Having set up DRC using a RPi with HiFiBerry DIGI2 Pro + DSP card, I
have an issue.
When setting it up (having used REW to calculate the required filters),
I was of course using source material with significant bass content to
audition the results, and pleased with the way it tamed the bass humps
in the room.
But once I started listening in earnest, noticed some curious low
frequency artefacts during quiet moments, a kind of grumbling that
varies in amplitude. The closest analogy I can give is that it sounds a
bit like turntable rumble. Thinking I might be imagining it, I tried
playing something while toggling the filters on & off, and the artefacts
are definitely only present when the filters are active. It's quite
subtle and only at very low frequencies. I can't hear it on (admittedly
inexpensive) headphones, only on my active Meridian speakers.
The filters are fairly extreme, with some significant gain settings and
high Q:
Code:
--------------------
Filter 1: ON PK Fc 54.3 Hz Gain -19.2 dB Q 2.831
Filter 2: ON PK Fc 71.1 Hz Gain 9.0 dB Q 3.982
Filter 3: ON PK Fc 75.2 Hz Gain -5.4 dB Q 7.677
Filter 4: ON PK Fc 89.3 Hz Gain -5.5 dB Q 11.271
Filter 5: ON PK Fc 148 Hz Gain -13.3 dB Q 13.429
Filter 6: ON PK Fc 202 Hz Gain -6.2 dB Q 5.000
Filter 7: ON PK Fc 225 Hz Gain 6.3 dB Q 5.000
--------------------
My question for the experts here is whether these kind of grumbling low
frequency artefacts are a known issue with DRC.
Perhaps they are to be expected with such extreme filtering?
Maybe the code that HiFiBerry uses to implement the filters isn't as
good as it ought to be?
I'm in a bit of a quandary: with the filters turned on, the bass
response is nice and smooth, but now I've heard those artefacts, they
are impossible to ignore. With the filters turned off, the bass has some
pretty obvious humps that I would like tamed.
Until recently: Transporter -> ATC SCM100A, now sold :-(
House move forced change to: SBR SPDIF out -> Meridian 218 -> Meridian
M6
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