[Randy Yates]

Dear Audio Professionals,

Questions on levels:

1. If you backtrack to 0 dB from this wikipedia article

http://en.wikipedia.org/wiki/Line_level

the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

2. Is there a standard for converting from dBFS to dBu? If so,
what is it?

3. If the answer to 2 is yes, then does that standard use FS sine
or FS square?

Thanks for any insights.
--
Randy Yates % "Maybe one day I'll feel her cold embrace,
Digital Signal Labs % and kiss her interface,
% til then, I'll leave her alone."
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Randy Yates]

cross-posting to rec.audio.pro

--RY

Randy Yates writes:

Dear Audio Professionals,

Questions on levels:

1. If you backtrack to 0 dB from this wikipedia article

http://en.wikipedia.org/wiki/Line_level

the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

2. Is there a standard for converting from dBFS to dBu? If so,
what is it?

3. If the answer to 2 is yes, then does that standard use FS sine
or FS square?

Thanks for any insights.

--
Randy Yates % "And all that I can do
Digital Signal Labs % is say I'm sorry,
% that's the way it goes..."
http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO

[Randy Yates]

One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

--RY


Randy Yates writes:

cross-posting to rec.audio.pro

--RY

Randy Yates writes:

Dear Audio Professionals,

Questions on levels:

1. If you backtrack to 0 dB from this wikipedia article

http://en.wikipedia.org/wiki/Line_level

the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

2. Is there a standard for converting from dBFS to dBu? If so,
what is it?

3. If the answer to 2 is yes, then does that standard use FS sine
or FS square?

Thanks for any insights.

--
Randy Yates % "With time with what you've learned,
Digital Signal Labs % they'll kiss the ground you walk
% upon."
http://www.digitalsignallabs.com % '21st Century Man', *Time*, ELO

[dizzy]

Randy Yates wrote:

One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

Most preamps will put out close to 10 VRMS, considering the typical
+/- 15V power-supply rails...

[PStamler]

Randy Yates wrote:
One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No. I've seen some that clip at +30dBu.

Peace,
Paul

[Arny Krueger]

"dizzy" wrote in message

Randy Yates wrote:

One other question: is there a specification on the
absolute maximum signal voltage magnitude for a line
level output?

Most preamps will put out close to 10 VRMS, considering
the typical +/- 15V power-supply rails...

One word: tubes.

[PStamler]

On Nov 19, 7:41*am, "Arny Krueger" wrote:
"dizzy" wrote in message



Randy Yates wrote:

One other question: is there a specification on the
absolute maximum signal voltage magnitude for a line
level output?

Most preamps will put out close to 10 VRMS, considering
the typical +/- 15V power-supply rails...

One word: tubes.

And two more words: differential outputs.

With higher supply voltages (like +/- 21V) there are several common
opamps which will (just) put out +24dBu. Use a pair of them as a
differential output and you get +30dBu max output. Or you can use a
higher-supply-voltage discrete circuit or, as Arny says, tubes.

Peace,
Paul

[Scott Dorsey]

In article , Randy Yates wrote:
One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No, and that's the problem. The standards are average and not peak standards,
and so the amount of headroom required over average is not defined.

For me, I'd like to see 20 dB over average level before clipping, maybe more.
Unfortunately a lot of "pro audio" gear does not do this.

I believe your questions are answered by IEC 60027-3, and by AES standard
AES-R2-1998. Peak-reading standards are in AES-R7-2006.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Klay_Anderson]

On Nov 19, 8:29*am, (Scott Dorsey) wrote:
In article , Randy Yates wrote:

One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No, and that's the problem. *The standards are average and not peak standards,
and so the amount of headroom required over average is not defined. *

For me, I'd like to see 20 dB over average level before clipping, maybe more.
Unfortunately a lot of "pro audio" gear does not do this.

I believe your questions are answered by IEC 60027-3, and by AES standard
AES-R2-1998. *Peak-reading standards are in AES-R7-2006.
--scott


The nice thing about standards is that there are so many of them.

I have posted a JPEG scan of a level scales card I picked up some time
ago a convention. It shows the relationship of 0.775Vrms to most
known standard scales.

