What do your waveforms look like?

Posted: Fri Jun 13, 2008 6:09 pm

Kev, I am not sure what you mean by "most input sections will have a capacitor couple" - do you mean inputs on preamp or a/d converters or what exactly?

also, at this point DC offset is nothing i know about but Al was saying there looked to be a small DC offset issue with my bass track. i tried using Cubase's remove DC offset but nothing changed.

I run my bass generally just straight out of the bal line out on my GK combo amp and i dont mic the speakers i just unplug them so they dont get into the drum mics..

Posted: Fri Jun 13, 2008 6:28 pm

ok

a transformer couple mic-pre with not carry DC offset through it
the magic of a transformer

DC coupling will
a straight wire is DC coupled

AC coupled is something like the Transformer
or
a capacitor

there is often an AC coupling at the input ... or now I think of it ... the output of an audio section

because I said input I focus on that

If phantom volts is to be applied to a Mic then the Mic-pre gain stage needs to have the DC phanton stripped off
this might be done with a capacitor on each of the differential input legs to the gain stage
pins 2 and 3

that's an obvious DC offset

but music can have the small DC offset issues that Al pointed to
and bass can do this

watch a speaker move out of a bass cabinet ... E130 E 140 JBL often do this
a few reason for this
but lets not look now

this offset probably won't make it through the Mic and Mic-pre combination

here comes the DI
a Transformered DI is cool (AC coupling)
but other DI methods may sneak the DC offset through

even so
" using Cubase's remove DC offset but nothing changed "
this could be that even though there is a high of wave form imbalance there may be an eveness of
area under the graph
and so no DC offset

all why I said not to get too hung up on the offset thing
it's cool to get more knowledge on this as it can be diverse and complicated

otherwise let the equipment do it's job

???
I fear I'm not helping here

Posted: Fri Jun 13, 2008 6:35 pm

its okay - i appreciate the effort on your behalf, Kev Smile

one thing though is that damn wouldnt ya know it, im probably one of the least savvy people i know when it comes to electronics things...anything to do with power/wattage/ohm/resistance/balanced/unbalanced - all this stuff somehow goes right over me no matter how many people have explained things to me...

Posted: Fri Jun 13, 2008 11:10 pm

You will typically see a DC offset when utilizing extremely inexpensive entry-level sound cards. A common problem with Blaster style equipment. This DC offset appears to be above or below the centerline of the display. It is generally a consistent level of offset. Many transform functions in software automatically null it out. For instance when you normalize or modify level, etc.. Some actually have a specific function to remove DC offset from the recording. Unless the offset is really bad, it generally only makes for asymmetrical distortion artifacts which isn't quite the distortion you want. Generally if you're recording sounds awful, it's not the DC offset. If the engineer offset.

Offset put offer
Ms. Remy Ann David

Posted: Sat Jun 14, 2008 10:50 am

Record silence. If it's wildly off then worry. If it's the sound itself, forget about it - it's the singer/instrument.

Our violinist has a violin with a pickup - the sound from that? Alternates to being almost all positive or negative depending on the direction she's bowing. With a spot of reverb it can sound awesome.

Posted: Sat Jun 14, 2008 11:36 am

Easiest way to cure a DC offset: slap a high-pass filter on it. You can set the cutoff as low as 1Hz and it should still work. (Of course a violin could be high-passed much higher than that, and might even benefit from it.)

Posted: Sat Jun 14, 2008 5:46 pm

but that's what the AC coupling is

a simple cap in line is a high pass filter

to pass a signal that can be effected by a 1Hz filter
... well that's getting very close to DC coupled

many digital interfaces wouldn't pass much signal below 10Hz

the violin bow
I say again
look at the area under the graph
it may not be biased as you think

as Remy said asymmetrical distortion artifacts might not be what you want
but asymmetrical waveforms could just be natural for some instruments

the drawn waveforms are not scientific graphs

be aware of DC offset but don't get hung up on it

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