Digital
Digital compatibility
Bits match or they don't — and a working digital cable is sonically neutral.
Simple
Checks that your source and DAC speak the same digital language — same file formats, sample rates, and bit depths — and that the cable isn't too long. If they match, the data arrives perfectly and the cable makes no difference to the sound. Full stop.
The theory
A digital link transmits discrete numbers, not a continuous waveform. As long as the receiver locks to the data and recovers every bit, the output is identical regardless of cable — there is no "warmer" or "more detailed" USB cable. The engine verifies format overlap (PCM/DSD), that the DAC's max sample rate and bit depth meet or exceed the source's, and that cable length stays within the connector's reliable limit. Failures here are categorical (no shared format) or bandwidth (high-res gets downsampled), never tonal.
For experts
This is the engine's honest-cable stance made explicit. The one real-world wrinkle is jitter — timing error in the clock recovering the bitstream — which can be cable-influenced on self-clocking interfaces like S/PDIF and AES3, where the clock is embedded in the data. But two things defang it: (1) asynchronous USB and any link where the DAC reclocks from its own buffer make the source clock irrelevant, and (2) measured jitter in competent modern DACs sits 100+ dB down, far below audibility thresholds established in controlled listening. So the model reports bit-perfect links as having no sonic effect, flags only genuine bandwidth/length problems, and refuses to launder jitter anxiety into a cable recommendation. Length limits are physical, not mystical: ~5 m for unrepeated USB 2.0, ~10 m for TOSLINK before the LED's rise-time smears the eye pattern, longer for AES3 over proper 110 Ω cable.
Nyquist: a locked, bit-perfect link preserves everything below half the sample rate — cable brand does not appear in this equation.