See: http://www.klay.com/klay/world_audio_levels.jpg

Text "Klay" to 50500 for contact info

-.- .-.. .- -.-- / .- - / -.- .-.. .- -.-- / -.. --- - / -.-. --- --
Yours truly,

Mr. Klay Anderson, D.A.,Q.B.E.

[Randy Yates]

(Scott Dorsey) writes:

In article , Randy Yates wrote:
One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No, and that's the problem. The standards are average and not peak standards,
and so the amount of headroom required over average is not defined.

For me, I'd like to see 20 dB over average level before clipping, maybe more.
Unfortunately a lot of "pro audio" gear does not do this.

I believe your questions are answered by IEC 60027-3, and by AES standard
AES-R2-1998. Peak-reading standards are in AES-R7-2006.
--scott

Excellent information - thanks Scott!
--
Randy Yates % "With time with what you've learned,
Digital Signal Labs % they'll kiss the ground you walk
% upon."
http://www.digitalsignallabs.com % '21st Century Man', *Time*, ELO

[PStamler]

On Nov 18, 8:39*pm, Randy Yates wrote:
* 1. If you backtrack to 0 dB from this wikipedia article
* *http://en.wikipedia.org/wiki/Line_level
* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
* respectively. Is this correct? Are the reference levels I've given
* here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --
that's the voltage equivalent of 1mW into a 600 ohm load. The
reference level for dBV is exactly 1V.

* 2. Is there a standard for converting from dBFS to dBu? If so, * what is it?

No. There's an informal standard used in the film industry and in many
broadcast applications of +4dBu = -20dBFS, but it's never been
codified as an official standard. The informal standard, though, is (I
believe) based on an rms scale -- in other words, a tone that would
read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct
me if I'm wrong on that last bit, but that's what I think is the case.

Peace,
Paul

[Adrian Tuddenham[_2_]]

PStamler wrote:

On Nov 18, 8:39*pm, Randy Yates wrote:
* 1. If you backtrack to 0 dB from this wikipedia article
* *http://en.wikipedia.org/wiki/Line_level
* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
* respectively. Is this correct? Are the reference levels I've given
* here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --
that's the voltage equivalent of 1mW into a 600 ohm load. The
reference level for dBV is exactly 1V.

* 2. Is there a standard for converting from dBFS to dBu? If so, *
what is it?

No. There's an informal standard used in the film industry and in many
broadcast applications of +4dBu = -20dBFS, but it's never been
codified as an official standard. The informal standard, though, is (I
believe) based on an rms scale -- in other words, a tone that would
read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct
me if I'm wrong on that last bit, but that's what I think is the case.

The optimum reference headroom (the difference between reference level
and full-scale level) would vary according to the application and the
equipment used. With lots of bits to spare, 20dB would be fine, but if
you were recording to 16-bit CD standards, you would have thrown away
20dB of your potential dynamic range and dropped your signal/noise ratio
to around 45 dB for average levels. (Digital noise sounds horrible, much
worse than analogue noise, so you really do want to keep clear of it.)

For something like A.M. broadcasting, a reference headroom of around 12
dB is more common and that is also quite satisfactory for 16-bit
recordings provided you are prepared to control the gain intelligently
on the very loudest passages. If part of the chain is in mono, there is
the further complication that two stereo channels can add to give any
level from much lower to 6dB higher, depending on coherence and phase.

For professional use, the system of marking the beginning of a recording
with a burst of reference tone (or a series of squeaks if equalisation
is involved) is the simplest way of ensuring the correct playback or
copying level.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Randy Yates]

Hi Paul,

Thank you for your answers. Comments below.

PStamler writes:

On Nov 18, 8:39Â*pm, Randy Yates wrote:
Â* 1. If you backtrack to 0 dB from this wikipedia article
Â* Â*http://en.wikipedia.org/wiki/Line_level
Â* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
Â* respectively. Is this correct? Are the reference levels I've given
Â* here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --
that's the voltage equivalent of 1mW into a 600 ohm load.

Ah, that's right - it's the voltage level that corresponds to 0 dBm (1
mW) when delivering to a 600 ohm load.

The reference level for dBV is exactly 1V.

Got it.

Â* 2. Is there a standard for converting from dBFS to dBu? If so, Â* what is it?

