KVR Audio

MaxC · Post by **MaxC** » Sun Sep 04, 2011 5:30 am

I was working on mastering a mixdown today and noticed a fairly obvious asymmetry in the waveform. At first I assumed it was DC offset, but analysis revealed only a minimal (0.12%) offset. I removed it anyway just to be sure, and even after dc offset removal, the asymmetry remained. I tried to locate the source of the problem by rendering one effect unit at a time and discovered that the asymmetry did not exist until the mastering EQ (which was set to minimum phase).

The resulting sound file still sounds normal, but I'm worried about how this asymmetry will affect subsequent processing, particularly limiting. When I limit the EQ'd file, you can see the negative half of the waveform is being squashed more than the top half. I don't notice any unusual artifacts when listening, but I'm skeptical that limiting the waveform in this manner is advisable, if for no other reason than that I'm losing headroom due to the asymmetry.

Is it usual for a minimum phase EQ to produce such an asymmetry? There are some pretty sharp cuts and boosts, and I notice the problem disappears when I use linear phase mode instead, so I'm quite sure the issue is related to the use minimum phase (the sound of which I typically prefer). Ideally I'd like to stick with minimum phase, so long as I can rest assured that there is nothing "wrong" with having a waveform preferentially limited toward one pole more than the other. Can any of the technical gurus out there advise as to whether this is a normal occurrence and if it is indeed problematic?

Thanks in advance.

Loki Fuego · Post by **Loki Fuego** » Sun Sep 04, 2011 9:20 am

Any non-linear phase EQ introduces phasing issues. If you want to keep waveform unaltered then only linear phase EQ is the only way. But I don't really think you should worry about the way waveform looks. If it sounds good, then it sounds good.

lfm · Post by **lfm** » Sun Sep 04, 2011 9:30 am

If looking at what tubes do to waveforms - it adds assymetry. It add harmonics in an assymetric way.

So maybe part of what you process in mastering stage include exciter or similar that adds tube warmth.

dalor · Post by **dalor** » Sun Sep 04, 2011 11:55 am

Especially if you cut with a low pass bass heavy sounds with a non linear eq the asymmetry seems to increase and steals headroom.

MaxC · Post by **MaxC** » Sun Sep 04, 2011 10:22 pm

dalor wrote:Especially if you cut with a low pass bass heavy sounds with a non linear eq the asymmetry seems to increase and steals headroom.

I do believe you are correct, dalor. I had a pretty steep rolloff in the subsonic region which, when mollified, reduced the degree of asymmetry. The top graphic you included pretty well illustrates what I was experiencing. Now I'm left wondering whether tempering the rolloff will offer more or less headroom than simply living with the asymmetrical waveform... Gotta love the nuances of audio production

.

camsr · Post by **camsr** » Mon Sep 05, 2011 4:12 am

Mute your stems one by one and look for the asymmetry to disappear. On that stem, use an allpass filter and adjust it while metering the master bus. Listen and compare. Or stick with the linear phase which is probably just as well. The only change is pre and post ringing which might go unnoticed.

deleted · Post by **deleted** » Wed Sep 07, 2011 11:41 pm

DELETED

dstar1 · Post by **dstar1** » Fri Sep 09, 2011 9:26 am

are you the max c as in the greatest singer of current house music?

if so you are my hero.

IIRs · Post by **IIRs** » Fri Sep 09, 2011 10:05 am

MaxC wrote:Can any of the technical gurus out there advise as to whether this is a normal occurrence and if it is indeed problematic?

I would say that if you can get your mix up to your target RMS levels without excessive limiting, the asymmetry is not a problem.

Is it normal for EQ/Filter to introduce asymmetry in the waveform?