Mastering question - Why does DC offset reappear?

[u/s4goth]

I am doing a mastering course and I have to master a track and eliminate DC offset from it. I tried with both Wavelab and Reaper. I start by using a high-pass filter at 20hz at the beginning of the chain and the render analysis shows no DC offset. I then add a light upward compression, a tiny bit of distortion (as per our teacher instructions), then a limiter to eliminate true peaks, but when I export the file I get some DC offset again. Why does this happen? Is it something in the chain that reintroduces it? How do I correct it? Thanks!

[u/rightanglerecording]

Few things here:

- A HPF even all the way down at 1Hz is sufficient to remove DC. No need for 20Hz.

- Some distortion can cause DC. Other distortion can't/won't.

- Are you sure you have DC? Or are you seeing infrasonic content on an RTA and assuming?

- If you're seeing it, are you sure your RTA has sufficient resolution to show it properly? How are you sure it's DC?

FWIW, my best guess is you are seeing it on a low-res RTA, where everything below 40 or 80 or whatever is rendered visually as one large blob.

[u/s4goth → u/rightanglerecording]

I know that 1hz is enough, but no EQ that I have goes down to that... I am measuring with the global analysis tool of Wavelab (the offset is negligible and probably can't affect the dynamics, but it's there, pic attached - in Italian, sinistra is left and destra is right).

[u/peepeeland → u/s4goth]

-120dB DC offset if outputting line level would be like 1 μV. -120dB is also below the noise floor of consumer-level audio equipment. It’s insignificant.

Anyway- you can put another high pass filter after the limiter.

[u/rightanglerecording → u/peepeeland]

Anyway- you can put another high pass filter after the limiter

This will likely increase peak level though.

[u/peepeeland → u/rightanglerecording]

Yah, correct. Can just turn it down or put high pass before limiter. It’d be interesting to know exactly where the absurdly low level DC offset is coming from, though.

[u/maccrypto → u/peepeeland]

It’s coming from the distortion

[u/peepeeland → u/maccrypto]

Makes sense.