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Randy Yates Randy Yates is offline
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Default Questions on Levels

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
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Randy Yates Randy Yates is offline
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Default Questions on Levels

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
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Randy Yates Randy Yates is offline
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Default Questions on Levels

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
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dizzy dizzy is offline
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Default Questions on Levels

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...

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PStamler PStamler is offline
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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


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PStamler PStamler is offline
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Default Questions on Levels

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
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Don Pearce[_3_] Don Pearce[_3_] is offline
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Default Questions on Levels

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
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Adrian Tuddenham[_2_] Adrian Tuddenham[_2_] is offline
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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
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Arny Krueger Arny Krueger is offline
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"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.


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Mike Rivers Mike Rivers is offline
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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



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Randy Yates Randy Yates is offline
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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
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Randy Yates Randy Yates is offline
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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
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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
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Randy Yates Randy Yates is offline
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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
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Scott Dorsey Scott Dorsey is offline
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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."


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Scott Dorsey Scott Dorsey is offline
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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."
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Scott Dorsey Scott Dorsey is offline
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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."
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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.
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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
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David Nebenzahl David Nebenzahl is offline
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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)
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Mike Rivers Mike Rivers is offline
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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
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Mike Rivers Mike Rivers is offline
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On 11/19/2010 10:22 AM, Randy Yates wrote:
Mike writes:
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.


We're getting wrapped around the axle here since I don't
know what your real question is. What you're asking is kind
of abstract.

dBFS is dB referenced to full scale which is all the bits on
dBu is dB referenced to .775 volts
dBV is dB referenced to 1 volt

Any of those can be RMS or peak. Peak is significant when
dealing with digital levels, but the only level that's
really significant is the one beyond which you can't go
higher, and that's only one level, 0 dBFS

So you're saying then it's FS sine.


If you say so. Please ask your REAL question if you have
one. Are you looking for a solution to a problem? Or trying
to interpret some marketing goof's data sheet or manual? If
you're just looking for definitions and conventions, then
you have them.


--
"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
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Randy Yates Randy Yates is offline
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Mike Rivers writes:

On 11/19/2010 10:22 AM, Randy Yates wrote:
Mike writes:
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.


We're getting wrapped around the axle here since I don't know what
your real question is. What you're asking is kind of abstract.


Is dBFS abstract? If so, then I guess I'm asking an abstract
question.

My question is this: What is the definition of dBFS?

dBFS is dB referenced to full scale which is all the bits on
dBu is dB referenced to .775 volts
dBV is dB referenced to 1 volt

Any of those can be RMS or peak.



Peak is significant when dealing with digital levels, but the only
level that's really significant is the one beyond which you can't go
higher, and that's only one level, 0 dBFS


If dBFS is defined as

dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave),

where XRMS is the RMS value of the digital data stream, and you're
generating a "digital square wave," then you are wrong. The digital
square wave can go to +3dBFS as defined above.

So you're saying then it's FS sine.


If you say so. Please ask your REAL question if you have one. Are you
looking for a solution to a problem? Or trying to interpret some
marketing goof's data sheet or manual? If you're just looking for
definitions and conventions, then you have them.


It seems that there really is no standard definition. That's the
problem. It's not a matter of abstractness, but rather of
well-definedness.
--
Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven.
Digital Signal Labs % She love the way Puccini lays down a tune, and
% Verdi's always creepin' from her room."
http://www.digitalsignallabs.com % "Rockaria", *A New World Record*, ELO
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Bill Graham Bill Graham is offline
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"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...:^)



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Mike Rivers Mike Rivers is offline
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On 11/19/2010 7:52 PM, Randy Yates wrote:

My question is this: What is the definition of dBFS?


Decibels relative to full scale. 0 dBFS is full scale,
everything else is down from there. -6 dBFS is half the
maximum number as with all the bits on.

If dBFS is defined as

dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave),

where XRMS is the RMS value of the digital data stream, and you're
generating a "digital square wave," then you are wrong. The digital
square wave can go to +3dBFS as defined above.


But it's not defined that way. In reality, you can't have
anything higher than 0 dBFS. That's where you run out of
numbers to express the amplitude. There's such a thing as
"intersample overload" where the input actually goes higher
than the 0 dBFS level between two adjacent samples, but
that's an anomaly.

It seems that there really is no standard definition. That's the
problem. It's not a matter of abstractness, but rather of
well-definedness.


The thing is that what you're concerned with in digital
recording is how much headroom you have. You can choose your
own headroom amount simply by choosing the analog reference
level that gives your desired headroom. If you're
compressing the **** out of everything, you don't need as
much headroom as if you're recording an orchestra or
something where you're unsure of the input dynamic range,
and you can choose a higher reference level. For most music,
20 dB of headroom is pretty safe, which is why the -20 dBFS
reference is fairly common.