No. There's an informal standard used in the film industry and in many
broadcast applications of +4dBu = -20dBFS, but it's never been
codified as an official standard. The informal standard, though, is (I
believe) based on an rms scale -- in other words, a tone that would
read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct
me if I'm wrong on that last bit, but that's what I think is the case.

There seems to be no universal agreement, but you are close to what this
guy says (under "Here come the numbers..."):

+22dBu = 0dBFS == +4dBu = -18dBFS.

I'm still not sure if that's FS sine or FS square.
--
Randy Yates % "Remember the good old 1980's, when
Digital Signal Labs % things were so uncomplicated?"
% 'Ticket To The Moon'
http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra

[Mike Rivers]

On 11/19/2010 10:01 AM, Randy Yates wrote:

+22dBu = 0dBFS == +4dBu = -18dBFS.
I'm still not sure if that's FS sine or FS square.

dBFS is a peak level. But since good peak reading meters
(and good average reading meters as well) are pretty rare,
generally we look at the RMS value of a sine wave when
expressing levels.

I determine the maximum input level experimentally by
feeding in a sine wave, watching the digital meter, and
looking at the RMS value of the sine wave when the overload
light just comes on. To be more accurate, I'll record a bit
and examine the level for clipping, boosting the input level
incrementally until I'm sure I'm reaching full scale on peaks.

For outputs, I'll use a program to generate a 0 dBFS sine
wave, play it, and read the RMS level of the output.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Randy Yates]

Mike Rivers writes:

On 11/19/2010 10:01 AM, Randy Yates wrote:

+22dBu = 0dBFS == +4dBu = -18dBFS.
I'm still not sure if that's FS sine or FS square.

dBFS is a peak level.

That's not the way I understand it. Am I wrong? It's
no different than dBu or dBV - just a different "reference"
level. Thus it would be an RMS measure.

But since good peak reading meters (and good average reading meters as
well) are pretty rare, generally we look at the RMS value of a sine
wave when expressing levels.

So you're saying then it's FS sine.
--
Randy Yates % "Maybe one day I'll feel her cold embrace,
Digital Signal Labs % and kiss her interface,
% til then, I'll leave her alone."
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Scott Dorsey]

In article , Randy Yates wrote:
No. There's an informal standard used in the film industry and in many
broadcast applications of +4dBu = -20dBFS, but it's never been
codified as an official standard. The informal standard, though, is (I
believe) based on an rms scale -- in other words, a tone that would
read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct
me if I'm wrong on that last bit, but that's what I think is the case.

There seems to be no universal agreement, but you are close to what this
guy says (under "Here come the numbers..."):

+22dBu = 0dBFS == +4dBu = -18dBFS.

I'm still not sure if that's FS sine or FS square.

That's assuming a sine wave.

Unfortunately if you use that standard and you record a trumpet with peaks
at 0 dBu, you'll clip the hell out of your converters.

This is because trumpets aren't making sine waves.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[David Nebenzahl]

On 11/19/2010 7:45 AM Scott Dorsey spake thus:

In article , Randy Yates
wrote:

No. There's an informal standard used in the film industry and in
many broadcast applications of +4dBu = -20dBFS, but it's never
been codified as an official standard. The informal standard,
though, is (I believe) based on an rms scale -- in other words, a
tone that would read 0 VU on a VU meter calibrated to +4dBu would
be -20dBFS. Correct me if I'm wrong on that last bit, but that's
what I think is the case.

There seems to be no universal agreement, but you are close to what
this guy says (under "Here come the numbers..."):

+22dBu = 0dBFS == +4dBu = -18dBFS.

I'm still not sure if that's FS sine or FS square.

That's assuming a sine wave.

Unfortunately if you use that standard and you record a trumpet with peaks
at 0 dBu, you'll clip the hell out of your converters.

This is because trumpets aren't making sine waves.

Nor violins. (Make pretty close to a triangular wave, I believe.)


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

[Bill Graham]

"Randy Yates" wrote in message
...
Hi Paul,

Thank you for your answers. Comments below.

