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Laurier Tiernan

Joined: 25/10/11
Posts: 2
Loc: Tokyo, Japan

dbv/dbu?
#949175 - 25/10/11 12:14 PM

Hi Folks,

My name is Laurier Tiernan and I am a Canadian musician living in Tokyo. I was certified as a sound engineer some 10 years go, but I haven't worked much as a studio engineer since then, and I'm just getting back into it.

This is leading me to all kinds of technical questions on which my brain is foggy.

One in particular is about the relationship between dbv and dbu.

For example, what is the mathematical distance between -10dbv and +4dbu?

If anyone could help me with this, I would be very grateful.

Thank you for taking the time to read this post.

May you all have a great week.

All Good Things to You,

Laurier Tiernan

--------------------
http://www.facebook.com/natureairliner http://www.facebook.com/LaurierTiernanMusic

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BJG145

Joined: 06/08/05
Posts: 2155
Loc: Norwich UK

Re: dbv/dbu? new

[Re: Laurier Tiernan]
#949182 - 25/10/11 12:39 PM

Hi Laurier -

There's a SOS article explaining the differences here:

http://www.soundonsound.com/sos/1994_articles/feb94/decibels.html

Note that dBv and dBu are the same, though dBV is something else...

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Tomás Mulcahy
active member

Joined: 25/04/01
Posts: 2815
Loc: Cork, Ireland.

Re: dbv/dbu? new

[Re: Laurier Tiernan]
#949198 - 25/10/11 01:16 PM

Forget about forums for this kind of info, you will learn it much faster, and also learn a lot of other interesting and useful things, with this classic book:
http://www.amazon.com/Sound-Reinforcement-Handbook-Gary-Davis/dp/088188900 8

--------------------
madtheory creations
Synths and pianos for Kontakt

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Hugh Robjohns
SOS Technical Editor

Joined: 25/07/03
Posts: 18355
Loc: Worcestershire

Re: dbv/dbu? new

[Re: Laurier Tiernan]
#949259 - 25/10/11 04:13 PM

Quote Laurier Tiernan:

For example, what is the mathematical distance between -10dbv and +4dbu?

Not quite sure what you mean by 'mathmatical distance'. In terms of signal voltage the difference is just under 12dB, with +4dBu being almost 12dB louder than -10dBV.

When discussing such things it really is important to pay meticulous attention to using the correct terms -- there are significant differencen between the meaning of capital and lower case letters in some situations here, and getting it wrong just adds to the potential confusion.

The professional audio level reference, 0dBu, is derived from an alternatice standard using 0dBm and is essentially the same voltage reference but without any specific impedance requirements (the 'u' in dBu refers to 'unterminated'). The electrical signal reference level of 0dBu is 0.775V rms.

This was also the voltage produced across a 600 ohm load when 1mw of power was consumed within it -- a measure of signal power used in the telecom industry and elsewhere, and denoted by 0dBm -- the 'm' referring to milliwatt). In olden days audio equipment also employed matched 600 ohm terminations, but this approach has long since been obsolete, and hence we have discarded the use of dBm in favour of dBu.

In European broadcasting circles the standard audio level reference is 0dBu (0.775V rms), but a lot of pro-audio equipment has adopted a higher standard operating level which evolved from American broadcast practices. This level is +4dBu.

Using the equation dB = 20log(V1/V2), where V1 is an unknown voltage and V2 is the reference,

+4dBu = 1.2283V rms

The semi-professional audio level reference, 0dBV, is derived from a reference voltage of 1.0Volt rms. The electrical signal reference level employed with semi-pro equipment is 10dB lower than 1 volt rms, hence -10dBV and a voltage of 0.316V rms.

Using the same forumula, but with these two signal voltages (+4dBu and -10dBV) we have:

db = 20log(1.2283/0.316) = 11.79dB

This is the level difference between the standard reference levels of +4dBu and -10dBV.

Hope that helps.

hugh

--------------------
Technical Editor, Sound On Sound

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Laurier Tiernan

Joined: 25/10/11
Posts: 2
Loc: Tokyo, Japan

Re: dbv/dbu? new

[Re: Laurier Tiernan]
#958039 - 09/12/11 02:06 AM

Thank you very much to everyone who replied. I really appreciate your help.

May you have a great weekend.

--------------------
http://www.facebook.com/natureairliner http://www.facebook.com/LaurierTiernanMusic

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dmills

Joined: 25/08/06
Posts: 2129

Re: dbv/dbu? new

[Re: Laurier Tiernan]
#958041 - 09/12/11 02:23 AM

Just to confuse things 0dBu also has an alternative (and much earlier) meaning, being dB referred to 1 microwatt, very common in radio engineering to this day, so you need to watch the context on this one.

Regards, Dan.

--------------------
Audiophiles use phono leads because they are unbalanced people!

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