Authors: Jim Kotsakidis, Iliyan Selenski
Introduction
If you’ve already optimized your streaming setup with high-quality Ethernet switches, clean power supplies, and galvanic isolation, you’re well ahead of most audiophiles. But for those chasing reference-grade performance, there’s still more ground to cover — and it starts where the streamer meets the DAC. In this final part of the series, we look at advanced optimisation techniques using asynchronous USB, digital-to-digital converters (DDCs), I²S output, and 10MHz master clocks. These tools let you take control of signal timing, clocking, and digital purity — the final frontier before analog conversion.
Part 3: Advanced Digital Optimisation – USB, DDC and Master Clocks Explained
Dive into the heart of your signal chain and learn how to unlock the full sonic potential of your DAC and streamer.
USB Audio: Not All USB Outputs are equal
USB has become the dominant digital output on modern streamers, but its reputation in audio is mixed — and for good reason.
Why USB Audio Can Sound “Off” in Some Systems
- Shared data and power lines: Noisy 5V power rail can leak into sensitive DAC circuitry
- Electrical noise from USB host: Ground plane and switching interference
- Inconsistent clocking: Some DACs still rely on host timing or suffer from jitter at the USB receiver
The result? High-res tracks with plenty of resolution on paper, but a clinical or flat presentation that lacks depth and warmth.
Enter the DDC: USB in, I2S Out, Sonic Transformation
A Digital-to-Digital Converter (DDC) takes USB input and outputs a clean, synchronous digital stream via I²S, AES/EBU, or SPDIF. A DDC acts as both a signal cleanser and format translator. It discards the noisy USB source clock and re-clocks the digital stream using its own high-precision clock. With outputs such as AES, coaxial, and I²S, it gives your DAC a significantly cleaner, lower-jitter input — often resulting in better bass articulation, greater tonal separation, and improved timing cohesion. DDCs are especially useful if your DAC’s internal USB receiver is less refined.
What a DDC Does:
- Reclocks, the incoming signal with a high-precision femtosecond or atomic-grade oscillator
- Isolates, noisy USB host (like your streamer) from your DAC
- Converts, USB to I²S (or other formats) for DACs with compatible inputs
Audible Benefits of Using a DDC:
- Tighter imaging and soundstage
- Smoother highs and improved treble tone
- More natural transients and decay
- “Blacker” background due to reduced jitter and noise
Well-regarded examples include the Denafrips Iris, Denafrips Hermes and Denafrips Gaia.
I2S: The Cleanest Digital Signal Path?
If your DAC supports I²S over HDMI or RJ45, this can be the most direct and jitter-resistant format. I²S sends digital audio as separate data and clock lines, avoiding the timing-recovery issues of SPDIF or AES. This directness eliminates a layer of complexity, ensuring the DAC receives a low-jitter, phase-locked signal. Denafrips supports I²S over HDMI with a defined pinout, and using it often results in a more natural and three-dimensional soundstage — particularly with high-resolution content. However, since I²S is not standardised across brands, matching pinouts is essential. — I²S Recap:
- Separates clock and data signals (unlike SPDIF)
- Doesn’t require embedded clock recovery
- Matches the internal data bus used inside most DAC chips
Note: I²S is not standardized across manufacturers. Always match pinouts between DDC and DAC.
The Master Clock Question: Should you add a 10MHZ Clock?
Some DACs, DDCs, and switches (like the LHY SW-6) offer 10MHz clock input to synchronize their timing to an external master clock.
Why Use a Master Clock?
- Minimizes phase noise across multiple digital components
- Ensures timing consistency between DDC, DAC, and Ethernet switch
- Can yield subtle but audible improvements in:
- Harmonic decay
- Imaging coherence
- Overall timing precision
When It’s Worthwhile:
- You’re using multiple clock-capable devices (e.g., DAC + DDC + switch)
- Your DAC is highly revealing and transparent
- You’re aiming for reference-grade playback
Examples: LHY OCK-2 master clocks
Putting it all together: The optimised path
Here’s how a fully optimized digital front end might look:
Router │ [FMC + LPS]── Fiber ──[FMC + LPS] │ [LHY SW-6 + OCK-2 Clock] │ [Streamer → USB → Denafrips Hermes DDC] │ I²S (HDMI) to Denafrips DAC
Optional: Add a 10MHz master clock to sync switch, DDC, and DAC for final timing refinement.
Recommended Upgrade Path (Priority Order)
| Priority | Upgrade | Why It Matters |
| 1 | Add a DDC (e.g., Denafrips Hermes) | Provides galvanic isolation, reclocking, and format flexibility. It’s often the single most transformative upgrade in digital audio |
| 2 | Use USB → I²S instead of AES | USB + I²S allows asynchronous control and separate clock/data lines, outperforming AES in timing accuracy when well-implemented. |
| 3 | Ensure your USB source is isolated | Using a quality streamer or PC with low-noise USB output (or USB conditioning) improves results, especially before the DDC stage. |
| 4 | Add a 10MHz external clock | Synchronises DAC and DDC timing, reducing phase jitter. Provides subtle but important refinements in top-end systems. |
| 5 | Use high-quality I²S and USB cables | Minimises signal degradation, helps maintain timing, and ensures consistent signal integrity. |
Tip: Always upgrade in a way that supports your DAC’s capabilities — there’s no benefit in reclocking or I²S output if your DAC doesn’t support these inputs well.
Final Thoughts: Listen, Then Trust your system
You don’t need to add everything at once. The key is to:
- Start with clean power and signal isolation
- Use a good DDC + I²S if your DAC supports it
- Explore external clocks only when the rest of the chain is resolved
Remember: even the best clocks can’t fix a noisy source, and not every change will suit every system.
Trust your ears — and listen for:
- Depth
- Transient clarity
- Tonal density
- Overall musical ease
Every point in the chain either removes noise, improves timing, or preserves digital integrity. The result is greater musicality, resolution, and ease.
References
- Denafrips. (n.d.). Hermes, Gaia and Iris Product Specifications.https://www.vinshineaudio.com
- Audio Precision. Measuring Jitter in Digital Audio Systems. https://www.ap.com/technical-library/measuring-jitter-in-digital-audio-systems/
- Julian Dunn / Prism Sound. Jitter: Specification and Assessment in Digital Audio Equipment. https://www.prismsound.com/downloads/misc/jitter_specs.pdf
- Hans Beekhuyzen. Jitter in Audio Explained. YouTube.https://www.youtube.com/watch?v=zTn2L_uKq-I
- Texas Instruments. Understanding and Reducing Phase Noise and Jitter. https://www.ti.com/lit/an/snaa038b/snaa038b.pdf
- Xilinx. Jitter Basics – Understanding Timing Variations in Clock Systems. https://www.xilinx.com/support/documentation/white_papers/wp350.pdf
- PS Audio. What Is Jitter? https://www.psaudio.com/blogs/pauls-posts/what-is-jitter