After testing every filter permutation, I’ve settled on the slow roll off and Pro-Ject Audio’s Best setting. Why? I favor the combination of overall volume levels and slowly softened highs. This tendency is something new. I used to like the harder, the more detailed, and the faster roll offs. And then I turned thirty five.
In evaluating the S2 Digital, one can’t simply pronounce a sound signature without first running through 8 filter sets, distortion compensation, and a variety of inputs. The S2 requires time.
And the time I’ve given it has been delightful.
Before I discuss the slow roll off setting, let’s instantiate what the S2 Digital nails. I measure THD distortion at 0,0008% in unloaded signals on an ADC system that can measure down to 0,0002%. Stereo crosstalk tops out near -110dB, and both jitter and IMD are ridiculously well controlled- both for the S2’s price and for a bus-powered USB device. By and large, the S2 is load agnostic. Unloaded or no, it keeps its basic frequency response controlled down to a maximum difference of roughly 0,5%. That despite driving an Earsonics SM2, an Audio Technica ES7, or a Beyerdynamic DT880. Of the three, the SM2 stresses it the most, amping absolute THD by 75x at maximum volume (0dB), which may sound extreme, but which ends up at 0,063%, or completely inaudible. It controls IMD at the same volume to 0,1%, which is also inaudible, and represents a jump of 11x from base, unloaded results. Loaded results mimic those of the 3000$ Sony NW-WM1Z, while unloaded THD and IMD and stereo crosstalk scores favour the S2 Digital.
I’m really surprised at how well the S2 Digital drives the ES7 at maximum volume. THD ticks upward from 0,0008% to 0,0009%, and IMD from 0,0089% to 0,020%, and the ES7 is pretty tough to cleanly drive at maximum volume. Speaking of, through my iMac’s USB, the S2 Digital gets about as loud as an iPhone 6, which is enough to drive many headphones, but won’t trounce high-current planars. Through better USB implementations, the S2 can attain higher decibel levels. Coax and optical input results mete out similar results.
Overall, the S2 Digital’s performance is good to great, but not quite top shelf. What is top shelf is its handling of MQA and DSD, not to mention Red Book files. Obviously, both MQA and high sampling rate DSD files require feeding the S2 Digital via USB. Filters work any and all file types. Despite problems in my iMac’s USB implementation, I still prefer listening through it precisely because I can take advantage of everything from MQA to the S2’s remote control.
Let’s talk filters. The slow roll off begins its high-range descent at 5K, dropping by roughly 5dB by 18kHz, viz., it’s a minor roll off certain not to perturb purists. It retains a good amount of high end detail, but rules out the harshest treble spikes. Simultaneously it evens out possible stereo drops under load. All frequencies retain roughly equal stereo sound pressure, which make the S2’s soundstage deep and rich. The total effect smooths out many of the harsh upper-end cues which annoy me about the DT880/600, and which make Susvara sound even richer.
Naturally, the S2 Digital is pushing its limits through both headphones. For my preferences, it nails the DT880, but under extremely dynamic passages in both space and classical music, Susvara needs more voltage. For most popular music, however, the S2 powers that headphone well, just not to loudness extremes. Because it keeps IMD low, even at the loudest volumes you’ll never hear your favourite tunes sheer or clip.
And whichever filter you chose stays active even after powering down. The other filters exact different final opinions, but the S2’s basic tone: rich, tending to midrange warmth, and Z-axis deep stages, change only just.
Before I file out of this section, let’s talk noise: my home has a ground loop. Fixing it is a bugger. Some DACs and amps are more susceptible to it than others. Unattended on the desk, the S2 Digital makes slight shhhhh sounds in the background, but when properly grounded, is dead silent. This goes for hardware hiss as well. It’s as free of hiss as Antelope Audio’s high end Zodiac systems, and on par with some of the best smartphones and DAPs. All of the above satisfy head-fi’s self-declared hiss king.
Because the S2 Digital is rich across the mids and stereo deep, reference-neutral to bright headphones will resolve the greatest accents its of which its filter system is capable. But you can really deep dive with warmer headphones. My favourite combo? Maybe the Grado GH-2, whose stereo depth isn’t in the same league as the DT880 or Susvara. The S2 really focuses on that headphone’s strengths.
The S2 Digital’s filter system should satisfy everyone but the hardcore valve listener. The S2’s got a solid, and largely load agnostic output system. Everything from its remote control to its input array work brilliantly with 99% of upstream sources. It syphons powers via USB and outputs decent power to most headphones. Its rich tones and encompassing stereo output are nearly in a league of their own in the camp of devices that ride on ESS DACs.
It does all this at 349 Euro. In my books, it is a coup.