Sunday, January 29, 2012

+4dBu = Professional/ + 4 times more Signal -10dBV = Consumer /less signal

What is line level? –10dBV and +4dBu mysteries.


I have an Apogee Duet and when I don't do enough recording practice I end up wrangling cables, wires and connections. The duet has a control surface called the Maestro inside the Mac and on the drop downs on the Maestro control ( see picture ) this is a crucial place where I need to select the type of signal going into unit and the particular connector used be it phono/guitar jack or XLR - the three pronged one.

So it could be  XLR  but then does the XLR need phantom power ? and as per the image I can choose XLR with +4dBu or -10dBVso whats that all mean - in terms of the light reading I have done and its not the first time I have tried to grasp it - this is my summary of WTF line level -


Ok Line level is the strength of the signal from or to a piece of audio equipment and the strenth of the signal has consumer ( weak) or Professional ( strong ) strength. The STRONG Rawrr! is 4 times wow four times so that's the plus four out of the way and denotes the need for a higher voltage to carry signals on longer paths in studios etc and the consumer strength is the lesser so that's the minus (-) 


So I think to play with other the signal should match - use the following to remember which is which. Im writing this really for myself so I can refer back to it but you may find it useful also.


PRO + Professional -


CON - Consumer


Mismatch will cause either too-weak signal or distortion. 


So John what about Instrument level - oh brother where art thou? I'll have to research that too but sweetwater has it defined as no set level and usually weak  but depends on the instrument whether it has active element  (battery or added oomph) or passive on the signal or whether is purely electromechanical in nature and so weaker signal.

External Preamp and gain for the duet.
http://www.wikirecording.org/Apogee_Duet_Manual
go in 1/4 - XLR into one of the MIC ports. Then set (in Maestro) the option that says +4dbu or something like that. Then the duet doesn't inpart any gain... it gets the gain from the external preamp


For even more info type this into google and away you go ---
"What is line level? –10dBV and +4dBu demystified"


POSTSCRIPT::

This was included on a previous internal stickie note - its useful so I'll include for our education.



Recording Notes

Line level is a hot output signal  (from a preamp)
Instrument /Mic Level is much lower
http://www.ovnilab.com/articles/linelevel.shtml ( attribution and thanks!)

Instrument-level and mic-level in/outputs are a lot lower than line level
+4 dBu is "professional" line level, common in modern pro recording gear, and it is about 1.25 V.
0 dBv is an average line level, typical output from rackmount guitar/bass preamps.
-10 dBu is "consumer" line level, common with older and cheaper recording gear.
-20 dBu is roughly in the neighborhood of a typical instrument's output.
-30 dBu is again in the neighborhood of a typical microphone's output.

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