[Mr.T]

"Randy Yates" wrote in message
...
Descriptionism in scientific and technical fields leads to chaos.

Yes, or maybe it just sorts the technically competent from the
technically
illiterate.
As is the case here.

And maybe you need to stop having sex with your mother while she's
in between customers.

Well THAT reply sure sorted out YOUR level of intelligence anyway.

MrT.

[hank alrich]

"Mr.T" MrT@home wrote:

"Randy Yates" wrote in message
...
Descriptionism in scientific and technical fields leads to chaos.

Yes, or maybe it just sorts the technically competent from the
technically
illiterate.
As is the case here.

And maybe you need to stop having sex with your mother while she's
in between customers.

Well THAT reply sure sorted out YOUR level of intelligence anyway.

Maybe he's just talking from his own familial experience.

(This whole non****ing thread has gotten way beyond rediculous. Y'all
get yer ****in' meters and measure what you need to measure. Then go
fishing.)

--
ha
Iraq is Arabic for Vietnam

[Mark]

On Oct 24, 5:06 pm, Mike Rivers wrote:
On Oct 24, 5:04 pm, Mark wrote:

maybe real world cases in audio land....
but not true of real world cases in RF land where most things are
power into /out of 50 Ohms

Please note that you're posting to rec.AUIDO.pro and rec.AUDIO.tech.
If you want to talk about RF, please post to rec.RF.bs

100 Watts RMS is also unfortunatley common but is always a mistake
because it is mathematically incorrect.

All right, what's wrong now?

It is correct to say RMS voltage.
It is correct to say RMS current.
It is correct to say AVERAGE power.
It is not correct to say RMS power.

RMS Voltage squared/resistance = AVERAGE power.

RMS Voltage x RMS current = AVERAGE power.

RMS current squared x reistance = AVERAGE power.


Mark

[Paul Stamler]

"Randy Yates" wrote in message
...

Maybe? How many authoritative sources do you need to see it defined in
before you concur that it IS a power ratio?

Again, you're begging the question of what the meaning of "is" is.

How about if we start tugging on the definition of watt (1
joule/second). "Well, *maybe* it refers to 1 joule / second, but
Webermatic had a manufacturing problem 10 years ago in their power meter
product in which it registered 1.1 joules/second, so now we don't really
know what it means." Or, "John C. PowerEngineer used it for energy in
his report to the DOE 4 years ago and it has now become common practice
that it refers to ENERGY."

Descriptionism in scientific and technical fields leads to chaos.

Not if the vast majority of practitioners agree about what they're
measuring. Communication is about terms that are mutually agreed-upon, and
the vast majority of people working in audio agree about dBu as a way to
express a voltage measurement. So communication takes place.

Peace,
Paul

[Paul Stamler]

"Randy Yates" wrote in message
...
"Mr.T" MrT@home writes:

"Randy Yates" wrote in message
...
Descriptionism in scientific and technical fields leads to chaos.

Yes, or maybe it just sorts the technically competent from the
technically
illiterate.
As is the case here.

And maybe you need to stop having sex with your mother while she's
in between customers.

Plonk.

Peace,
Paul

[Don Pearce]

On Wed, 24 Oct 2007 19:29:50 -0700, Mark wrote:

On Oct 24, 5:06 pm, Mike Rivers wrote:
On Oct 24, 5:04 pm, Mark wrote:

maybe real world cases in audio land....
but not true of real world cases in RF land where most things are
power into /out of 50 Ohms

Please note that you're posting to rec.AUIDO.pro and rec.AUDIO.tech.
If you want to talk about RF, please post to rec.RF.bs

100 Watts RMS is also unfortunatley common but is always a mistake
because it is mathematically incorrect.

All right, what's wrong now?

It is correct to say RMS voltage.
It is correct to say RMS current.
It is correct to say AVERAGE power.
It is not correct to say RMS power.

RMS Voltage squared/resistance = AVERAGE power.

RMS Voltage x RMS current = AVERAGE power.

RMS current squared x reistance = AVERAGE power.


Mark


Absolutely spot on. Full marks to that man!

d

--
Pearce Consulting
http://www.pearce.uk.com

[Eeyore]

"Mr.T" wrote:

"Eeyore" wrote in message

NO. Energy and power are perfectly well defined.

Wasn't that his point! No need to accept new definitions caused by incorrect
usage.

