Upsampling, Reclocking and Digital Filters

The CPLD MAX II (Complex Programmable Logic Device) Altera is used for re-clocking, which together with the XMOS microcontroller brings high-quality processing of both PCM, DSD and MQA technology. Upsampling and reclocking can be individually turned on and off for PCM signals. DSD and MQA use their own format specific settings and filters. For PCM signals, the Nu-Vista DAC has eight selectable digital filters. One of them is our proprietary optimal transient digital filter. In this filter we trade off frequency domain performance for optimum time domain performance resulting in a slight frequency roll-off at 20kHz, but zero pre-ringing and zero post ringing.

Oversampling Bypass

For ultra-high-res audio we have gone the extra step and created our oversampling bypass mode. For sample rates of 705,6k and 768kHz the DAC’s oversampling FIR filters are bypassed and the Nu-Vista DAC goes into oversampling bypass mode. At these ultra-high sample rates, the digital signal enters the DAC block directly. Effectively, this turns off all remaining filtering, improving audio parameters and the frequency spectrum by yet another step. The oversampling filter is the largest single digital section “block” on the ESS DAC chip by silicon area. By powering this filter block down, we reduce the on-chip PSU / ground noise and consequently lower signal correlated clock modulation on the ESS DAC’s silicon die.

The Nu-Vista DAC merges digital with the analogue Nuvistors. Digital to analogue converters, compared to analogue tube devices, present their own design challenges. They work in different domains, have their own requirements and need to be treated as such. We have always held circuit board design and layout up to the highest of standards at Musical Fidelity. We are not believers of flashy board design just for the sake of looks. The design & layout need to be custom-tailored to each application, measure well AND sound as envisioned. Only then have we done our job. At this point, we have given the listener a palpable sense of the recording venue that places the performers in a real-time holographic space in their own homes. We hope you derive as much pleasure listening to it, as we had creating it.