Solving the Mystery of Inverted Polarity on My PC

Introduction

For weeks, I was dealing with a strange issue: my IEM measurements were showing inverted polarity on my PC (and it sounded like it), but everything seemed fine when I used my laptop. After countless tests and troubleshooting, I finally discovered the cause and the solution. This post breaks down the entire experience and how I figured it out.

First Clues: The Inverted Polarity

The problem started when I used my usual measurement setup: a 711 coupler, REW software, and a DAC/Amp connected to my PC. The results showed inverted polarity on almost all IEMs, which didn’t match reports from other users. However, when I ran the same test on my laptop using the exact same equipment and settings, the polarity was correct.

This led me to suspect the issue was with my PC, not the IEMs or the DAC/Amp.

Testing and Finding the Problem

To rule out other variables, I ran additional tests:

• Connecting directly to the PC jack: I used the integrated audio output on the motherboard instead of the DAC/Amp, but the polarity was still inverted.
• Microphone check: To verify if the microphone signal was inverted, I connected a 3.5mm-to-3.5mm cable, plugging one end into the microphone jack and the other into the headphone jack of the same PC (without a DAC in between). Then, I ran a sweep in REW to evaluate how the motherboard’s sound card behaved. The measurement appeared as a straight line, as expected, but when I checked the phase tab, I noticed it was inverted (I obtained the same result connecting the 3.5mm cable in the DAC/Amp in the different USB ports).

This confirmed that the issue was how the motherboard processed the microphone signal, which affected my measurement results.

The Solution: Unifying the Signal on One USB Port

Finally, I decided to connect both the microphone input and the headphone output to the same USB port using a dongle dac, ensuring they shared the same signal reference. With this setup, my PC measurements matched those from the laptop, confirming the problem in my PC's jack. When performing measurements across all my USB ports, the polarity was correct in every case.

Additional Issue: Front USB 3.0 Ports

Even though I knew my measurements had been correct all this time, I noticed something odd: when using the front USB 3.0 ports on my PC, the sound seemed different. While REW measurements showed correct polarity, I could still hear something unusual.

Just by listening, I noticed that while most ports sounded fine, the front USB 3.0 ports still exhibited inverted polarity. Once again, this discrepancy was identified solely by ear, without any measurements.

I have an IEM where I can easily detect when the polarity is different. I confirmed that the polarity was consistent across my smartphone, laptop, and the rear USB ports on my PC. However, when I connected the DAC/Amp to the front USB ports, there was a significant change in the sound. So, reversing the cables on any of my other devices produced the same sound as when using the front ports on my PC.

This explained why my IEMs sounded good when using reversed cables: I had been using the front USB ports all along! (which introduced a signal alteration). When I switched to the rear ports and connected the cables correctly, the sound behaved as it should.

Problem Solved!

Conclusion

After weeks of research and testing, I discovered that:

• The issue wasn’t with the IEMs or the DAC/Amp.
• Separating the microphone and audio output signals caused polarity discrepancies in my measurements (mainly due to hardware problem).
• The front USB 3.0 ports on my PC affect the sound in some way.

Definitive Solution:

Use an external PCIe Express USB 3.0 card.

Now I will name my models with reversed polarity: KZ brand, QKZ brand, Tangzu Wan'er, CVJ Konoka, Truthear Zero:RED, Letshuoer S12 Pro, Hakugei Anunachi.

I hope this experience helps anyone facing a similar problem.

Thanks for reading!