The Gustard U18 USB digital audio interface offers high quality, high performance and accurate audio reproduction. Its input stage is a second generation XMOS XU216 USB interface with 16 cores and a 200 Mbps decoupler to eliminate interferences. Signal processing and necessary corrections and precise control are handled by an Altera MAX II CPLD. A Gustard K2 noise synthesizer and two Accusilicon AS338 oscillators are used to generate the highly accurate clock signal with a jitter of only 38fs. The clocks are powered cleanly by an LT3045 linear regulator with a noise floor of just 0.8µVrms. The power supply incorporates a high performance toroidal transformer optimised for audio use. Outputs are Toslink optical, coaxial, AES/EBU and I2S HDMI, the latter supporting high-resolution audio streams up to PCM 768 kHz and DSD512 resolution. I2S output is configurable for devices using different pin-outs.