The importance of DC correction

[Dysphuncktional]

Hey peeps, dunno if this is up already but I though I'd share my knowledge on this.
I use buzz for all of my production and an issue i have with this is some of the machines (inckluding VSTis) generate a signal with a slight dc offset. Another area where dc offset occurs alot is samples. This is bad. Why? Well, for one thing, a high amount of dc offset on a given signal can result in nasty clicks. Another thing DC offset screws with is your dynamics range. What is DC offset? well, its like a phase shift on a sample, except its vertical rather than horizantal. Every sample editor you've ever seen probably had a line running smack dab in the middle of the sample. Now picture an imaginary line also going smack dab in the vertical center of the wave, this line should line up exactly with the line in the wave editor as a crude example, if its above or below this line the center of the sample is above or below this line and this is dc offset. This is also a very useful example for how to chop up samples, the first sample in the wave should ALWAYS start in this middle line, and the same goes for the last sample in the wave. Think of the wave continueing on where it ends, starting from the beginning again. If this lines up you will never have a click at the end or beginning of your sample. As for the dynamics range, the wave is not ligned up vertically, which means you will have for that given signal more signal and volume at either the postive or negative side (top or bottom). This by itself alone, is rather nasty sounding, you probably wont hear it at first but if the dc offset is big and you correct it you will definitely hear a difference in crispness. it also means that the other signals have to compete more with the dc offsetted signal on either the top or the bottom half, and less on the other half. Now in buzz i have a nice little fixer machine which i can hook up directly after any 'bad' signal and it fixes dc problems in real time. I dunno how you would go about doing this in FL or reason thats up to you to figure out, but for samples almost all sample editors have a dc correction function, find it, learn it, use it. hope this wasnt too confusing and it helps anyone.
peace

 

[WingsOfAnAngel]

Dc Offset

good post! here are my 31.5 cents:

"In a studio or mastering environment, nothing is more important than maintaining the utmost audio quality throughout the mix. One of the common problems that is encountered, that effects this is referred to as 'DC Offset', and simply means that a given audio source does not have the correct 0-crossing, and is shifted either up or down from there."

"What is DC OFFSET?
16bit sound sample data contains values between -32768 and +32767. When you
sample a sound, the values have optimally mid point at zero, so when you look
at the graph of the sample with a sound editor, you should see a nice
waveform which is centered at the middle of the graph.
When a sample has DC offset, it is not centered at the middle, but it is
either below or over the center axis. Sound data is usually distributed
equally below and over the center axis so when you have DC offset,
the dynamical range of the sound is limitted which means that the sound can't
be as loud as it could be. A large DC offset also causes snaps when the sample
ends, because the signal drops fast from the offset level to the real zero
level. To make it more simple: You can force a sample to have dc offset by adding
some number to all the samples. Like if you add +10 to all the samples the
dc offset will be +10."

"What is DC offset, and why don't we like it?
DC offset is a significant problem because it can dramatically reduce the dynamic range (the range between the loudest & quietest sound) of a recording.
Essentially, DC offset means that what should be digital silence (a value of 0) is not actually equal to 0 (Rather paradoxically, the DC offset is a signal with a frequency of 0, this is why a highpass filter removes the problem). If the recording has a DC offset, the positive peaks of the waveforms are higher than they should be, and you may encounter sample clipping when you amplify the sound in any way, which may not have occured if you had corrected the offset. A significant amount of samples one finds on the net have a DC offset.
To remove DC offset within buzz, I suggest you pass your entire mix down through Cyanphase's 'Auto DC Blocker' or Automaton's 'DC Eliminator'. Do this _before_ any compression or EQ'ing. DC offset can also be seen using Harc's 'Vision' machine after any generators which you are suspicious of. Samples are best processed beforehand, using your favourite Sample editor's 'FFT filter' feature so as not to compound error"

All The Best,
Wings

 

[Kevin A]

Great Post Guys.
In FLstudio, in the sampler channel, there is a button to turn the DC offset on or off.

 

[Formant024]

Ook hallo lol!

 

[UnOwn]

I should have asked this the first time I read it but I was just wondering, why don't programs just automatically remove DC Offset if it is bad (which I believe you guys about)? What causes it to be there in the first place, why don't they just line up when recording? Is there any reason at all that someone would want it there (basically, why would programs not automatically remove it)? Just curious.

 

[RigorMortis]

so far i only encountered it once, ofcourse i took the appropiate measures to deny its existence.

 

[UnOwn]

so far i only encountered it once, ofcourse i took the appropiate measures to deny its existence.

WTF Are you talking about???? LOL

 

[Dysphuncktional]

Well, Im not sure about all of that, I just know that in my case it's due to several buggy coded buzz machines which produce output with dc offset. There are also numerous VST plugins and Im sure other types of homebrewed programs/plugins also suffer from output
with dc offset. It may be because the dev is unaware, or is not concerned with or considering it so it doesnt get caught. In the case of samples, if you have samples that come from older tunes, chances are there is dc offset on this too, it depends. In any case, any decent sample editor detects and fixes this for you. Rule of thumb, when ripping a sample from cd/mp3/vynil/mic whatever, check and fix dc first thing so you wont have to worry about it anymore.

As far as your question of how it may be useful, well, consider for example a click-and-pop generator (produces clicks-and-pops akin to what's heard on vynil records). The output of this will not even be a wave at all. it will most likely be a long stream of 0 db (dc level) with the occasional one or several samples abruptly spiking, this is audible to you as clicks and pops