The S/PDIF coax audio signal supports 44.1kHz to 384kHz sampling rate at 24-bits for an effective signal rate of about 50Mbps - or 100MHz of bandwidth. Dual-coax (DX) is just two parallel streams of this coax signal to support 705.6/768kHz sampling rate. A coax audio signal is one-way, one wire (plus ground), self clocking and simple to decode (being developed in the 1980's).
Yet, since it is a galvanic connection, S/PDIF coax is a conduit for RF noise. When the MScaler dual-coax hardware upsampler was introduced, AudioWise developed OPTO•DX using all-analog optical modulation. This provided immunity to RF noise with a perfect 100MHz bandlimit and is a much better approach than filtering using ferrites on the cable. Recently, DC•BLOCK Version2 was developed to filter any DC leakage current and provide supplemental filtering at frequencies below 1MHz.
So while the combination of OPTO•DX + DC•BLOCK is the best way to get high resolution to a DAC, the market for SRC•DX was looking for a lower priced alternative to OPTO•DX. AudioWise is pleased to announce LP•FILTER, an inline coax filter that gets you 80% of the benefit of OPTO•DX at 40% of the cost. As per the drawing below, you can see that both approaches filter the same frequency regions - with OPTO•DX having a sharper dropoff and the inherent benefit of optical isolation
For more information, please view the DC•BLOCK/LP•FILTER product link here.