The comment made by
@HissingFree is well said. In my view, the kind of test that needs to be added to a conventional suite of tests is an analysis of dynamic, not steady-state, signals over time. A spectrogram analysis of a level-changing multitone signal, shown in my review, is such an example. Although this analysis was used to show the DRE artifacts, I believe it makes sense to include such a test in a standard 'battery of tests' for the purpose of checking any potential issue of a similar kind.
For example, I created a test signal made of 11 tones concentrated in the bass region, whose FFT looks like:
View attachment 465900
Then added fade-in and out effects (-50 dB through -3 dB) over time:
View attachment 465901
Here's a spectrogram of this signal played by the Black Pearl w/ its
Fast-LL filter (i.e., DRE enabled):
View attachment 465904
DRE-induced distortion is nasty.
Of course, distortion is gone in
NOS mode of the Black Pearl:
View attachment 465905
But do you know what is surprising? According to
this spreadsheet, some CS431xx-based devices exhibit limited DRE artifacts, which I suspect to be attributed to an adjustment made by those DAC manufactures on some DRE-related parameter in the chip (likely
'DRE decay rate'). For example, DRE artifacts of the following devices
- Fosi Audio DS2
- JCally JM20
- JCally JM20-Max
- A few more devices
cannot be detected by steady-state multitone tests. In fact, the
C Major test signal is an ideal test signal. For instance, note that the above test signal simply keeps increasing its level and then keeps decreasing it; that is, it's just one cycle. In response to this signal, these devices behave surprisingly nicely. For instance, the spectrogram of the signal played by the
JCally JM20:
View attachment 465906
shows nearly no distortion (yes, nearly; we see a faint sign of it by zooming the plot).
Lastly, see below spectrograms of some music played by the
Black Pearl with the Fast-LL filter (DRE enabled) in the upper panel and
JCally JM20 in the lower panel:
View attachment 465907
Note that I just picked a random song (i.e., did
not choose this particular song to show large distortion effects). I did not choose this song to tell something about the distortion's audibility, either. Just to compare the two devices' different behavior.
As you can see, the distortion is much less frequent for the JM20. I bet this would not be audible since in most cases it should be masked whenever it overlaps with a wide frequency spectrum in audio content.
In fact, as suggested by the measurements in the "
Other Characteristics" section of
my review, the reason why the JM20, or another device showing the same behavior, does not distort is simply because DRE is not fully active much of the time! Whenever the signal level reaches a strong level, DRE becomes inactive, or does not increase its effect. It simply
waits, or just wants to decrease DRE gain if the signal gets stronger. Only after the signal goes below -50 dBFS, it turns the DRE back on. This is very passive DRE.
I would call this a good, albeit minimal, DRE implementation. Then, the question is, did the designers of these devices deliberately adjust this DRE parameter for this effect? I absolutely have no idea.
github.com
www.head-fi.org
but it is not this device faut)