There's nothing incorrect about using dBs for voltage.

Indeed since audio no longer uses matched impedance working (and hasn't fro many
decades), using dBm is not only pointless and irrelevant but wholly WRONG.

Graham

[Eeyore]

Randy Yates wrote:

"Mr.T" MrT@home writes:
"Randy Yates" wrote in message

Descriptionism in scientific and technical fields leads to chaos.

Yes, or maybe it just sorts the technically competent from the technically
illiterate.
As is the case here.

And maybe you need to stop having sex with your mother while she's
in between customers

CRETIN.

[Eeyore]

Randy Yates wrote:

Eeyore writes:
[...]
Energy and power are perfectly well defined.

Precisely. And so are decibels.

As either voltage or current or power or indeed any other unit you care to
mention.

Graham

[Mike Rivers]

On Oct 24, 10:29 pm, Mark wrote:

It is correct to say RMS voltage.
It is correct to say RMS current.
It is correct to say AVERAGE power.
It is not correct to say RMS power.

Ah, yes, you're preaching to the wrong group again. This is another
case where common use within a specific genre has expanded, or rather,
overtaken the original definition.

In audio, we usually only use RMS on spec sheets, and in this
business, spec sheets are products of the Marketing department, not
the Engineering department. There's a way to calculate RMS voltage or
current using the definition, but for anything other than a simple and
periodic waveform, it's pretty difficult to calculate. So we use "RMS"
to mean "the average voltage, current, OR POWER measured or calculated
for a sine wave."

Most people who know enough to be dangerous will tell you that RMS is
0.707 x peak, and this is true for the special case of a sine wave.
This falls down when the waveform is music, speech, or anything
complex. But since people who write spec sheets usually use sine wave
measurements, for this special case (which is understood by the
virtual "everybody") it's valid.

There aren't too many people who connect the output of an amplifier to
a resistor, put the resistor in a bucket of water, play some music
into it, and see how much the water heats up. That'll tell you the RMS
power.

[Don Pearce]

On Thu, 25 Oct 2007 03:48:52 -0700, Mike Rivers
wrote:

On Oct 24, 10:29 pm, Mark wrote:

It is correct to say RMS voltage.
It is correct to say RMS current.
It is correct to say AVERAGE power.
It is not correct to say RMS power.

Ah, yes, you're preaching to the wrong group again. This is another
case where common use within a specific genre has expanded, or rather,
overtaken the original definition.

In audio, we usually only use RMS on spec sheets, and in this
business, spec sheets are products of the Marketing department, not
the Engineering department. There's a way to calculate RMS voltage or
current using the definition, but for anything other than a simple and
periodic waveform, it's pretty difficult to calculate. So we use "RMS"
to mean "the average voltage, current, OR POWER measured or calculated
for a sine wave."

Most people who know enough to be dangerous will tell you that RMS is
0.707 x peak, and this is true for the special case of a sine wave.
This falls down when the waveform is music, speech, or anything
complex. But since people who write spec sheets usually use sine wave
measurements, for this special case (which is understood by the
virtual "everybody") it's valid.

There aren't too many people who connect the output of an amplifier to
a resistor, put the resistor in a bucket of water, play some music
into it, and see how much the water heats up. That'll tell you the RMS
power.

No it won't. It will tell you the average power.

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mike Rivers]

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

Remember IHF Music Power?

[Don Pearce]

On Thu, 25 Oct 2007 04:14:12 -0700, Mike Rivers
wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

But they would be wrong. We are supposed to be experts on this group,
so we have no excuse for misusing the technical terms.

Remember IHF Music Power?


Oh yes. Unfortunately

d

--
Pearce Consulting
http://www.pearce.uk.com

[Randy Yates]

"Paul Stamler" writes:

"Randy Yates" wrote in message
...

Maybe? How many authoritative sources do you need to see it defined in
before you concur that it IS a power ratio?

Again, you're begging the question of what the meaning of "is" is.

So are you.

How about if we start tugging on the definition of watt (1
joule/second). "Well, *maybe* it refers to 1 joule / second, but
Webermatic had a manufacturing problem 10 years ago in their power meter
product in which it registered 1.1 joules/second, so now we don't really
know what it means." Or, "John C. PowerEngineer used it for energy in
his report to the DOE 4 years ago and it has now become common practice
that it refers to ENERGY."

