The levels of jitter are:
1. S/PDIF and AES/EBU: Embedded Clock Jitter
- Typical Jitter Levels:
- Standard S/PDIF implementations can exhibit jitter in the range of 100–500 picoseconds (ps).
- Higher-end receivers and DACs with advanced clock recovery can reduce this to <100 ps, but this depends heavily on the quality of the phase-locked loop (PLL) and signal transmission.
- Worst-Case Scenarios:
- Poor-quality cables, connectors, or noisy environments can push jitter well above 1 nanosecond (ns).
- If the receiver has a poor PLL design, jitter can degrade significantly, leading to audible artifacts in high-fidelity audio.
2. I2S: Separate Clock Jitter
- Typical Jitter Levels:
- With a dedicated clock signal, I2S can achieve jitter in the range of 20–50 ps.
- High-quality clock generators can reduce jitter to single-digit picoseconds (5–10 ps).
- Why Better?
- Since the clock is transmitted separately, there’s no need to recover the clock from the data, eliminating a major source of jitter.
3. USB Audio: Clock and Jitter
- Asynchronous USB Audio:
- The receiving device generates its own clock and does not rely on the USB data rate for timing.
- High-end USB audio implementations can achieve jitter levels below 10 ps with precise crystal oscillators.
- Adaptive USB Audio:
- The clock adjusts dynamically to match the USB data stream, introducing higher jitter (similar to S/PDIF, often 100–500 ps).
Impact of Jitter on Audio
- Jitter Below 20 ps: Practically inaudible, even in high-resolution audio systems.
- Jitter 50–100 ps: Still inaudible for most listeners, but may affect very sensitive audio systems.
- Jitter 200–500 ps:
- Audible for critical listeners, especially in high-frequency content.
- Leads to slight loss of detail, spatial imaging, and clarity.
- Jitter >1 ns: Audible artifacts like distortion, loss of high-frequency precision, and a "smeared" sound.
Summary: Jitter Levels by Signal
| Signal Type | Typical Jitter | Best-Case Jitter | Worst-Case Jitter |
|---|---|---|---|
| S/PDIF & AES/EBU | 100–500 ps | <100 ps (high-end PLL) | >1 ns (poor conditions) |
| I2S | 20–50 ps | 5–10 ps (high-end clock) | ~50 ps (lower-quality clock) |
| USB Audio (Asynchronous) | 10–20 ps | <10 ps | ~50 ps (mid-range setup) |
| USB Audio (Adaptive) | 100–500 ps | ~100 ps | >1 ns (poor systems) |
Conclusion
- S/PDIF and AES/EBU can suffer from jitter up to 1 ns in poor conditions due to clock recovery.
- I2S and asynchronous USB Audio provide much lower jitter, often in the single-digit picoseconds range, making them superior for high-fidelity audio.
This is why modern high-end DACs prefer I2S or asynchronous USB for their precision, while S/PDIF and AES/EBU are more prone to timing errors.
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Tihomir Haralović, M.Sc. in Physics
Zagreb, 15 December 2024