--
"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
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Randy Yates Randy Yates is offline
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Mike Rivers writes:

On 11/19/2010 7:52 PM, Randy Yates wrote:

My question is this: What is the definition of dBFS?


Decibels relative to full scale.


Nonsense. All you've given is the meaning of the acronym, not an
engineering definition of the unit. This is similar to stating the
definition of RMS is "root mean square."

[...]
But it's not defined that way.


I'm not asking how it's not defined. I'm asking how it is defined (in a
sensible way).
--
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
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hank alrich hank alrich is offline
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Randy Yates wrote:

Is dBFS abstract?


In the sense that it correlates to no specific power or voltage level in
the analog world, yes. When we include information about the converter's
input expectations then we can link these disparate measurements.

If so, then I guess I'm asking an abstract
question.


I don't think that's the case. There are concrete answers to your
question(s), even if they wrap an abstract concept.

My question is this: What is the definition of dBFS?


Theorectically, when the last bit of dynamic range is utilized, that
will be shown by the metering as 0 dBFS. Any increase of input level
thereafter will result in clipping.

--
shut up and play your guitar * http://hankalrich.com/
http://armadillomusicproductions.com/who'slistening.html
http://www.sonicbids.com/HankandShai...withDougHarman
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hank alrich hank alrich is offline
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Randy Yates wrote:

Mike Rivers writes:

On 11/19/2010 7:52 PM, Randy Yates wrote:

My question is this: What is the definition of dBFS?


Decibels relative to full scale.


Nonsense. All you've given is the meaning of the acronym, not an
engineering definition of the unit. This is similar to stating the
definition of RMS is "root mean square."


Nope. It is exactly what Mike stated. It's the "that's all there is and
there ain't no more" point in the converter, assuming heh that the
metering and the conveter's actual performance are accurately linked.

--
shut up and play your guitar * http://hankalrich.com/
http://armadillomusicproductions.com/who'slistening.html
http://www.sonicbids.com/HankandShai...withDougHarman
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Scott Dorsey Scott Dorsey is offline
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In article , Randy Yates wrote:

If dBFS is defined as

dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave),

where XRMS is the RMS value of the digital data stream, and you're
generating a "digital square wave," then you are wrong. The digital
square wave can go to +3dBFS as defined above.


dBFS has not got a damn thing to do with sine waves or reference levels
or anything in the analogue world.

It has ONLY to do with how far a digital level is below the point at
which the digital value reaches full scale (all bits on).
--scott

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


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davew davew is offline
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On Nov 20, 2:46*am, Randy Yates wrote:
(Scott Dorsey) writes:
In article , Randy Yates wrote:


If dBFS is defined as


*dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave),


where XRMS is the RMS value of the digital data stream, and you're
generating a "digital square wave," then you are wrong. The digital
square wave can go to +3dBFS as defined above.


dBFS has not got a damn thing to do with sine waves or reference levels
or anything in the analogue world.


Again, I'm not asking how it's not defined, I'm asking how it is
defined.

You guys have danced around this one all day. It's getting humorous.

It has ONLY to do with how far a digital level is below the point at
which the digital value reaches full scale (all bits on).


If you know what it means, and you're literate, then you should be able
to come up with a precise definition. I haven't seen one yet.
--
Randy Yates * * * * * * * * * * *% "She has an IQ of 1001, she has a jumpsuit
Digital Signal Labs * * * * * * *% * * * * * *on, and she's also a telephone."
* * * * *%http://www.digitalsignallabs.com% * * * *'Yours Truly, 2095', *Time*, ELO *



ratio (dBFS) = 20log10 (magnitude / maximum possible or allowable
magnitude).

How you measure/define magnitude is the interesting question. i.e.
peak, rms, average, whatever
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Eric Jacobsen Eric Jacobsen is offline
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On Fri, 19 Nov 2010 20:32:08 -0500, Randy Yates
wrote:

Mike Rivers writes:

On 11/19/2010 7:52 PM, Randy Yates wrote:

My question is this: What is the definition of dBFS?


Decibels relative to full scale.


Nonsense. All you've given is the meaning of the acronym, not an
engineering definition of the unit. This is similar to stating the
definition of RMS is "root mean square."

[...]
But it's not defined that way.


I'm not asking how it's not defined. I'm asking how it is defined (in a
sensible way).


I think you're asking what color the sky is, and people are telling
you "blue", but you're expecting a wavelength or something, so you're
not accepting the answer.

