These are the orders of the SDM filters. foo dsd asio only uses SDM 5. But higher ones exist.
I've done some more testing on the SDM settings today.
Only the 1k Sine with MTA but maybe I'll test something with the MT32 test as well later.
I used foobar2000, HQPlayer and Audirvana for playback.
First, it's important to note that the SDM filter type or order doesn't matter if you are playing native DSD.
The DSD data is sent as it is to the DAC, hence there's no reason to care about it.
This is the native DSD256 output of the Aune X8:
It's always exactly the same at a given rate for foobar2000, HQPlayer with DirectSDM or Audirvana without resampling.
Where it matters is for PCM or DSD conversion to DSD.
I'm not really sure if adding more coefficients is so much of an advantage or not.
If the ADSM5/ADSM7 on HQPlayer really means 5th/7th order, doesn't look like there's much if any difference at least on the ESS DAC.
What matters is the filter type and if it's Clans or not.
But even there seems to me Clans is a little worse and Type B is slightly better than D.
This is foobar2000 DSD256 SDM Type B:
And this is foobar2000 SDM Type D:
This is foobar2000 SDM Clans 4:
This is foobar2000 SDM Clans 7:
HQPlayer is always a tad better at the expense of 3dB SNR:
Audirvana also as a very similar, almost 100% copycat, output converting PCM to DSD:
I was really curious to test Audirvana as it offers both a custom SoX resampler and r8rain for resampling to DSD.
Lots of customizable options for the filters.
It was a bit of a disappointment.
First, Audirvana is not capable of doing any DSD to DSD conversion.
Which means that the "better" output similar to HQPlayer is limited to PCM content.
Would have been nice to have the option.
Second, all the conversion settings for SoX or r8rain are producing a very similar output.
This is a PCM conversion to DSD128 with r8rain Filter Type A 5th order:
And this is a PCM conversion to DSD128 with r8rain Filter Type B 5th order:
You can see a very slight change on the HF noise shape but that's all.
This is a PCM conversion to DSD64 with r8rain Filter Type A 5th order:
And this is a PCM conversion to DSD64 with r8rain Filter Type B 5th order:
Here the difference is a bit more visible.
Going to 256x rate and up it's impossible to spot any change.
I mean, the output is very good in any case but event at DSD64 rate there isn't probably any audible improvement whatsoever.
foobar2000 DSD Processor impact of filter type is much less subtle, this is conversion of PCM to DSD128 Type B:
And this is the foobar2000 DSD Processor conversion of PCM to DSD128 Type A:
The DSD Processor output seems to have much less noise filtering but it's also not attenuated by 3 dB.
And anyway almost all this delta is at -120 dB or below.
Another question I was asking myself was if it was worth upsampling DSD64 to DSD128 or higher.
You can't do it with Audirvana and it's definitely a good idea with HQPlayer.
With foobar2000's DSD Processor is a resounding no.
The DSD Processor is quite decent with PCM but it's awful with DSD to DSD conversion, this is DSD64 to DSD256:
It's better to avoid any kind of conversion, unless really needed for rates which are not supported natively.