Hi @smazumder
Simon has summarised the situation in his post. Just to fill in the full picture of the how and why:
- On the Burr Brown DAC’s they can be configured into an external oversampling filter mode, which means we feed either 705.6 or 768kHz dual channel I2S data at the DAC, which directly drives the sigma delta modulator.
- When doing PCM we run a 21489 SHARC to do a custom over sampling filter that has far superior capabilities then the oversampling engine built into the DAC’s. It uses about 40% CPU time on a 2GFlop DSP, so it’s doing some serious number crunching.
- When doing DSD mode we do a single step DSD bit stream to 705.6kHz conversion so the data is direct to feed to the modulator. Hence avoid multi stage conversion, where every digital filter will not be totally transparent.
So why not just feed the DSD straight into the DAC? In practice the internals of the Burr Brown DAC (and all dacs) are built at a cost and the performance of the DAC’s DSD support (+ external analogue components to filter off the HF noise inherent in DSD) is not as good as using the DSP. It also compromises PCM mode.
Overall the power of a SHARC running Naim custom DSP code, a great clocking circuit, the Burr Brown DAC running in external over sampling mode, plus living in a very nice electrical environment and a top notch analogue output gives very competitive results.
Best wishes
Steve Harris
Software Director
Naim Audio Ltd.