other Enhancement Technology in the world that can pass these tests and stake this claim. TDS is...

The Sound of Tomorrow... Today!TM

True Dimensional Sound, Inc.
1450 Madruga Avenue, Suite 404
Coral Gables, FL 33146
(305) 668-9198

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