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Old 03-06-2019, 06:23 PM   #1
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Default [SOLVED]Very strange: sound frequency response changes through DisplayLink

Until here, I'm quite happy with my lenovo Helix 2, its ProDock connected through USB 3.0 to my monitor.
Until I noticed that the sound was changed, very much so, compared to exactly the same monitor (with speakers) on that same input, fed from the micro-HDMI port. While the sound from that micro-HDMI port sound like High Fidelity, the sound through the USB 3.0 and the ProDock and finally through DP has a frequency range of very few bass, strong mid range and also reduced high pitch volumes.
In short: like through an equalizer set to render speech better.
In here I found that DisplayLink has no equalizer, I also found no equalizer in the ProDock.

Now I am really curious where those alterations are actually effected? On the long run, I don't want to miss on a high quality sound through my monitor speakers. So I wonder where that equalizer function is actually done, and how I can prevent it from happening?

Just to be very clear: There are no clicks, no harmonic distortions. I have checked my Ubuntu 18.04, and there is no equalizer installed, the Pulseaudio doesn't show any. And if, then the sound through micro-HDMI should have undergone the same.
I just plug/unplug the two cables in the same monitor input, and switch the outputs from USB Pro Dock to HDMI in the Pulseaudio applet, so that the sound can be heard. And that makes a big difference.

Last edited by udippel; 03-18-2019 at 02:57 PM. Reason: Solved
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Old 03-18-2019, 03:06 PM   #2
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My ears didn't fail me.
I found the reason: In Pulse Audio Volume Control I happened to notice that the USB 3.0 Pro Dock Sound drain was set to Analog Duplex in Configuration. So it was D/A-converted for the headphone socket, and re-converted D/A to be sent to the monitor via DP. The very moment I set it to Digital Output (S/PDIF) it was okay.

As an aside, though solved here, this still looks like a hardware circuit design failure through the analog signal path, since any proper analog circuitry will not effect the frequency response audibly through this type of conversion.
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sound frequency response

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