Descriptionism in scientific and technical fields leads to chaos.

Not if the vast majority of practitioners agree about what they're
measuring.

In the case of the bel, they don't. And in that situation, I'll take
the definition that has long been established in black-and-white over
current individual preference.

I'll accede that my assertion was perhaps too broad ( "intellectual
property"). But in the case of fundamental physical quantities, I think
it is accurate. Can you cite a counter-example?

Communication is about terms that are mutually agreed-upon, and the
vast majority of people working in audio agree about dBu as a way to
express a voltage measurement. So communication takes place.

I never said it wasn't a way to express voltage. I just said it is
indirectly voltage, and directly power.

One other aspect of my perspective that hasn't yet been mentioned: The
fruitfulness of it. If you always go back to the definition of a bel
as the log of a ratio of powers, then you avoid the confusion that
seems to regularly pop up on the subject.
--
% Randy Yates % "Remember the good old 1980's, when
%% Fuquay-Varina, NC % things were so uncomplicated?"
%%% 919-577-9882 % 'Ticket To The Moon'
%%%% % *Time*, Electric Light Orchestra
http://www.digitalsignallabs.com

[Randy Yates]

(Don Pearce) writes:

On Thu, 25 Oct 2007 04:14:12 -0700, Mike Rivers
wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

But they would be wrong. We are supposed to be experts on this group,
so we have no excuse for misusing the technical terms.

If one takes the "RMS" in "RMS Power" as applying to the voltage that is
used to calculate that power, then it makes some sense.

But I'm not really arguing we keep the term. Having been a rock musician
in the 70's (can you say MiniMoog?), it is nostalgic for me.
--
% Randy Yates % "I met someone who looks alot like you,
%% Fuquay-Varina, NC % she does the things you do,
%%% 919-577-9882 % but she is an IBM."
%%%% % 'Yours Truly, 2095', *Time*, ELO
http://www.digitalsignallabs.com

[Don Pearce]

On Thu, 25 Oct 2007 07:31:52 -0400, Randy Yates
wrote:

(Don Pearce) writes:

On Thu, 25 Oct 2007 04:14:12 -0700, Mike Rivers
wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

But they would be wrong. We are supposed to be experts on this group,
so we have no excuse for misusing the technical terms.

If one takes the "RMS" in "RMS Power" as applying to the voltage that is
used to calculate that power, then it makes some sense.


That makes no sense at all. What makes sense is to say the average
power, as that is precisely what you are measuring. Anyway, while 90%
of people understand vaguely what the word average means; I bet not
0.01% could tell you what RMS means.

But I'm not really arguing we keep the term. Having been a rock musician
in the 70's (can you say MiniMoog?), it is nostalgic for me.

I can do better than that - I can say Mellotron!

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mike Rivers]

On Oct 25, 7:24 am, Randy Yates wrote:

Not if the vast majority of practitioners agree about what they're
measuring.

In the case of the bel, they don't. And in that situation, I'll take
the definition that has long been established in black-and-white over
current individual preference.

What "vast majority" are you talking about? I'll bet there are more
guitar players than there are RF engineers. In what units would you
state the output level of a microphone preamp, and to whom? I know you
don't want to accept that anything with dB in it can be "units," but
that's what dBu is.

I completely agree that stating "Maximum output: 22 dB" is completely
wrong, but "Maximum output: +22 dBu" is completely understood and, in
my world, correct.

I never said it wasn't a way to express voltage. I just said it is
indirectly voltage, and directly power.

But nobody cares about power when speaking about interfacing devices
that produce and sink negligible power. It's the voltage that's
important. If there's an ambiguous usage, it's in saying "Gain: 60 dB"
rather than "Voltage gain: 60 dB." But in the world of voltage
interfacing of audio equipment, "voltage" is understood. When using
impedance-matched connections, it's understood that the open circuit
voltage will drop in half when (properly) loaded. But within
relatively small confines, the load impedance is high enough so that
voltage drop will be insignificant.

One other aspect of my perspective that hasn't yet been mentioned: The
fruitfulness of it. If you always go back to the definition of a bel
as the log of a ratio of powers, then you avoid the confusion that
seems to regularly pop up on the subject.

I'd hardly think the confusion regularly pops up. It only pops up when
someone tries to talk about devices that involve power, and usually
outside the context of audio interface. Unless you think that everyone
who talks about audio interfacing is hopelessly confused and none of
the numbers they've been using for years are valid. You'd have a hard
time with that argument.

