Empirical Audio Off-Ramp 4 USB format converter Page 2
Up to this point I'd been using a generic USB cable with the Off-Ramp. I now substituted the expensive AudioQuest Coffee cable ($295/1.5m). If I heard a difference, it was very small, but if I had to swear on J. Gordon Holt's unwritten autobiography, I'd say that the AQ continued in the same direction the improvement I'd heard with the battery supply.
I spent the rest of that day trying to measure the differences between these two USB cables. It proved as frustrating as a snipe hunt, though I did find a very slight difference in jitter between the AudioQuest and generic cables with the Transporter: The generic USB cable was better.
I then got back from Erick Lichte the dCS Debussy, which Erick had been using as a reference for a forthcoming review of another state-of-the-art DAC, and which Michael Fremer raved about last January. The Debussy, of course, has its own asynchronous USB input, but for a week or so I repeated the comparisons between the Halide Bridge attached to the Debussy's BNC S/PDIF input and the Off-Ramp 4 attached to its AES/EBU input.
Well, as definite as had been the differences between the Halide and Off-Ramp with the Transporter, and between the wall-wart and battery-powered Off-Ramp, the sound was consistently excellent with the Debussy. While the Off-Ramp perhaps still had a slight advantage in soundstage size and focus, it was not a difference I could confidently detect with every recording. Similarly, the small sonic differences I thought I had identified between the generic and AudioQuest USB cables with the Transporter were nonexistent with the Debussy.
The next test was to drive the dCS's own USB input from the Mac mini. The harpsichord continuo in the St. Matthew Passion now occupied more of its own space compared with the Off-Ramp and AES/EBU connection. However, while the soundstage was equally detailed and stable, voices within the soundstage sounded a little more robust and slightly more forward. In the context of my system using the TAD Compact Reference monitor speakers, I preferred the sound with the Off-Ramp 4. When I switched to the more mellow-balanced Sonus Faber Amati Futura speakers, the Debussy's USB input proved a better match.
Re-reading this section, I see that it appears that I listened exclusively to baroque music to derive my impressions. While I believe that component choice does affect one's choice of musicperhaps subconsciously, one selects recordings that play to a system's strengthsI found my listening impressions consistent over a wide range of recorded musics. The enlarging of the soundstage and improved focus of audio objects I found with the Bach recordings was just as evident with the "Dark Star"/"Saint Stephen"/"The Eleven" progression on the Grateful Dead's Live/Dead (ALAC files ripped from CD, Warner Bros. 1830-2).
I have said nothing about the Off-Ramp 4's I2S output. This is because I don't have a DAC fitted with the appropriate input. However, on Steve Nugent's advice, I inserted a loading plug in the Off-Ramp's I2S output so that it was correctly terminated.
Nor have I said anything about the sound of the Off-Ramp 4 with 4Fs audio data; ie, data sampled at 176.4 and 192kHz. This is because, during almost the entire review period, the only DACs available to me that would accept high-speed data were the Transporter, which is limited to 96kHz, and the Debussy, which can accept 4Fs data only via a dual-AES/EBU connection. But just as I was about to turn in the text for copyediting, John Marks sent me the review sample of the Bricasti M1 DAC, which he had enthusiastically written about last August, and which accepts sample rates up to 192kHz via its AES/EBU input. As I write, I can confirm that the Off-Ramp 4 does work well at 192kHz. Readily apparent was the unexpected benefit of the very high sample rate that I have experienced before: the low frequencies firmed up and became better defined. Ray Brown's double bass in "Exactly Like You," from Soular Energy (24/192 ALAC file ripped from DVD-Audio, HiRez Music HRM2011) is a very well-recorded instrument at 96kHz; at 192kHz via Pure Music, the Off-Ramp 4, and the Bricasti, it had more in common with the real thing.
In the New Year, I will report in a Follow-Up more about the Empirical Off-Ramp 4, the Bricasti M1 DAC, and the 192kHz USB upgrade to the dCS Debussy, and compare all three to Ayre Acoustics' DX5 universal player.
Even without its matching Monolith battery supply, Empirical Audio's Off-Ramp 4 is the most expensive of the USB converters I have reviewed in the past couple of years, which range from the Musical Fidelity V-Link ($149) to the Lindemann USB-DDC 24/96 ($650 at the time of the review). But in the right system, the Off-Ramp 4 will give the best sound quality I have heard from an outboard USB converter, and will operate successfully at up to 192kHz sample rates. The paradox is that its benefit becomes less audible the better the D/A processor is at rejecting jitter. The question whether purchasing the Off-Ramp 4 is a cost-effective strategy to getting better sound, compared with upgrading the DAC or buying the excellent but less-expensive Halide Bridge or the very good and very cheap V-Link, will depend very much on the owner's current DAC. But there is no doubt that the Off-Ramp 4 is a well-engineered product that can give superb sound quality from your PC.