The front of a hi-fi playback chain, as it has been reviewed here: digital-to-digital converters, the digital transport between a computer and a DAC. They take the computer's USB stream, reclock it against their own oscillator and hand the DAC a cleaner interface - I²S, AES/EBU, coax or optical. Each review says what that change did to the DAC it fed, and what it cost.
Filter the digital source reviews below by list price and connectivity.
2 digital source reviews.
Highest-scored digital source review so far: Denafrips Hermes 12th Anniversary, 8.9/10, Highly Recommended. Rank the list by score
U2 Pro6.5
A $70 XMOS XU316 DDC reclocker (USB-C in; TOSLINK, coax, I²S out). Tighter timing and a fuller, more detailed sound - at the cost of some air and openness.
Hermes 12th Anniversary8.9
A serious DDC with OCXO clocking, FIFO reclocking, dual I²S outputs, and two BNC clock inputs - removes the veil between your source and DAC without coloring the sound.
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The buying guides that rank these reviews, and the free calculators that answer the questions they raise.
A DDC converts nothing to analog, so it can only be heard through a DAC, and each one here was heard on the catalogue's reference chain with the DAC, its volume setting, the amplification and the recordings held constant. That constraint matters more here than anywhere else in a system: the differences a clock and a buffer make are smaller than the differences at the loudspeaker end, and anything else changing at the same time would swamp them. The listening was sighted, so a difference these reviews describe is the writer's impression; none was checked blind.
Judged against Denafrips Enyo 15th DAC Denafrips Hades 12th Preamp
Standards these reviews refer to AES17 Measurement terms ITU-R BS.1116-3 Blind testing
A score here compares best with the other scores on this page. What earns the points on each of the five rubric axes (how a score is built) is specific to the category, and in digital sources it is this.
What actually reaches the DAC scored under Technical performance 25%
Whether the stream arrives unmodified - no silent resampling, no DSP by default - and what the unit's own clock does to its timing on the way through. Bit-identical and well-timed are two different claims, and both get checked rather than assumed from the spec sheet.
What it changes, and what it costs scored under Sound 30%
A reclocker is heard as a change in the DAC it feeds: a darker background, a firmer center image, more detail - or, just as often, a trade, where the same electronics that add body take air and stage width away. The review says which, and a unit that adds a color of its own is described that way rather than scored as neutral.
Behavior at the edges scored under Technical performance 25%
A spec sheet describes the comfortable case. What gets tested is the claimed limit: the top of the converter's sample-rate range, DSD passthrough, the UAC mode a console needs, the I²S pinout a particular DAC expects.
Connectivity and integration scored under System fit 15%
The inputs and outputs for the role - USB, AES/EBU, coax, optical, I²S over HDMI or RJ45, external clock inputs - and whether the unit slots into the system that already exists. A DDC is only as useful as the DAC input it can reach, so the one a reader's DAC actually has is the one that matters.
Build, power and value scored under Build & comfort 15% + Value 15%
Chassis, connector quality and, above all, the power supply: a clock is only as quiet as what feeds it, so a linear supply and its isolation from the digital stage are part of the product, not a footnote. Value is the same question it is everywhere else - what the box does against the reference at its own price.
How to read the scores: A 9.0 here would do its one job with no audible cost and no condition on when to use it. An 8.0 to 8.9 is a genuine improvement to the DAC it feeds, with a stated condition - the Denafrips Hermes 12th at 8.9 lifts a veil without coloring anything, but it cannot fix a DAC whose own character is the problem. Below 7.0 means a real trade: the Douk Audio U2 Pro tightens timing and takes air and stage width away doing it, which is a 6.5 rather than a pass because the trade is genuine and some systems will want it.
We do not score a converter by femtosecond figures on a data sheet or by the reputation of the category it sits in. What the unit does to a real stream, heard through a DAC and a chain that do not change between tests, is the thing; everything upstream of that is an input to the verdict, not the verdict.
Buying advice, terminology, and how the digital sources category is reviewed on The Audio Stuff.
A digital-to-digital converter takes the stream from a computer or streamer, buffers it, reclocks it against its own oscillator and hands your DAC the same audio on a different interface - usually I²S, AES/EBU or coax instead of USB. It converts nothing to analog, so it never replaces a DAC; it replaces the DAC's input stage and clock.
Sometimes, and how much depends on the DAC. If its own USB receiver and clock are its weak point, reclocking in front of it can be an audible change; if it already has a good input stage, you are paying to replace something that was not the limitation. It is a component to try against your specific DAC, over days and at matched levels, rather than to buy on principle.
The reviews here cannot settle it, because both were sighted listening. On the review system the Denafrips Hermes 12th lifted a veil between source and DAC and widened the stage without coloring anything, and the Douk Audio U2 Pro tightened timing and filled out the body at the cost of some air. Neither difference was checked blind, and a DDC changes little enough that a blind ABX comparison, with levels matched, is the way to learn whether you hear it without knowing which one is playing. Whether a change is an upgrade also depends on the DAC and the system, which is why the two verdicts differ.
I²S carries the clock on its own line rather than embedding it in the data, so the DAC does not have to recover timing from the stream. It only helps if your DAC has an I²S input, and there is no single wiring standard for I²S over HDMI or RJ45, so the DDC has to offer the pinout your DAC expects.
A transparent one reveals more of what the DAC already is rather than adding a character of its own - so if the DAC's tonality is what you dislike, a DDC gives you more of it, and the fix is a different DAC. A DDC that does change the tone, as the U2 Pro does with a fuller body and less air, is making a trade, and the review says so.