It's like someone from Great Britain goes into a bar where there's a
Redskins game on TV and asks for them to change the channel to one
with a football game. That's essentially what you're doing here. Go
back to your own bar and leave us alone in our well understood
befuddlement .

[Randy Yates]

(Don Pearce) writes:

On Thu, 25 Oct 2007 07:31:52 -0400, Randy Yates
wrote:

(Don Pearce) writes:

On Thu, 25 Oct 2007 04:14:12 -0700, Mike Rivers
wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

But they would be wrong. We are supposed to be experts on this group,
so we have no excuse for misusing the technical terms.

If one takes the "RMS" in "RMS Power" as applying to the voltage that is
used to calculate that power, then it makes some sense.


That makes no sense at all. What makes sense is to say the average
power, as that is precisely what you are measuring. Anyway, while 90%
of people understand vaguely what the word average means; I bet not
0.01% could tell you what RMS means.

0.01% of the people here on this group? You must have some trick up
your sleeve.

RMS = root-mean-square, the square root of the mean of the square. In
general, given a function f(t), the RMS value F of f(t) is

F = limit as T approaches infinity ((1/T) * integral from -T/2 to +T/2 f^2(t) dt)^(1/2))

But I'm not really arguing we keep the term. Having been a rock musician
in the 70's (can you say MiniMoog?), it is nostalgic for me.

I can do better than that - I can say Mellotron!

As in, you owned one? That's cool. I think I had a 10-second opportunity
to pound on one in a music store once - it was very eery.
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..."
%%% 919-577-9882 %
%%%% % 'Eldorado Overture', *Eldorado*, ELO
http://www.digitalsignallabs.com

[Don Pearce]

On Thu, 25 Oct 2007 07:49:09 -0400, Randy Yates
wrote:

(Don Pearce) writes:

On Thu, 25 Oct 2007 07:31:52 -0400, Randy Yates
wrote:

(Don Pearce) writes:

On Thu, 25 Oct 2007 04:14:12 -0700, Mike Rivers
wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

But they would be wrong. We are supposed to be experts on this group,
so we have no excuse for misusing the technical terms.

If one takes the "RMS" in "RMS Power" as applying to the voltage that is
used to calculate that power, then it makes some sense.


That makes no sense at all. What makes sense is to say the average
power, as that is precisely what you are measuring. Anyway, while 90%
of people understand vaguely what the word average means; I bet not
0.01% could tell you what RMS means.

0.01% of the people here on this group? You must have some trick up
your sleeve.


No, people generally. I'm thinking about what you read on glossy
brochures in shops.

RMS = root-mean-square, the square root of the mean of the square. In
general, given a function f(t), the RMS value F of f(t) is

F = limit as T approaches infinity ((1/T) * integral from -T/2 to +T/2 f^2(t) dt)^(1/2))

But I'm not really arguing we keep the term. Having been a rock musician
in the 70's (can you say MiniMoog?), it is nostalgic for me.

I can do better than that - I can say Mellotron!

As in, you owned one? That's cool. I think I had a 10-second opportunity
to pound on one in a music store once - it was very eery.

Yup. I think it was about tenth hand and the tapes had snapped and
been re-attached so many times that most of the keys only managed a
couple of seconds.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Anahata]

Randy Yates wrote:

If one takes the "RMS" in "RMS Power" as applying to the voltage that is
used to calculate that power, then it makes some sense.

Not much.

The *only* thing that makes technical sense and is truly compatible with
the intention behind "RMS power" is to say "sine wave power". If only
that was the standard way of describing am amplifier rating, we'd all be
talking about the same thing and we wouldn't have to waste time arguing
about the misapplication of the term "RMS".

If you refined that to PURE sine wave Marketing might even be happy
about the implied pristine quality too.

It's often forgotten in these discussions that the power an amplifier
can deliver at clipping point varies with waveform. An amplifier with
100W max sine wave output could deliver 200W square wave, and that would
be real honest power, whether measured by heating effect or calculated
from the RMS voltage. As mentioned before, that 0.707 ratio holds only
for sine waves.

Anahata

[Randy Yates]

Mike Rivers writes:
[...]
On Oct 25, 7:24 am, Randy Yates wrote:
I never said it wasn't a way to express voltage. I just said it is
indirectly voltage, and directly power.

