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DC OFFSET time for a little education.

Member for

21 years 2 months
Hi,

Could someone explain what DC Offset is? I only have a vague idea of what it is. Been stuck trying to explain what it was to someone who had trouble with it the other day and... well, I couldn't...
I did a search on RO, but did not find anything satisfying enough.


Thank you!

Comments

Member for

16 years 2 months

RemyRAD Thu, 11/02/2006 - 21:41
So you're only now discovering that most everything is bull crap? You're talking about theoretical noise limits in the equipment. Even silicon based stuff has thermal noise. I don't care what kind of microphone preamps you have. I don't care what kind of converters you have, you will never find an environment that will give you much more than a 65 DB signal to noise ratio in real life so all of the specifications are basically moot. Unless you are a moron who is into the ultimate avant-garde and like recording absolutely nothing at all so you can listen to thermal noise? I don't think anybody will talk about how wonderful your production is because it's so quiet? "Oh listen to that nothing, isn't it wonderful?" Right.

If you are a good engineer and know what you're doing, your recordings will sound marvelous regardless of the mindless specifications which really don't mean anything. It's the sound that means something. So you have purchased yourself a nice piece of equipment that will give you nice results, reliable service for years to come, as opposed to a piece of crap equipment that will give you crap results. Be happy with what you have, it's good.

Your comments regarding the "engineer's ears" are ridiculous and unfounded. Those terrible engineers created API. Those terrible engineers created Rupert Neve. That awful equipment isn't worth owning so please send all of that stuff to me.

Now go out and make some nice recordings and stop worrying about stupid numbers, they mean nothing. Making recordings is an art like being a musician. It is neither clinical nor technical albeit technically oriented but for people who want to justify their existence, you can make it as clinical or technical as you desire. It won't make you a better engineer and nobody will care about your signal to noise ratio if you make good recordings.

Wonderful engineer
Ms. Remy Ann David

Member for

17 years 4 months

Groff Fri, 11/03/2006 - 13:17
RemyRAD wrote: So you're only now discovering that most everything is bull crap? ...

If DC offset comes from Behri-Behri converter you will tell that's bad because of crapy and cheap gear. That's ok. When it comes from Apogee .... suddenly things become more relative, tolerant, like nothing really matters at all and the one who reported it could be spec numbers obsessive moronic thermal noise listener with disputable re skills.

:shock:

My recorded waves are decentered, i did the test (the best i can / if it make any sense), found dc offset and reported.

From my experience i have found Rosetta 200 (i suppose it is/should be at least entry level of high end converter league) is not immune of DC offset. So DC offset is not privilege of cheap and crap gear only.

Except the question „do you get what you paid for?“ the one more appropriate for this topic i guess is:

What's the acceptable value/range of DC offset for high end AD?

Member for

16 years 8 months

Zilla Fri, 11/03/2006 - 15:02
Groff wrote: ...I did simple test (I’m not shore if the test is good or scientific, but it's a real life situation) I recorded „silence“, nothing plugged in... The result was the noise around -98 dB...it seems to me… well … higher than I expected.
I suspect you are getting those unexpected readings because of your test set-up. You should not test for noise and offset with your inputs unterminated. That is, you can't just leave the a/d inputs flapping in the breeze, unconnected. You should plug in a low z dummy source load to the inputs. 50-100 ohms should model most device outputs accurately enough.

Member for

17 years 4 months

Groff Fri, 11/03/2006 - 15:46
Thanks Zilla, I didn't try this but I could.

The input bias source resistor in the AD stage could make large noise in measurements so maybe the better way is to shorting all input pins to ground.

Regardless of my testing, recorded waves from mic and inst are somewhat out of the ∞ center line, and that's more problematic than noise floor by itself.

Member for

16 years 8 months

Zilla Fri, 11/03/2006 - 16:19
Either shorting or low z dummy should be good. This will help you indicate the amount of DC offset as it exists in the AD. You have probably already realized that even if the AD is clean, any device connected to it may introduce DC offset as well. Almost all devices have some amount of offset, even really expensive units. It is the degree/quantity of that offset that impacts performance.
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