Empirical Audio Overdrive SE USB DAC/PreDAC Review

Empirical Audio Overdrive® SE USB DAC/PreDAC (and Short Block USB Filter)

The Sound

In discussing the sonic characteristics of the Overdrive, I would like to begin with a brief recap of the “evolution” of digital audio. My reason for doing so will, I hope, soon become apparent. The very earliest CD players, and the external DACs that followed, were not very good. The sound was hard, brittle, and edgy, as a result of which the terms “digititis” and “listener fatigue” became part of the audiophile lexicon. In response, some manufacturers, as well as some modders, began adding tubes to the digital players. This approach did in fact make the sound more palatable but was of course little more than a band-aid, as a tube(s) did not, could not, and does not change any inherent flaws that existed in the digital circuitry (nor in any other part of the audio chain, but that is a discussion best left for another day.) What the tubes did do was blunt transients a bit, roll-off the high frequencies a tad, and add some pleasant-sounding lower-order harmonic distortion. This was a reasonable trade-off, as the result was indeed a more enjoyable (or more accurately, a less unpleasant) sound. With time, engineers began to get a handle on the actual causes of “digital sound.”   The first advance was recognizing–and correcting –jitter. While the audible limits of jitter are still a matter of contention, many manufacturers –Steve Nugent amongst them—continue to decrease jitter in their designs. Incredibly, some digital products now have femptosecond clocks. (A femtosecond is 10^-18 second; or in plainer English, one quadrillionth (i.e., one thousandth of one trillionth) of a second!) The next big advance was the recognition that commonly used digital filters produced “pre-ringing.” Pre-ringing is a phenomenon in which an audio transient is preceded by a series of smaller peaks. As is probably apparent, pre-ringing does not appear in nature, and for that reason it is presumed to account for—or at least, contribute to—the “unnatural” quality that some listeners experience with digital audio. Many DACs now include so-called Minimal Phase filters, which dramatically decrease pre-ringing.

With these advances, along with the availability of hi-rez recordings, digital audio no longer needed band-aids. And yet, somewhere along the way, many listeners apparently got used to the softer sound, which is often described as being more “analogue-like.” (This too is a topic of conversation for another day.)   The result is that many modern DACs have a sound that is, at least to my ear, overly soft, and lacking in detail. And this finally brings us full circle, back to the Empirical Audio Overdrive DAC. (As a quick aside, in my limited experience, DACs that convert PCM to DSD do not eliminate this problem and in fact, may even exacerbate it.)

That background sets the stage for describing the Overdrive, which is the antithesis of “overly soft” and lacking in detail. If I were to sum up the Overdrive’s sonic qualities in just a few words, those words would be clean, accurate, precise and fast. By comparison to the Overdrive, most of the other DACs I’ve auditioned sound veiled and slow. Although the Overdrive is not soft, I must emphasize that neither is it hard or harsh. Similarly, though it is not warm, neither is it cold or analytical. The Overdrive is incredibly resolving, and its detail is the result of exceptional clarity; this is in stark contrast with much audio gear which has what should perhaps be called “pseudo-detail,” as it results from a boosting of certain frequencies (in particular, in the upper mids/lower trebles). Gear with pseudo-detail is often described as being “ruthlessly revealing”; though initially ear-catching, this invariably leads to listener fatigue. In contrast, the Overdrive never results in listener fatigue.

A common audiophile term is “musical,” which often seems to be synonymous with warmth. In my opinion, “warmth” is an audiophile construct, which bears little semblance to live music. To my way of thinking, musicality is what results when a piece of gear—or better yet, an entire system—allows all (or as much as possible) of the content of the recording to come through. In this sense, the Overdrive is superbly musical, as it is not only richly detailed, but also close to neutral in terms of frequency response.

I am of the school that believes that dynamics–the change from soft to loud—are a critical aspect of music, and that gear that cannot reproduce appropriate dynamics is flawed and boring. The Overdrive excels at dynamics. This was especially apparent when I used it with the 110 db sensitive, 4-way Sadurni horn system. Need I say more?

In questioning Steve as to how he achieved such incredible clarity and dynamics, he explained that it was due in large part to his use of Hynes regulators, which he feels are in a class of their own. I doubt that is the entire story but however he did it, the results are, in my opinion, unequivocal.

Regarding soundstaging and imaging, the Overdrive presents each musician in its own space, and that space is realistically and appropriately sized. Some other DACs (and other gear in general) I’ve tried have larger images and a generally larger soundstage but in my view, this results from smearing, and is thus an artifact. The Overdrive does not smear; as mentioned above, it is precise, and presents an accurate rendition of what is on the recording, with an absolute minimum of editorializing or coloration.

The Overdrive excels with both Redbook and hi-rez files. It should be noted that it does not do DSD. DSD is gaining a lot of buzz lately, though I believe the jury is out as to whether it is sonically superior to hi-rez PCM. Irrespective, there is currently precious little music available on DSD, and only time will tell whether DSD catches on, or whether it remains a niche format as has its disc-related predecessor, SACD. Whether the lack of DSD capability is a deal-breaker is something each person must decide for himself.

Along with the Overdrive, Steve also included a Short Block USB filter. This small device has a USB input and a USB output, and inserts between the computer and the DAC. It is a passive device, and this does not require power. Steve’s website explains its function as follows:

“The purpose of the Short-Block is to improve audio quality by reducing jitter caused by common-mode noise on the USB cable.

Common-mode noise is voltage that develops on both of the differential signal lines in the USB cable. Ideally, this voltage would never be present or be fully rejected by the receiver USB interface, but in real systems with multiple grounds and imperfect USB drivers and receivers the noise is usually present and impacts audio quality. The Short Block reduces this common-mode noise, primarily at high-frequencies. If you have power-line hum in your system, it will generally not fix this.

The Short Block severs the +5V wire in the USB cable, so devices that rely on the +5V power in the USB cable cannot use the Short Block. The Short Block does not work reliably with the Off-Ramp 3, but works well with recent Overdrives, Off-Ramp 4 and Off-Ramp 5.

Though I was admittedly skeptical there was no harm in trying, so I connected it into the system. Lo and behold, the sound became even sharper, with better focus. At its price of $199 it is an excellent value, providing more improvement than many “tweaks” I’ve tried that cost considerably more.

Most of the visitors to my listening room were wowed by the Overdrive, just as I was.   But of course, the Overdrive will not be for everyone, because tastes vary. This was driven home to me a few weeks ago, when I had a telephone conversation with an acquaintance who is a long-time audiophile. I invited him to come over to hear the Overdrive, explaining that the Overdrive is more dynamic and less colored than his reference DAC (with which I am quite familiar). His response was to tell me that he had no interest in the Overdrive because his current DAC “makes digital sound just like his vinyl.” He thus falls into the category of listener who seeks a particular type of sound, rather than accuracy; in this case, the type of sound he seeks is one that was imprinted over many years of listening to vinyl (with its own attendant artifacts). Such a listener would, I suspect, find the Overdrive to not be warm enough for his taste. However, for the type of listener who wants to hear what is on the recording, the type who places a high priority on dynamics and lack of coloration, the Overdrive is non-pareil. Any such listener who is in the market for a DAC should most assuredly audition the Overdrive. It is outstanding in every way, outperforms many more expensive DACs, and I unequivocally give it my highest recommendation.