But nobody cares about power when speaking about interfacing devices
that produce and sink negligible power. It's the voltage that's
important.

This is a damned-confusing situation semantically.

I agree that dBu is used to specify voltage. But dBu is the log of a
ratio of powers.

FURTHER, dBu has NO units. 20*log(V1/VR), when V1 and VR are both in
volts, is unitless.

We could also say, assuming for example a resistance of 1 ohm, that the
voltage at a point in a circuit is 10 milliwatts, meaning that it is the
voltage that would produce 10 milliwatts into a 1 ohm resistance. No,
we're not interested in watts but we're deriving the quantity we are
interested in, volts, through it.

Such is the situation with dBu (and similarly with other dB "units").

And don't give me the "watts are not volts" argument. Volts are not
[] (nothing, unitless), either!

Our minds are wonderful things - they can take this complex situation
and arrive at the "important information" almost instantly. But if we
forget this fact (that it is most directly a ratio of powers), we may
also forget how to manipulate the quantities involved properly.
--
% Randy Yates % "Midnight, on the water...
%% Fuquay-Varina, NC % I saw... the ocean's daughter."
%%% 919-577-9882 % 'Can't Get It Out Of My Head'
%%%% % *El Dorado*, Electric Light Orchestra
http://www.digitalsignallabs.com

[Laurence Payne]

On Thu, 25 Oct 2007 11:55:57 GMT, (Don Pearce)
wrote:

That makes no sense at all. What makes sense is to say the average
power, as that is precisely what you are measuring. Anyway, while 90%
of people understand vaguely what the word average means; I bet not
0.01% could tell you what RMS means.

0.01% of the people here on this group? You must have some trick up
your sleeve.


No, people generally. I'm thinking about what you read on glossy
brochures in shops.

Even punters often have a vague idea that RMS is real, other figures
are marketing-speak, even if they don't know the technicalities.

[Don Pearce]

On Thu, 25 Oct 2007 08:21:57 -0400, Randy Yates
wrote:

Mike Rivers writes:
[...]
On Oct 25, 7:24 am, Randy Yates wrote:
I never said it wasn't a way to express voltage. I just said it is
indirectly voltage, and directly power.

But nobody cares about power when speaking about interfacing devices
that produce and sink negligible power. It's the voltage that's
important.

This is a damned-confusing situation semantically.

I agree that dBu is used to specify voltage. But dBu is the log of a
ratio of powers.

No, the dBu is the log of the ratio of what used to be powers, but is
now voltage.


FURTHER, dBu has NO units. 20*log(V1/VR), when V1 and VR are both in
volts, is unitless.


dBu IS the unit (inclusive of its dimension)

We could also say, assuming for example a resistance of 1 ohm, that the
voltage at a point in a circuit is 10 milliwatts, meaning that it is the
voltage that would produce 10 milliwatts into a 1 ohm resistance. No,
we're not interested in watts but we're deriving the quantity we are
interested in, volts, through it.

Derived units are always tricky.

Such is the situation with dBu (and similarly with other dB "units").

And don't give me the "watts are not volts" argument. Volts are not
[] (nothing, unitless), either!

Our minds are wonderful things - they can take this complex situation
and arrive at the "important information" almost instantly. But if we
forget this fact (that it is most directly a ratio of powers), we may
also forget how to manipulate the quantities involved properly.

For most of the audio chain it is the voltage, not the power that
matters (to us, semantically, that is - to the electronics the power
always matters). Where that assumption fails is at the ends of the
chain - the microphone and the speakers. For the speakers the need for
a power rating is obvious, but it may be less so for a microphone. But
in defining the signal to noise ratio you get off a microphone, what
you need is the ratio of signal power to noise power, and you have to
juggle impedances to optimize that ratio. Unfortunately the specs tend
to be written in voltage terms, so if you want to do any meaningful
calculations, you have to translate.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Don Pearce]

On Thu, 25 Oct 2007 13:29:53 +0100, Laurence Payne
NOSPAMlpayne1ATdsl.pipex.com wrote:

On Thu, 25 Oct 2007 11:55:57 GMT, (Don Pearce)
wrote:

That makes no sense at all. What makes sense is to say the average
power, as that is precisely what you are measuring. Anyway, while 90%
of people understand vaguely what the word average means; I bet not
0.01% could tell you what RMS means.

