mV vs. dBu vs. dBv?
Chris Rupert
On audio equipment, I frequently see input or output levels given in units
of dBu, e.g. an input level of -20dBu or +4 dBu. What does dBu stand for?
How does this relate to millivolts? I know that a line level can be
anywhere from about 500mV - 2V. Is there a conversion method to go from dBu
to mV like there is from gain to dB, or are mV and dBu incompatible? Also,
on scopes, I've seen the magnitude measured in dBv. What does that mean,
and how does it relate to gain or voltage?
Thanks
Chris Rupert
cru...@netrover.com
http://www.netrover.com/~crupert
Mark McQuilken
Chris,
It's:
+4dBm (1mW level; 1.228Vrms)
-20dBu (0 dBu = 0.775Vrms)
-10dBV (0 dBV = 1Vrms)
0dBv = 0 dBu
x dBu = 20 * log (Vin/0.775V)
x dBV = 20 * log (Vin/1)
x dBm = 20 * log (Vin/0.775V)
Vin(dBu) = 0.775V * 10**(x dBu/20) etc.
Whether they're compatible (or not) is a question for "Change of
Heart"...:>)
6dB down in Austin,
McQ
--
Mark McQuilken
FMR Audio
http://www.fmraudio.com
(800) 343-9976
(512) 280-6557
Mark Plancke
>Hi;
>
>On audio equipment, I frequently see input or output levels given in units
>of dBu, e.g. an input level of -20dBu or +4 dBu. What does dBu stand for?
>How does this relate to millivolts? I know that a line level can be
>anywhere from about 500mV - 2V. Is there a conversion method to go from dBu
>to mV like there is from gain to dB, or are mV and dBu incompatible? Also,
>on scopes, I've seen the magnitude measured in dBv. What does that mean,
>and how does it relate to gain or voltage?
>
This is covered in the F.A.Q.
Mark Plancke
SOUNDTECH RECORDING STUDIOS
Windsor, Ontario, Canada
http://SoundTechRecording.com
mailto:Ma...@SoundTechRecording.com
Anahata
cru...@netrover.com "Chris Rupert" writes:
> What does dBu stand for?
> How does this relate to millivolts?
In practice dBu and dBv are the same and are 20 x log (base 10) of
the ratio of the voltage to a standard voltage. That standard voltage,
for reasons buried in the history of telephony, is that which produces
1 mW in a 600 ohm load. This works out at 0.775 volt rms, which is
therefore the 0dBu standard. Hence +20dBu = 7.75Vrms, and -20dBu =
77.5mV, and with a calculator you can work out other values.
--
Anahata
ana...@freereed.demon.co.uk http://www.freereed.demon.co.uk/
ana...@locust.co.uk (1st 8 lines sent as text message to mobile phone)
phone 0171 229 6076 home, 0171 638 5577 work, 0976 263827 Orange mobile
Mike Rivers
In article <01be3820$313023e0$341fd1cd@default> cru...@netrover.com writes:
> On audio equipment, I frequently see input or output levels given in units
> of dBu, e.g. an input level of -20dBu or +4 dBu. What does dBu stand for?
Decibels, relative to the voltage that it takes to pump 1 milliwatt into
a 600 ohm load, about 0.775 volts (Ohm's Law will confirm that). But
it's a voltage measurement, not a power measurement, so dBu is measured
across a high impedance (low power) load.
> Is there a conversion method to go from dBu
> to mV like there is from gain to dB
Yes, it's exactly the same formula only the reference voltage for the
gain is known so you work it in the other direction.
> Also,
> on scopes, I've seen the magnitude measured in dBv. What does that mean,
> and how does it relate to gain or voltage?
I haven't seen a scope calibrated in dBv, but I suppose there could be
one. You have to be careful about this one. In the US, we have dBV
(upper case V) which is dB relative to 1 volt rather than 0.775 volts.
This makes arithmetic easier, and it's usually used for the "semi pro
studio" equipment with a nominal operating level of -10 dBV. But over
in Europe, the use (or at least at one time used, but I think they've
pretty much become Americanized) dBv (lower case v) to mean the same
thing as our dBu - dB relative to the 1mW/600ohm voltage, but with the v
signifying that it's a voltage measurement rather than a power
measurement.
There's also dBm, which is a power measurement. In audio, it's dB
relative to 1 milliwatt, usually measured into a 600 ohm load unless
otherwise specified. In RF, it's usually measured into a 50 or 75 ohm
load.
Confused yet?
--
Mike Rivers (I'm really mri...@d-and-d.com)
budgie
wrote:
>In article <01be3820$313023e0$341fd1cd@default>
> cru...@netrover.com "Chris Rupert" writes:
>
>> What does dBu stand for?
>> How does this relate to millivolts?
>
>In practice dBu and dBv are the same and are 20 x log (base 10) of
>the ratio of the voltage to a standard voltage. That standard voltage,
>for reasons buried in the history of telephony, is that which produces
>1 mW in a 600 ohm load. This works out at 0.775 volt rms, which is
>therefore the 0dBu standard. Hence +20dBu = 7.75Vrms, and -20dBu =
>77.5mV, and with a calculator you can work out other values.
Right angle, wrong result
dBm is dB relative to 1 milliwatt, a POWER level which canot be
defined in terms of voltage unless impedance is known. As pointed
out, in 600ohm it is0.775Vrms.
dBv is decibels relative to a VOLT. Often RF millivolt meters are
calibrated in mV and dBv.
dBu is dB relative to a microvolt.