PStamler writes:

On Nov 18, 8:39 pm, Randy Yates wrote:
1. If you backtrack to 0 dB from this wikipedia article
http://en.wikipedia.org/wiki/Line_level
the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --

Wow! You have a calculator that goes to 32 significant digits? My old HP15C
is only good for about 15. You can calculate the distance to Alpha Centauri
to the nearest tenth of an inch...:^)

[PStamler]

On Nov 19, 7:18*pm, "Bill Graham" wrote:
"Randy Yates" wrote in message

...

Hi Paul,

Thank you for your answers. Comments below.

PStamler writes:

On Nov 18, 8:39 pm, Randy Yates wrote:
1. If you backtrack to 0 dB from this wikipedia article
http://en.wikipedia.org/wiki/Line_level
the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --

Wow! You have a calculator that goes to 32 significant digits? My old HP15C
is only good for about 15. You can calculate the distance to Alpha Centauri
to the nearest tenth of an inch...:^)

It was the calculator build into WinXP.

Peace,
Paul

[Scott Dorsey]

PStamler wrote:
On Nov 18, 8:39=A0pm, Randy Yates wrote:
=A0 1. If you backtrack to 0 dB from this wikipedia article
=A0 =A0http://en.wikipedia.org/wiki/Line_level
=A0 the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
=A0 respectively. Is this correct? Are the reference levels I've given
=A0 here exact?

No and yes, respectively. The reference level for dBu is actually
0.77459666924148337703585307995648V, according to my calculator --
that's the voltage equivalent of 1mW into a 600 ohm load. The
reference level for dBV is exactly 1V.

=A0 2. Is there a standard for converting from dBFS to dBu? If so, =A0 =
what is it?

No. There's an informal standard used in the film industry and in many
broadcast applications of +4dBu =3D -20dBFS, but it's never been
codified as an official standard. The informal standard, though, is (I
believe) based on an rms scale -- in other words, a tone that would
read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct
me if I'm wrong on that last bit, but that's what I think is the case.

This is sort of like asking if there is a standard for converting pounds
to feet. They aren't measuring the same thing. If you know something
specific about the item being measured, you can make some good estimates,
but you need to know something more.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

On Nov 18, 9:39*pm, Randy Yates wrote:

* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
* respectively. Is this correct? Are the reference levels I've given
* here exact?

Exact for dBV, close enough for engineering purposes for dBu.

* 2. Is there a standard for converting from dBFS to dBu?

No. This is a great point of confusion. You can't directly convert
them because they describe different kinds of units. It's like
converting the number of apples in a bushel to the number of potatoes
in a bushel. There are a few conventions, however, but mostly there's
things that you choose for yourself, not a standard to which a
manufacturer adheres. Back when people had VU meters and digital
recorders had readable meter scales and an adjustable input level
control, there was often a mark typically somewhere between -16 and
-20 dBFS on the digital meter that was the recommended point
corresponding to 0 VU. But it's rare to see that any more. If you're
working with 24-bit converters and material with fairly high dynamic
range, I'd recommend 0 VU (at whatever level that represents) provides
a record level of -20 dBFS. But it's up to you.

One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No specification or standard, but since most gear you'll find today
operates from a +/- 15 volt power supply, it's rare to find a maximum
output level before clipping much higher than +24 dBu. There are
exceptions, of course.

You'll find some discussion of these issues in the Gozintas and
Gozoutas and Meter Madness articles in the Technical Articles section
of my web site. http://mikeriversaudio.wordpress.com

[Randy Yates]

Mike Rivers writes:

On Nov 18, 9:39Â*pm, Randy Yates wrote:

Â* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
Â* respectively. Is this correct? Are the reference levels I've given
Â* here exact?

Exact for dBV, close enough for engineering purposes for dBu.

Right. As Paul said, dBu reference is the voltage corresponding
to 1 mW into 600 ohms. I knew this - just temporarily forgot ().

Â* 2. Is there a standard for converting from dBFS to dBu?

No. This is a great point of confusion. You can't directly convert
them because they describe different kinds of units. It's like
converting the number of apples in a bushel to the number of potatoes
in a bushel.

Well, yeah, I didn't mean that way. What I meant to ask is if
there is a standard way to map the full-scale output of a DAC
(or input of an ADC) to a specific voltage voltage level.

