Finally got around to measuring the Topping D90SE and Gustard X16 filters in the stack setup. Here's the amplitude response for the seven different Topping filters:
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The colors that REW ended up picking are not great, but these are in order, from top to bottom:
- Mode 1 - Fast roll off apodizing
- Mode 2 - Slow roll off minimum
- Mode 3 - Fast roll off minimum (default)
- Mode 4 - Slow roll off linear
- Mode 5 - Fast roll off linear
- Mode 6 - Brick-wall
- Mode 7 - Fast roll off corrected minimum
Here's the same plot for the Gustard's three filter choices:
View attachment 155338
From the plots, it's clear that this is a proper subset of the Topping filter options:
- L-FAST (same as Mode 5 - Fast roll off linear)
- M-SLOW (same as Mode 2 - Slow roll off minimum)
- H-FAST (same as Mode 7 - Fast roll off corrected minimum)
I'll just compare the time-domain response of these three, but if you're interested in looking at the others, feel free to download my REW *.mdat file
here.
Here's Topping vs. Gustard (in that order) for Fast roll off linear / L-FAST. I'm showing the step and impulse response. For these plots, I'm looking at the length and degree of pre/post-ringing:
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View attachment 155340
Not identical, but pretty darn close. Here's the same for Slow roll off minimum / M-SLOW:
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Finally, here's Fast roll off corrected minimum / H-FAST:
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Not sure how audible any of this stuff is, but of the three, H-FAST (Mode 7 on the Topping) appears to have no pre-ringing, while post-ringing is not terrible. From what I understand humans tend to be more sensitive to pre-ringing (which does not occur in nature except on Star Trek) than post-ringing, so this seems like a reasonable tradeoff.
At the end of the day, you get to choose which you prefer if you have one of these DACs. Again, feel free to download my
REW data file to see the rest of the Topping filters. If you want to use my limits settings to match the captures here, select "%" instead of "dBFS" on the "Impulse" tab and use these limit settings:
View attachment 155348
For the rest of my listening, I'll leave the Topping on Mode 7 and the Gustard on H-FAST. The amplitude response looks funky (when zoomed in), but I can't hear to 20 kHz anyway, so a half a dB of roll-off at 16 kHz doe not bother me in the least. Enjoy.
Edit: I've fixed the zip file containing my REW *.mdat file. Did this late last night and mistakenly used `gzip` instead of `zip`. Sorry. Also, I created these plots using the latest
beta version of REW. I've not tested, but I would not be surprised if the
production release of REW fails to open this file, which kind-of sucks. It only takes a few minutes to create an account on
AV NIRVANA so that you can download the beta, but sorry for the inconvenience.