Peter
Remove the NOWHERE from reply address
Anahata
bud...@NOWHERE.cantech.net.au "budgie" writes:
> On Mon, 04 Jan 99 21:50:12 GMT, Ana...@freereed.demon.co.uk (Anahata)
> wrote:
>
> >
> >In practice dBu and dBv are the same and are 20 x log (base 10) of
> >the ratio of the voltage to a standard voltage. That standard voltage,
> >for reasons buried in the history of telephony, is that which produces
> >1 mW in a 600 ohm load. This works out at 0.775 volt rms, which is
> >therefore the 0dBu standard. Hence +20dBu = 7.75Vrms, and -20dBu =
> >77.5mV, and with a calculator you can work out other values.
>
> Right angle, wrong result
>
> dBm is dB relative to 1 milliwatt, a POWER level which canot be
> defined in terms of voltage unless impedance is known. As pointed
> out, in 600ohm it is0.775Vrms.
I did say 'in practice', by which I meant that practice is to take that
voltage and call it 0dBu, and then describe voltages as if the
impedance were always 600 ohms, even though it isn't.
> dBv is decibels relative to a VOLT. Often RF millivolt meters are
> calibrated in mV and dBv.
My understanding was the 1 volt reference (which I deliberately didn't
mention to avoid confusion) was designated dBV (note capital V),
and that was an American standard that had given way to the European
dBu or dBv (ref 0.775V)
> dBu is dB relative to a microvolt.
I don't remember it meaning that when I worked for Neve in 1980. Is my
memory that bad?
Mark McQuilken
>
(snip happens)
>
> > dBv is decibels relative to a VOLT. Often RF millivolt meters are
> > calibrated in mV and dBv.
>
> My understanding was the 1 volt reference (which I deliberately didn't
> mention to avoid confusion) was designated dBV (note capital V),
> and that was an American standard that had given way to the European
> dBu or dBv (ref 0.775V)
>
> > dBu is dB relative to a microvolt.
>
> I don't remember it meaning that when I worked for Neve in 1980. Is my
> memory that bad?
>
> --
> Anahata
Anahata:
No, you are correct. dBu = dBv (re: 0.775Vrms) as you said. dBV is
relative to 1V as you say...
All-knowing and always kerrect...er...correct in Austin,
budgie
wrote:
>Anahata wrote:
>>
>(snip happens)
>>
>> > dBv is decibels relative to a VOLT. Often RF millivolt meters are
>> > calibrated in mV and dBv.
>>
>> My understanding was the 1 volt reference (which I deliberately didn't
>> mention to avoid confusion) was designated dBV (note capital V),
>> and that was an American standard that had given way to the European
>> dBu or dBv (ref 0.775V)
>>
>> > dBu is dB relative to a microvolt.
>>
>> I don't remember it meaning that when I worked for Neve in 1980. Is my
>> memory that bad?
>>
>> --
>> Anahata
>
>Anahata:
>
>No, you are correct. dBu = dBv (re: 0.775Vrms) as you said. dBV is
>relative to 1V as you say...
>
>All-knowing and always kerrect...er...correct in Austin,
>McQ
Then if that's correct in Austin the US practice is at variance with
the real world.
[don asbestos suit - flame war about to start]
Mark McQuilken
>
> Then if that's correct in Austin the US practice is at variance with
> the real world.
>
> [don asbestos suit - flame war about to start]
>
> Peter
But, Peter, this ISN'T the real world...this is AUDIO! :>)
As long as I've been doing audio, that's the way it's been. I've heard
various stories about how the different forms have been developed and
equated, but it's all hearsay. But suffice it to say that we're all
pretty-much uniformly confused if, relative to the rest of the world,
we're practicing some bastard form of science. Although hardly a seminal
work (or even a defacto standard), check Audio Precision's documentation
(particularly Audio Measurement Handbook; also their test sets) for the
above-given definitions. At least one of the world's leading audio
instrumention companies is also confused along with us...
Uniformly and consistently confused in Austin (and elsewhere too),
Peter Smerdon
>
>> dBu is dB relative to a microvolt.
>
>I don't remember it meaning that when I worked for Neve in 1980. Is my
>memory that bad?
>
>--
The use of dBu depends on the context.
RF practitioners use dBu as dB wrt a 1 microvolt reference in field
strength measurements. The "u" should be the Greek character "mu"
making it dBµ - but that's not so easy to do on a keyboard (usually
possible, but not easy for most folks with a US/English keyboard
driver).
There was some discussion in the broadcast field (where audio and RF
meet) when the dBm made way for the dBu about the confusion - but I
don't recall any resolution.
Consider an FM station - RF field strength of 60 dBµ and a transmitter
with an audio input sensitivity of 10dBu
Myself, I just note the context - just like the word "minute" (are we
talking "object - very small" or "time - sixty seconds")
PS - I hope my attempt at the "mu" character worked on your newsreader
if not then the character µ = "mu"
,-._|\ Peter Smerdon Technical Manager (Melbourne)
/ Oz \ SBS Radio Australia's multicultural broadcaster
\_,--.x/ Email: smer...@melbpc.org.au, peter....@sbs.com.au
v For info on SBS Radio and TV see - http://www.sbs.com.au
Mike Rivers
> But suffice it to say that we're all
> pretty-much uniformly confused if, relative to the rest of the world,
> we're practicing some bastard form of science.
Nothing confusing about it. dB is ratio, period. dBu is volts relative
to 0.775 (why that number was chosen is, for the sake of this argument,
irrelevant), and dBV is volts relative to a perfectly reasonable number
of volts, 1. dBm is never volts. dBv is European and they never do
anything right over there anyway.
- MR, the All American Boy
Mark McQuilken
I was trying to be nice, Mike...but, what the HEY!! Bastard
micro-volts...BAH! Eat our dBus/dBVs/dBms, etc.!!!
- McQ, another All American Boy (in Austin...y'all)