Restoring audio quality on Windows, part 2

Headphone jacket on a laptop

The following is not a recommendation for action. I take no responsibility for any malfunction of your device.

It is with annoyance that I find myself again with a new Windows laptop which delivers an unbelievably terrible headphone sound. Listening with a Beyerdymanic DT 1770 PRO, it sounds as if the sound comes out of a kitchen radio from the late 80s (to be fair, there also were quite decent ones back then).
Yes, yes, I know that built-in headphone jacks are usually not meant to be used with headphones with such a high impedance. But this travesty is not a matter of insufficient hardware, but software algorithms in the form of Windows APOs (Audio Processing Objects) that are there to “enhance” the sound of the laptop speakers. But someone has forgotten to set it to turn off when headphones are plugged in. And to be honest, even the built-in speakers sound much worse with this filter.

I have made this experience before already on 3 laptops: An HP ENVY, a DELL Latitude and an ACER Aspire. There is a post in which I have documented how to disable the sound processing with two of those, but these things change quite regularly. This time, number 4, it is a cheaper one, an HP 14.

So I started digging again for things that could be disabled or deleted in order to get a normal, i. e. linear sound again. This time it was not as easy as deleting some files in C:\Windows\system32\, because I did not find any DLL file with a suspicious name like “BadSoundFilterAPO.dll“.

Then I took a look in the Windows registry editor. Searching for “APO”, I found HKEY_CLASSES_ROOT\AudioEngine\AudioProcessingObjects\ which was full of APO registrations. I disabled one that I found particularly suspicious, because it was neither by Microsoft nor by the soundchip manufacturer Realtek, but by a company called “Sound Research Corp.” I decided to mess with it by changing the last character of its UUID from a 7 to an 8 in the hope to break a reference to something. I rebooted the PC and voilà, the sound was normal again. What a lucky shot!

We’ll see if the bad sound comes back after the next Windows update (just like it did with the other laptops) and I have to do it again.

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