There are a few conventions, however, but mostly there's things that
you choose for yourself, not a standard to which a manufacturer
adheres. Back when people had VU meters and digital recorders had
readable meter scales and an adjustable input level control, there was
often a mark typically somewhere between -16 and -20 dBFS on the
digital meter that was the recommended point corresponding to 0 VU.

And 0 VU correspondings to +4dBu?

But it's rare to see that any more. If you're working with 24-bit
converters and material with fairly high dynamic range, I'd recommend
0 VU (at whatever level that represents) provides a record level of
-20 dBFS. But it's up to you.

That's the same translation Paul mentioned: +4dBu = -20 dBFS.

No one has yet answered the question about whether it's FS sine
or FS square.

One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output?

No specification or standard, but since most gear you'll find today
operates from a +/- 15 volt power supply, it's rare to find a maximum
output level before clipping much higher than +24 dBu. There are
exceptions, of course.

Thank you, Mike.

You'll find some discussion of these issues in the Gozintas and
Gozoutas and Meter Madness articles in the Technical Articles section
of my web site. http://mikeriversaudio.wordpress.com

OK, great. Thanks for the pointers, Mike.
--
Randy Yates % "Midnight, on the water...
Digital Signal Labs % I saw... the ocean's daughter."
% 'Can't Get It Out Of My Head'
http://www.digitalsignallabs.com % *El Dorado*, Electric Light Orchestra

[Mike Rivers]

On 11/19/2010 10:09 AM, Randy Yates wrote:

What I meant to ask is if
there is a standard way to map the full-scale output of a DAC
(or input of an ADC) to a specific voltage voltage level.

Nope.

There are a few conventions, however, but mostly there's things that
you choose for yourself, not a standard to which a manufacturer
adheres. Back when people had VU meters and digital recorders had
readable meter scales and an adjustable input level control, there was
often a mark typically somewhere between -16 and -20 dBFS on the
digital meter that was the recommended point corresponding to 0 VU.

And 0 VU correspondings to +4dBu?

Another point of great confusion. 0 VU is whatever nominal
operating level is. On "pro" equipment, it's usually +4 dBu.
On "semi-pro" equipment, it's usually -10 dBV. On some phone
company, it's +8 dBm (a unit of power, not voltage, but
usually into 600 ohms, so you can calculate the voltage). On
a consumer tape deck, who the heck knows? Usually somewhere
around -20 dBu.

That's the same translation Paul mentioned: +4dBu = -20 dBFS.

Yup, he's a smart feller.

No one has yet answered the question about whether it's FS sine
or FS square.

It doesn't really matter until you want to find the RMS
value of the waveform that got you to that digital level. If
0dBFS = +24 dBu, either a square wave or a sine wave with
the same peak value will get you there.

The RMS value of a sine wave is 0.707 (1/2 the square root
of 2) times the peak amplitude. The RMS value of a square
wave is the same as the peak amplitude.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Don Pearce[_3_]]

On Thu, 18 Nov 2010 21:19:50 -0500, Randy Yates
wrote:

Dear Audio Professionals,

Questions on levels:

1. If you backtrack to 0 dB from this wikipedia article

http://en.wikipedia.org/wiki/Line_level

the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS,
respectively. Is this correct? Are the reference levels I've given
here exact?

2. Is there a standard for converting from dBFS to dBu? If so,
what is it?

3. If the answer to 2 is yes, then does that standard use FS sine
or FS square?

Thanks for any insights.

I'm a little confused. You work in a signals lab - I would be
recommending you ask yourself.

Anyway, Q1. 0dBu is the voltage level that would have produced 1mW in
a 600 ohm system (0dBm). so it is sqrt(600 * .001), or sqrt (0.6),
which is as you say 0.775 volts.

Q2. No. FS is what you make it. It is a peak measurement, not an RMS
one, so there is no direct correlation between dBu and dBFS for a
musical waveform. You can get somewhere near it by specifying a given
crest factor but that is still at best an approximation. The best you
can probably do is to specify in terms of the peak/RMS (root 2) of a
sine wave.

The square wave case is very artificial, and results in an apparent
ability to fit an oversized sine component into a smaller space, but
this is strictly for the square case, and can be ignored for practical
purposes.

d