As you know, dB measurements are always relative to some reference
level. With dBFS the reference level is Full Scale of the converter
or number system or whatever. The ratio of the level measured to the
Full Scale level provides the argument for the logarithm, and the
scaled result is dBFS.

If you can do dBm, or dBW, or dBC, you should be able to do dBFS.

The odd part is that you're not seeing this after being told correctly
what it is several times.


Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
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rickman rickman is offline
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On Nov 19, 10:42*pm, (Eric Jacobsen) wrote:
On Fri, 19 Nov 2010 20:32:08 -0500, Randy Yates
wrote:



Mike Rivers writes:


On 11/19/2010 7:52 PM, Randy Yates wrote:


My question is this: What is the definition of dBFS?


Decibels relative to full scale.


Nonsense. All you've given is the meaning of the acronym, not an
engineering definition of the unit. This is similar to stating the
definition of RMS is "root mean square."


[...]
But it's not defined that way.


I'm not asking how it's not defined. I'm asking how it is defined (in a
sensible way).


I think you're asking what color the sky is, and people are telling
you "blue", but you're expecting a wavelength or something, so you're
not accepting the answer.

As you know, dB measurements are always relative to some reference
level. * With dBFS the reference level is Full Scale of the converter
or number system or whatever. * The ratio of the level measured to the
Full Scale level provides the argument for the logarithm, and the
scaled result is dBFS.

If you can do dBm, or dBW, or dBC, you should be able to do dBFS.

The odd part is that you're not seeing this after being told correctly
what it is several times.


I think you are using an inappropriate metaphor. It is more like
Randy is asking what is the elephant like and the blind men are all
telling him something different in these two threads. One person says
0 dBFS is a sample of all 1's and all 0's is -96 dBFS (I won't even go
into what is wrong with that one)! Another describes how a VU meter
works. Yet another tells him 0 dBFS is the peak clipping point (that
one alone actually says somethng).

None of the blind men are really right and none are wrong. In the
meantime no coherent picture of the dBFS elephant has emerged and more
disjointed statements are made on the topic.

Another metaphor is that this is a can of worms!

Rick
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PStamler PStamler is offline
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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
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PStamler PStamler is offline
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I smell a troll.

When somebody asks a question and gets the precise answer from several
people at once, and keeps on arguing that nobody has given him the
answer, then a troll should be suspected.

0dBFS is the level at which one or the other extremes of a digital
waveform is at maximum codeable level. There are no established
standards relating that to any standards in the analog world, be they
dBu, dBV, dBm or any other. There are some informal standards in the
movie and broadcast world, but no standards body such as IEC or AES
has adopted an official standard.

And Randy, before you tell me "I don't want to know what isn't, I want
to know what is," what I've written above is what is (a definition of
dBFS), and there really ain't no more, and until a standards committee
gets together and votes out a standard, there won't be.

Peace,
Paul
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glen herrmannsfeldt glen herrmannsfeldt is offline
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In comp.dsp Eric Jacobsen wrote:
(snip, someone wrote)

Nonsense. All you've given is the meaning of the acronym, not an
engineering definition of the unit. This is similar to stating the
definition of RMS is "root mean square."

(snip)

I think you're asking what color the sky is, and people are telling
you "blue", but you're expecting a wavelength or something, so you're
not accepting the answer.


As you know, dB measurements are always relative to some reference
level. With dBFS the reference level is Full Scale of the converter
or number system or whatever. The ratio of the level measured to the
Full Scale level provides the argument for the logarithm, and the
scaled result is dBFS.


But there is more to it than just the reference. Well, if you
just measure one sample then that is all, but for a signal
of some duration, it is more complicated. I can, for example,
compute RMS for a whole CD track. I could also compute the
mean of the absolute value, the geometric mean of the absolute
value, or many other mathematical functions of the samples.

If I have a sine that reaches peak at exactly a sample point,
and reaches full scale at that point, then RMS is 5 log(2),
or about 1.5dB lower. For mean absolute value, 10 log(2/pi),
or about 1.96dB lower.

If you can do dBm, or dBW, or dBC, you should be able to do dBFS.


The odd part is that you're not seeing this after being told correctly
what it is several times.


-- glen
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"rickman" wrote in message
...
None of the blind men are really right and none are wrong. In the
meantime no coherent picture of the dBFS elephant has emerged and more
disjointed statements are made on the topic.



It seems to me if you realise the Bell or dB is a RELATIVE LOG term of power
(and it's constituents) ratio's with no absolute UNLESS defined as a subset,
(eg dBv, dBu, dBm etc) then asking for a SINGLE absolute point of reference,
or single definition, is simply asking for the impossible.

dBFS is simply the *Full Scale* point of ANY system so defined. IF you want
it to mean anything specific, you must define it as such.

MrT.





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