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J-MADD 7 February 2006

Hi all,

I am planning on sending a couple Wav. files off to be professionally mastered. Should I remove the DC offset with Sound Forge prior to it going to the ME? Thanks all.

Justin

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J-MADD Thu, 02/09/2006 - 08:19

I was just wondering because I always have soundforge atomatically remove DC off set prior to Normalizing, eqing etc... Will a mastering engineer check just in case anyways? Like I say I may not really have an issue with DC offset, but I am told if it is there, the maximum headroom of a mix will be less. Thanks for the replies.

Justin

Reggie Fri, 02/10/2006 - 11:12

Massive Mastering wrote:
"Lopsided" waveforms aren't all that unusual and it's often confused (especially in this "volume-crazed" society) as DC offset.

I had this happen fairly recently. My right overhead waveform had much longer "legs" on the negative side than on the positive side. It turned out sounding OK, but I never figured out exactly what caused it. Is it simply caused by mic positioning, or could it be an electrical thing, or what?

Massive Mastering Fri, 02/10/2006 - 23:52

It can happen a lot with certain percussive instruments, it's very common on brass... Some vocalists - Especially the more "raspy" types. It can also be phase issues, could be compression settings... Not everything makes a perfectly balanced sine wave.

But as long as it sounds right, who cares...

It's one of those things that's always been aorund, but nobody thought about - before you could *see* it... :lol:

RemyRAD Sat, 02/11/2006 - 12:30

You know folks, natural audio in real life is asymmetrical, not symmetrical. Symmetrical waveforms are only produced by electronic test equipment.

The issue of larger negative legs versus positive going legs within our software displays is a bit of a mystery to me also? In broadcast AM radio, the FCC allows for 125% positive going modulation but only 100% negative going modulation. We try to avoid DC offsets which actually can re-create more positive versus negative apparent modulation and vice versa but that moves the baseband as opposed to negative versus positive at the same 0 baseband. The FCC had previously allowed up to 200% positive going modulation! How this relates to recording, I'm not certain? I'm not clear on whether, within our different software's whether the waveform has been "printed" properly for our viewing??

Is recorded modulation actually more heavily negative than positive in general in real life?? I have not been able to test my respective system and software to find out whether the indicated waveform display is correct? I believe I would need a positive pulsed frequency sweep generator to test this hypothesis (sorry I don't have one)? I discovered such a problem 25 years ago when working for Scully as their quality control manager and final test technician. Our test tapes coming from MRL utilized a pulsed frequencies sweep, whose response was indicated on a oscilloscope gradicule. One day, our worn-out test tapes started yielding better frequency response on our 280B recorders then our new test tapes!?!? I narrowed this down to a change in procedure from M. R. L. and the way they manufactured our pulsed frequency sweep test tapes. When I called them about this, they said I was nuts! I went home scratching my head. The next day, I received a call where they apologized to me and realized that they had inadvertently changed the pulse from a positive going pulse to a negative going pulse which affected frequency response in the first stage playback preamp! I was correct! They replaced all of our test tapes with positive going pulses, before the sweep. I believe this proves that absolute polarity within recorded sound does have a factor on the final quality. I discovered that the first stage preamplifiers capacitors in the 280, were being charged differently by the trigger pulse.

Of course the way recorded sound is affected is all subjective. I have inverted phase and reversed polarity on my monitor system in the past to try and subjectively realize this difference. I have found that absolute polarity and inverted phase does provide a difference in the monitoring experience. To what extent everybody else believes my findings, I'm not sure? The jury is still out.

I love the old Scully but where is Fox??
Remy X David

anonymous Thu, 02/16/2006 - 04:36

Yep this phenomoenon has baffled me too in the past ,though I'm quite new to mastering.I find its usually percussive instruments which show a wave form such as this too.I've never had any sound quality issues though it looks as though there should have been,I'm interested too.I put it down to a display issue as well but it seems there is more too it.As John said it really has only been noticed by the majority since digital editing has become common place.

DeeDrive Mon, 02/20/2006 - 08:12

Most Mastering Engineer's I've dealt with will put a high pass filter at around 25-30hz over everything they master, which eliminates DC offset, so it shouldn't be a problem. DC is just AC with a frequency of 0. It wouldn't hurt to do it yourself though. And for god's sake, everyone stop normalizing, it's useless.

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