AUDIOTRAK GlassBlack2plus / ATC-GB24 Optical Digital Cable Impressions｜Part 2

AUDIOTRAK GlassBlack2plus – ATC-GB24 Optical Digital Cable: Construction

Now, the guest of honour for today’s test: the optical digital cable I have newly added to the “AUDIO STYLE” system — the AUDIOTRAK GLASS Black ATC-GB24. The biggest difference from the inexpensive TOSLINK cables mentioned earlier is that, while this cable uses glass fibre rather than plastic fibre (acrylic fibre) for its core, it has been kept within a price range that budget Hi-Fi enthusiasts can actually reach.

The core consists of 280 strands of ultra-fine glass fibre, each 53 microns in diameter — and picking it up, I was surprised at how soft it feels, on a par with plastic-core optical cables. Being soft, however, does not mean it can be handled carelessly — forcing it into sharp bends risks creating numerous small fractures inside the cable, which left me feeling rather worried just holding it. The manufacturer does state a minimum bend radius of 65.0 mm (diameter). Given how limply it droops under its own weight, maintaining a bend radius of R65 mm or more in actual use is going to be tricky… Anyway, I carefully connected it to the PIONEER SuguReco DVR-DT100, making sure to avoid any bends of less than 6–7 cm at the back of the unit or around rack edges…

Glass Black ATC-GB24: Sound Quality Review

The first difference I noticed compared with the audio-technica AT-OPX1 I wrote about earlier is in how the soundstage spreads. Whereas the AT-OPX1 opens up a wide soundstage that extends upward and rearward, the ATC-GB24 presents its sound in the space between the two speakers. Its imaging sits lower than most optical digital cables. Put another way, the soundstage may feel slightly narrower than the AT-OPX1. In particular, there is none of the floaty, exaggerated high-frequency extension that TOSLINK cables tend to have — dialogue and vocals are placed properly lower, snapping neatly into place at the centre point between the two tweeters.

And within a soundstage that is not especially wide — yet not narrow either — there is a sense of particulate information density, like diamond dust, that I have not encountered with other optical digital cables. Another characteristic is the fast transient attack, with a sharp, high-speed leading edge. That said, you might expect the high frequencies to stand out prominently, but they do not — the overall character is accurate, monitor-like, and earnestly neutral. On top of that, the peculiar lukewarm sense of echo and colouration that TOSLINK cables tend to add (a delay inherent to optical cables, perhaps?) is notably reduced. It gives the impression of having stripped away the excessive tinting that digital cables often add.

The transient attack is fast, but with AAC-compressed television content played via the PIONEER DVR-DT100, there are moments where the midrange definition and openness of dialogue and vocals feels somewhat lacking — a slightly nasal, congested quality. (Note added later: after continuing to use it for several months, this problem mysteriously resolved itself.) This is probably because… the quality of the compressed audio output from SKY PerfecTV! and the DVD recorder itself is not great, and unlike the audio-technica AT-OPX1 — which pleasantly softens such things — the GlassBlack delivers the jitter and noise as information, as-is. Also, for an optical digital cable, the low-frequency extension is reasonably good and resolution is high — though that is with the caveat that we are still talking about a TOSLINK cable. When the low-end of the GlassBlack ATC-GB24 is compared against a coaxial digital cable with a well-regarded bass response and weight, it does come across as somewhat lean.

To be honest, at this point I was beginning to wonder whether buying it had been a mistake. My main reason for bringing the AUDIOTRAK GlassBlack ATC-GB24 into the system was to connect AV equipment lacking a coaxial digital output to a standalone D/A converter. But with the PIONEER DVR-DT100 specifically, while the added information retrieval was welcome, the vocal openness — the thing that matters most — was not quite right. The presentation was earnest to a fault, lacking in charm and not particularly engaging. Going back to the audio-technica AT-OPX1, the soundstage opened up, a modest sense of life returned, and television became fun to listen to again — yet in terms of objective sound quality, it was nowhere near the AUDIOTRAK Glass Black ATC-GB24… and that left me in a bit of a dilemma.

But then, better sound quality means nothing if you can’t enjoy the music — and that is simply true. For the time being, I switched the SuguReco’s optical digital connection back from the GlassBlack ATC-GB24 to the audio-technica AT-OPX1, and this time tried connecting the GlassBlack between the main system’s CD player, the CEC TL5100Z, and the same standalone D/A converter as before, the Firestone Spitfire 24bit DAC (page under construction). In this combination, with the inexpensive optical digital cables mentioned earlier, none of them — whichever I tried — could hold a candle even to the yellow composite video cable (75Ω coaxial video cable) that used to come bundled with old video equipment. I was half resigned to this being the limit of optical digital output — TOSLINK’s ceiling, so to speak — but when I connected the GlassBlack ATC-GB24, well, to my considerable surprise, it quite straightforwardly sounded far better than the yellow cable.

