Does this look like LFO DC offset??

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Does this look like LFO DC offset??

Post by dfira »

Hi guys,

I noticed over some recordings that I sometimes experienced some DC shift, and sometimes it was not present.

I know that for some reason brass instruments tend to push the waveform off to one side, but that is a static shift, not a constantly changing one.

But in my vocal recording it kept changing, so I tried to record a loud sound for as long as I could hold my breath and this is what I saw:

Image

Do I have an electrical fault?
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Re: Does this look like LFO DC offset??

Post by Hugh Robjohns »

No. Asymmetrical waveforms are very common.

If it sounds alright, it is alright. Don't let your eyes deceive you into imagining non-existent faults!
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Re: Does this look like LFO DC offset??

Post by James Perrett »

Real DC offsets rarely exist these days (though it was a real problem with my first soundcard 30 years ago).

All you are seeing is another example of an asymmetric waveform. Vocal waveforms are often asymmetric. Try zooming in and you'll see large short positive going spikes with the waveform just below zero for the rest of the time. Different vocal sounds will show different amounts of asymmetry.
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Re: Does this look like LFO DC offset??

Post by dfira »

Right, okay, Also, this may be interesting to you, but I may have told a little porky pie, by omission... that recording is heavily processed, and in the signal chain is an ffmpeg highpass filter (set to 65hz) I always thought their highpass added a significant but hard to describe artifact to the sound, kind of phasey. Well i took it out of the signal path and my waveform is now looks much more symmetrical - well what you would expect
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Re: Does this look like LFO DC offset??

Post by Hugh Robjohns »

dfira wrote: Wed Nov 24, 2021 1:28 pm...in the signal chain is an ffmpeg highpass filter (set to 65hz)

A high-pass filtered signal can't have a dc offset, by definition, since dc is 0Hz and won't get through the filter!!!

always thought their highpass added a significant but hard to describe artifact to the sound, kind of phasey.

The steeper the filter, the greater the phase shift. That can be audible, especially with acoustic instruments.

That phase shift will affect the phase relationship between fundamentals and harmonics, and that will often change the shape of the waveform significantly.
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Hugh Robjohns
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