fix outcentered audio track

2021-03-05 09:56:55

Hi,
I didn't know how to title the question, as never experienced such a case.

I have a sound track see attached picture, which:
1/ obviously the first 2min have been added to the rest, so it is easy to split the audio in 2 files.
2/ the audio after 2min seems off balanced, non centered, in wave display.
As such it prevents from normalizing the track, see attached pic.
What can I do to correct that?

thanks

Re: fix outcentered audio track

Reply #1 – 2021-03-05 10:47:07

It is likely an asymmetrical waveform, which is naturally produced by some brass and bowed instruments, and human voice. Ocasionally happens with synthesizer patches too. You could rotate the phase to center it. There are tools in Reaper, Izotope RX channel operations and Stereo Tool for that. But you will need to squish it with a limiter afterwards as there will be some high peaks left over.

It could also be a low frequency vibration. I can't tell from the zoomed out screenshot. But unlikely. You can attenuate that with a highpass filter.

Re: fix outcentered audio track - asymmetric waveform

Reply #2 – 2021-03-05 11:04:34

>It is likely an asymmetrical waveform, which is naturally produced by some brass and bowed instruments, and human voice.
It's pure human voice, not the single instrument

I presume sthg went wrong with the voice recording

Asymmetric, that's the word I think. If one looks at the track, the "zero of the wave" is put to "high"

>You could rotate the phase to center it.
What does it mean??

Re: fix outcentered audio track

Reply #3 – 2021-03-05 12:00:36

Use a plugin such as Audication Phase AP1 (free) and try different values around 90° and see how they affect the peaks. In Izotope RX there are modes (suggest and adaptive) that can determine the amount needed to minimize peak level. You could gain 1 or 2 dB of headroom, but there will probably be peaks reaching both positive and negative limits. I do not know what kind of filters are available in your software. All-pass filters in an equalizer could also be used. These all will subtly affect the sound.

This waveform is not "wrong". It's a characteristic of the sound source. In broadcast radio a phase shift is sometimes used on voice to maximize loudness.

Re: fix outcentered audio track

Reply #4 – 2021-03-05 12:38:19

I must say that your answer is too complex for my present level of comprehension.

What I hear from this old speech, is that it's not loud enough.
Normally, what I would do is to normalize the track, or amplify portions by portions the track.
But in this case, I can't because it's overclipping.

Googling I found https://www.youtube.com/watch?v=6iF7-_L4fgs
it explains from 01:30
the question is how you fix this, without changing the sound, make it more symetrical without affecting the sound?
and indeed speaks about "phase rotation" solution.
but presently don't know what to put in, because I neither understand the "phase rotation" effect, nor what's the solution, the goal/target.
https://manual.audacityteam.org/man/phaser.html

Re: fix outcentered audio track

Reply #5 – 2021-03-05 13:59:02

The linked video tutorial describes exactly the process I was thinking about. I'm not sure if a clean rotation can be achieved with Phaser. Maybe a user of Audacity can respond.

If you want to increase the loudness significantly, then you should use a Compressor and a Limiter anyway. It will automate the amplification of quiet portions. The potential gain from centering the waveform won't be enough.

Re: fix outcentered audio track

Reply #6 – 2021-03-05 15:23:53

Like j7n says, some voices are naturally like that but your case looks "worse" than I've seen.    Or it could be an issue with the microphone or preamp, especially if you are using the mic built into a laptop or a regular consumer soundcard.   

A high-pass filter is worth a try.   A 100Hz high-pass filter won't affect voice frequencies.

Limiting will help because it will knock-down the stronger negative peaks first.   And, it will be louder when you normalize.


...It's NOT a "DC offset" problem.    DC offset (caused by a hardware defect) is similar but silence is also shifted.  There are DC offset removal tools which will probably make your waveform more centered but if you have an asymmetrical waveform that can actually create a DC offset (depending on the algorithm) which is a worse problem...   You can't hear DC (zero Hz) but If there is silence at the beginning or end you get a "click" when the offset suddenly kicks-in and kicks-out.