0.01% of the people here on this group? You must have some trick up
your sleeve.


No, people generally. I'm thinking about what you read on glossy
brochures in shops.

Even punters often have a vague idea that RMS is real, other figures
are marketing-speak, even if they don't know the technicalities.

Well, they obviously don't know it is real, because it isn't. But they
may feel that it is a "trustworthy" number. They still couldn't tell
you what it actually means though.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Eeyore]

Mike Rivers wrote:

On Oct 25, 6:53 am, (Don Pearce) wrote:

Mathematically it is possible to take the RMS of power, but I have no
idea what you might do with the figure you end up with, because it has
no possible meaning that I'm aware of.

Did you read what I wrote about marketing? THAT'S the real world that
we're in here. "RMS Power" looks good to those reading the spec sheet.
If it said "Average power" the reader would think the company is
trying to pull a fast one. Actually, they mostly just say "Power" or
"Maximum power" which is even less meaningful.

At least if you measure RMS voltage of a sine wave going into a
resistor, you can compute a number that agrees with what you see on
the spec sheet. Most people would call that "RMS Power" if they called
it anything other than "power."

Remember IHF Music Power?

I think you've missed what Don was trying to explain.

RMS has a precise mathematical definition (root mean square) as does average.

When you multiply RMS volts by RMS amps you get AVERAGE watts. RMS watts would
be something else and largely meaningless. It confused me for some years too.

Graham

[Eeyore]

Randy Yates wrote:

FURTHER, dBu has NO units. 20*log(V1/VR), when V1 and VR are both in
volts, is unitless.

That's not how you calculate dBu.

dBu = 20log10(signal_voltage/0.775V).

Graham

[Mike Rivers]

On Oct 25, 8:33 am, (Don Pearce) wrote:

Even punters often have a vague idea that RMS is real, other figures
are marketing-speak, even if they don't know the technicalities.

Well, they obviously don't know it is real, because it isn't. But they
may feel that it is a "trustworthy" number. They still couldn't tell
you what it actually means though.

That's moving toward a good point about being "trustworthy." They tend
to use that number as a means of comparison between similar products.
But if it's truly meaningless, the one with the bigger number could
deliver less usable power than the one with the smaller number. This
has been true more than we'd like to know about.

The good news is that most reputable manufacturers make the
measurement in the same way - continuous sine wave, probably around 1
kHz or so - so the data is comparable. But a power amplifier with a
skimpy power supply might have an impressive "RMS Power" number be
inadequate for driving a subwoofer because power supply poops out in
less than a single cycle at lower frequencies.

[Mike Rivers]

On Oct 25, 8:21 am, Randy Yates wrote:

I agree that dBu is used to specify voltage. But dBu is the log of a
ratio of powers.

No, dBu is 20 times the log of the ratio of the measured voltage and
0.775 volts. Since you don't know the current or impedance, you have
no idea what the power is.

You aren't one of those people who confused dB, dBu, and dBm are you?
That's another can of worms since in audio, dBm is nearly always
measured with a 600 ohm source and load and in RF, it's most commonly
50 ohms. Watts is always watts, but when you want to know how many
volts you have across that 600 or 50 ohm load, it's different. And in
low level audio interfacing, we like to talk about volts.

FURTHER, dBu has NO units.

This is true in itself, but if you know the number of dBu, you can, if
you actually want to, easily and unambiguously calculate the number of
volts. And since we're often interested in voltage gain, knowing the
input and output as a ratio to a standard reference, calculating
voltage is simple subtraction. It's just a convenient way of working
if everyone plays by the same rules.

We could also say, assuming for example a resistance of 1 ohm, that the
voltage at a point in a circuit is 10 milliwatts, meaning that it is the
voltage that would produce 10 milliwatts into a 1 ohm resistance.

Why in the world would we say that? Volts is volts, watts is watts.
What we DID say is that we'll call 0 dBu the voltage measured across a
600 ohm resistor when 1 milliwatt is delivered to that resistor. But
that doesn't mean you can connect a 600 ohm load across a device
that's putting out 0.775 open circuit and expect to measure 1.29
milliamps (or 1 milliwatt).

Our minds are wonderful things - they can take this complex situation
and arrive at the "important information" almost instantly. But if we
forget this fact (that it is most directly a ratio of powers), we may
also forget how to manipulate the quantities involved properly.

