Post by WombatI don't know how you create these pics. If you do it with DAC output you
should make sure no further resampling is done and for comparison it
should be nice to see both results with SoX, one with dither and one
without. Maybe this hints to something. Sorry if that makes you busy
only because i have a wild speculation.
edit: didn't see your edited post, was typing to long on my pad...
The pics are snapped from real-time FFT done from the direct RCA capture
of the DAC output through the E-MU 0404USB at 24/96. No resampling or
DSP engaged... Just spectrum analysis of what's coming in.
Tonight, as I look into this, I realized just how complicated it's
getting and how hard it would be to show the pictures unless this was
one of my long blog posts! Bottom line:
It really depends a lot on the resampling algorithm and obviously
hardware!
It looks like *both* integer resampling and dynamic headroom have a part
to play in the square wave tests at 0dB.
IN SOFTWARE: If you do integer resampling on 0dBFS like 44kHz --> 88 -->
176, Adobe Audition, and dBPowerAmp maintains the clean harmonics.
SOX for some reason is not giving me the same result! Not sure if it's
because Audition and dBPowerAmp are anticipating and upsampling with a
small amount of volume overhead adjustment.
IN HARDWARE: Using the TEAC UD-501, integer resampling is not a problem
- for example 48kHz --> 192kHz results in a nice spectrum. Likewise the
ASUS Essence One "symmetric upsampling" was not a problem. However
non-integer 44kHz --> 192kHz results in the additional harmonics I
showed last night with the Teac; presumably similar to the DAC1 pictures
from Ken Rockwell.
Now as for volume headroom - YES, this does result in cleaner harmonics
including SOX even with non-integer upsampling from what I see using
SOX, Audition, and dBPowerAmp. Therefore, Darren / Benchmark is right to
allow headroom while upsampling - avoidance from clipping is never a bad
thing!
I couldn't see a difference with dithering since this was upsampling
from 16 --> 24-bit which is logical when I tried SOX (both dithered and
undithered looked nasty going from 44 --> 192)...
In any case, as you can see, the situation looks complicated and it'd be
tough to put together images of the combinations I tested.
Bottom line, and I think the *only graph* that would be of benefit for
Benchmark DAC1 owners is one where a -3dB 1.00227kHz square wave is
passed through the DAC1 and there's demonstration of a clean 1kHz
primary with the appropriate clean 3/5/7/9...kHz harmonics to show that
the volume reduction helps. Based on my TEAC UD-501, it should look like
this:
-3dB Square:
14796
-3dB Square upsampled to 24/192 by Teac:
14797
Nice and clean with minimal even order harmonics...
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