Filter brewing for the Soekris R2R


Have only just ordered my board, bit slow on the uptake, have been looking about, is there a way to just play music with the original sample rate and not use the upsampling in the DAC FPGA?

From what I have read the "NOS" filter still uses the upsampling side.

Whats are the options here please? Have tried searching but haven't found a search term that answers my question yet.

Thanks in advance,



2010-10-04 11:03 pm
Short answer is "no". You need to let the FPGA do its job in order to drive the R-2R ladder. That constitutes upsampling.

The "NOS" filters bypass the "first stage" of upsampling, but there is no way to bypass the "final stage".

There are sets of filters like the one I have configured, or the one of Bambado, that have the F7 NOS filter in both the FIR1 and the FIR2 filters. Then, selecting F7, behaves like an authentic DAC NOS without oversampling. The "final stage" second oversampling behaves in that case just as the first oversampling, it take F11 NOS filter, does not perform oversampling. And it can be verified with an oscilloscope.