The GlassBlack’s character is cool-toned, with a chilly temperature, a hard, disciplined, earnestly matter-of-fact musical presentation, a high-speed leading edge and crisp definition that handles instrumental separation reasonably well, and a good sense of S/N. The subtle powdery quality in the mid-to-high frequencies that had been nagging me with the Firestone Spitfire 24bit DAC (page under construction) — possibly inherent to higher-order oversampling — receded, replaced by the GlassBlack’s own character: a cold, clean, dry frizzante-like sensation going down (don’t ask). It is not what I would call an optical digital cable with exceptional “musicality” in the way I usually mean that phrase, but it is straightforwardly good-sounding. Monitor-like, crisp, and precise. Piano in particular has a pleasing transparency and clarity of outline — rather a captivating tone.

The CEC TL5100Z, like other CEC belt-drive transport models bearing the hand of Carlos Candeias, has a warm, smooth, analogue-tinged sound with body in the mid-to-low frequencies. The Firestone Spitfire 24bit DAC (page under construction) connected to it is modest and neutral in character. The belt-drive’s sound tends warmly, smoothly, and with a certain looseness — and by routing through the AUDIOTRAK GlassBlack ATC-GB24, an appropriate degree of tautness, firmness, and transient speed is restored, pulling the temperature back toward neutral. Musicality and vitality come from the CD transport side; the glass fibre cable adds a monitor-like sense of high-resolution clarity, injecting it into a DAC section whose virtue is faithful, if somewhat plain, reproduction — each of the different characters married together, and the balance, remarkably, works out beautifully.

～ Summary ～

· A studio-monitor-like, crisp tonal character, grounded in particulate information density and transparency
· If the source equipment is noisy, this cable may actually work against you
· A relatively honest, lean-sounding cable — not the type that actively dramatises or embellishes musicality
· Those coming from the PC audio world tend to appreciate this kind of precise, accurate-feeling sound
· If you are currently using a plastic-core optical digital cable, upgrading to the GlassBlack seems well worth doing
· It does not reach the level of ultra-high-end coaxial digital cables, but there are plenty of coaxial cables in the under-£200–300 range that sound worse than the GlassBlack — so I think it offers more than its price would suggest.

Note added later: the monitor-like earnestness and dry, austere impression I noticed when I first introduced the cable gradually softened as burn-in progressed. The fine, delicate frizzante quality remained, but alongside the density of information, a transparency and a pleasing moisture to the resonance emerged, and at some point it had shifted into a natural, easy way of sounding. I would not normally expect burn-in to apply to an optical digital cable, but with this ultra-fine multi-strand glass fibre construction, I suspect that over the course of repeatedly inserting and removing the plugs, microscopic cracks have formed inside — and that, paradoxically, the sound has become more appealing and supple as a result.

The switching tests between optical digital cables were more taxing than I expected… TOSLINK has a quality — for better or worse — of being somewhat colour-drained compared with coaxial digital: its character is thin. With plastic-core cables in particular, quality tends to stay within a certain ceiling, and it is hard to perceive the kind of immediately identifiable character you get with coaxial digital or analogue RCA cables. With AV use, watching video content every day, it is more the gradual accumulation of small differences — the atmosphere and nuance of dialogue, something quietly nagging away at you over time…

Come to think of it, I seem to have lost the protective caps for the optical digital cable terminals somewhere during all this swapping — the count has been quietly dwindling, and before I knew it they had fallen victim to the vacuum cleaner. I keep wondering if you can buy replacement caps somewhere. Also, the square TOSLINK plug is fiddly to seat correctly at the best of times, and with a round plug you cannot tell by touch which way up it goes — making blind insertion quite stressful. It is a shame that only the audio-technica AT-OPX1 does anything sensible about this. Though I should note that audio-technica’s higher-end models using quartz cores — the AT6D40, AT-EDP1000, AT-SDP2000 (page under construction) and so on — do use round plugs as well…

Finally — the “Netsuken OPTICAL GATE” I used to use as my reference optical digital cable: I have a feeling it sounded even better than the ATC-GB24… though that may simply be a romanticised memory. It suffered a spontaneous cable break, and I rather wish it would come back to life somehow… (sigh)

It had stopped transmitting light, so on a whim I cut it in half — and one side did light up again. However, even with the glowing end inserted into the optical terminal, the DAC unfortunately refused to recognise it. Glowing alone is apparently not enough… I wonder whether there is some kind of optical lens element required at the plug end? (If it ever miraculously comes back to life, I would like to write up a comparison review.)