Above the centre line not equal to below

Hi Folks,

I’m a beginner, with not much knowledge about audio, as a result I don’t know the “name” of my problem so I can’t search the Forum for answers. I have looked at the FAQ and not found anything to help.

Running Audacity 2.3.2
Windows 10 version 1903 (Build 18362.175) 64 bit

I have a mono audio book where the playback volume (on max) is not great so I wanted to “Normalize” it to help.

On loading the files into Audacity, I see that they are heavily distorted with peaks above the centre line reaching approx 0.7 to 0.8 while below the centre line, peaks never go beyond -0.5.

The DC offset is not the problem, the centre line is perfectly set on 0.
audacity 1.jpg
Please can anyone tell me if there is an Effect to correct this



An asymmetrical waveform is not necessarily a problem.

Audcaity’s (soft) limiter (say -6dB) with make-up gain enabled.

An asymmetrical waveform is not necessarily a problem.

It’s “unusual” for an audiobook.

I have a mono audio book where the playback volume (on max) is not great so I wanted to “Normalize” it to help.

This is an audiobook you downloaded, right? If this is something you recorded yourself, you might need some better equipment…

A high-pass filter (maybe around 50-100Hz) should even-out the waveform without affecting the sound. Then, you can normalize for a higher peak-to-peak waveform. That’s the same idea as the DC offset correction, but you don’t have DC offset. DC offset also shows-up during silence.

Yes it is a file I downloaded. It is a book from 1961. Not sure when the audio version was created
. I’ll have a look at these solutions though. .many Thanks

Much appreciated help. Very prompt and helpful. Thanks

Many thanks. In my specific case, I believe the High pass filter gave the slightly better result, but in reality there was little (real) difference.

Thanks again


I’m with Trebor. I don’t think that’s broken.

Production that old would have gone through vacuum tube amplifiers. In the same sense that someone today would buy a “Professional, Studio, Broadcast” microphone for $26, Inexpensive, affordable sound systems existed back then as well. It’s perfectly normal for vacuum tubes (“Fire Bottles” in the trade) to have distortions like that. It’s one of the reasons I think you can still get tube guitar amplifiers or aggressively modern amps with that “robust tube sound”—sometimes on a switch.

Tube Sound ON/OFF

I would stop trying to fix it.


OK I will have a listen to before and after and see what I think.

Just done a bit more digging though and I believe that although the book dates from 61, the audio version looks to be early 2000’s.


It’s a good head exercise assuming you insisted on fixing it, how would we do it.

It’s super unusual to have filters, effects or corrections that only affect one direction of the waves.

I think I could do it if there was a way to intentionally add DC offset. DC Offset is normally evil (a broken microphone for example), so there are common tools to remove it…

As was posted several times already, the show does not have DC Offset or any other common unbalance, so any corrections would have to fix the waves, sound good and not damage anything else.

You sure you want to mess with this? This could be a career move.


This is me on a recent sound test. See, I’m not symmetrical, either, but it’s not terrible and I sound just fine—given that it’s me and all.

Screen Shot 2019-07-05 at 19.42.32.png

Actually, that’s a good illustration how this works. This is a blowup of the sound at 1/2 second.

The red bar (lighter blue) is the RMS or approximate loudness and it’s more or less even. The green bars are the peaks, tips and waveshapes and they are profoundly uneven. That’s how I speak. I did nothing unusual to shoot that.

If you started with a wispy, thin voice, I can imagine that most of the wave might be uneven.


I must admit I simply assumed that because it was asymmetrical, that it must be wrong. Knowing so little about audio, it seemed the obvious conclusion.

Having listened to it again, the original file does sound acceptable. The converted file also sounds acceptable. There is a difference, but not a massive one. Is one better? Hard to say. Which one is nearer to the original? I’ll never know.

So I’'ll probably leave the files as they are and not waste time correcting a problem that I thought was a a problem, but probably wasn’t.

However it was a useful exercise in that I learned a bit, and that is always good.

Thanks to all. This is what a forum should be. Help, not antagonism.