Let's Settle this DSD BYPASS mode on AKM chipsets once and for all!

​The S.MS.L D400 PRO DAC is in lab at Euphonic Review and it mighty impressive, I must say.
This will be the second DAC I have reviewed with the latest AKM chipset... the AK4191 + AK4499 (not to be confused with the older AK4499 chip).

The first DAC I reviewed (which was a very fine DAC) making use of this latest AKM silicon was the Topping E70V 'Velvet'. A fine sounding DAC in its own.

Unfortunately, I started to see lots of really lazy reporting regarding its native DSD, or lack of native DSD implementation. The Topping allows for a fixed output, as do many a DAC. For some reason, otherwise gifted and respected reviewers gloss over the fact this does NOT mean the chipset uses its 'bypass' mode for native DSD.

The Topping E70V offers no choice of DSD filter (it has a single preset, non-changeable FIR filter at 19khz for DSD64 files). Nor does it offer any use of the volume/Delta Sigma Modulation Bypass mode. Simply being in fixed output mode does NOT bypass the Modulator. This was my own observation after studying DSD and its various implementations for years, plus I confirmed this directly with an engineer at Topping. Certainly you can set the volume control at full output for either format as such it has a 'fixed' output. However, for DSD the Delta Sigma Modulator is still in use and cannot qualify the DAC as true native DSD.

Not so the case for the AKM chipset as implemented in the S.M.S.L D400 PRO. It has THREE distinct output modes, as well as access to both 'WIDE' and 'NARROW' DSD filters. According to the manual (which while not great is better than anything I have seen from Topping), the THREE PRE-MODES are as follows.

This is lifted directly from the manual--

* VARIABLE ---- The output is volume controlled. (all formats)
* FIXED ---- The output volume is fixed. (all formats)
* FIXED DSD BYPASS ---- Open the DSD direct access/bypass function. At this time, the volume of PCM or DSD in NOT adjusted. The output amplitude is fixed to about 3.7VRMS. When this function is opened, the DSD is NOT processed at all, and the output is directly output.

Now that this small detail is settled once and for all (well, it SHOULD be settled, anyway) I am looking forward to a weekend of listening comparing the D400 PRO with its little brother D300 with the ROHM chipset, as well as compare it to the RME ADI-2 PRO, while yes, having the older AK4493 chipset, has a similar activatable DSD modulator bypass mode as well. And finally, I am always interested in how it stands up to my favorite DAC of the last half-decade... the iDSD PRO.