They can also take a simple and easily understood concept and make it
hopelessly meaningless just by insisting that a definition is
incorrectly used.

[Eeyore]

Mike Rivers wrote:

Randy Yates wrote:

FURTHER, dBu has NO units.

This is true in itself

Actually it's not. The units of dBu are Volts. In units of magnitude of 0.775.

Graham

[Randy Yates]

Eeyore writes:

Mike Rivers wrote:

Randy Yates wrote:

FURTHER, dBu has NO units.

This is true in itself

Actually it's not. The units of dBu are Volts. In units of magnitude
of 0.775.

Wow. Utterly amazing. I actually thought you knew better, too, Eeyore.

The amount of insanity and chaos on this topic is scary.
--
% Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven.
%% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and
%%% 919-577-9882 % Verdi's always creepin' from her room."
%%%% % "Rockaria", *A New World Record*, ELO
http://www.digitalsignallabs.com

[Eeyore]

Randy Yates wrote:

Eeyore writes:
Mike Rivers wrote:
Randy Yates wrote:

FURTHER, dBu has NO units.

This is true in itself

Actually it's not. The units of dBu are Volts. In units of magnitude
of 0.775.

Wow. Utterly amazing. I actually thought you knew better, too, Eeyore.

The amount of insanity and chaos on this topic is scary.

You're seriously out of touch with reality. dBu are no different from dBV aside from an small
offset of ~ 2.2dB.

X dBu = X-2.2 dBV.

How do you explain dBV and dB SPL in your power-centric world ?

Graham

[Mike Rivers]

On Oct 25, 11:22 am, Eeyore
wrote:

The units of dBu are Volts. In units of magnitude of 0.775.

I was gong to say that, but I figured Mr. Semantic would give me an
argument. Let him argue with you for a change.

When you look at it as arithmetic, it actually has no units: Volts
divided by volts is unitless (as opposed to volts plus volts). What we
can (and do) say, however, is that 0 dBu (a specific number) equals
0.775 volts. That's not precisely the same as dBu equals volts.

[Ian Iveson]

Don Pearce wrote

...
Mathematically it is possible to take the RMS of power,
but I have no
idea what you might do with the figure you end up with,
because it has
no possible meaning that I'm aware of.

You may wish to describe its statistical distribution in
time, or with respect to some other variable. Its standard
deviation or variance, for example.

Unlike the average, the rms of power would not be zero for a
capacitance or inductance. How that might be useful I don't
know.

Ian

[Randy Yates]

Mike Rivers writes:

On Oct 25, 11:22 am, Eeyore
wrote:

The units of dBu are Volts. In units of magnitude of 0.775.

I was gong to say that, but I figured Mr. Semantic would give me an
argument. Let him argue with you for a change.

When you look at it as arithmetic, it actually has no units: Volts
divided by volts is unitless (as opposed to volts plus volts). What we
can (and do) say, however, is that 0 dBu (a specific number) equals
0.775 volts. That's not precisely the same as dBu equals volts.

This discussion has been very revealing.
--
% Randy Yates % "And all that I can do
%% Fuquay-Varina, NC % is say I'm sorry,
%%% 919-577-9882 % that's the way it goes..."
%%%% % Getting To The Point', *Balance of Power*, ELO
http://www.digitalsignallabs.com

[Romeo Rondeau[_2_]]

Randy Yates wrote:
Mike Rivers writes:

On Oct 25, 11:22 am, Eeyore
wrote:

The units of dBu are Volts. In units of magnitude of 0.775.
I was gong to say that, but I figured Mr. Semantic would give me an
argument. Let him argue with you for a change.

When you look at it as arithmetic, it actually has no units: Volts
divided by volts is unitless (as opposed to volts plus volts). What we
can (and do) say, however, is that 0 dBu (a specific number) equals
0.775 volts. That's not precisely the same as dBu equals volts.

This discussion has been very revealing.


Why don't you guys just measure your dicks and be done with it :-)

[Randy Yates]

Romeo Rondeau writes:

Why don't you guys just measure your dicks and be done with it :-)

Should we use the dBD scale? (Gives new meaning to dBV...)
--
% Randy Yates % "With time with what you've learned,
%% Fuquay-Varina, NC % they'll kiss the ground you walk
%%% 919-577-9882 % upon."
%%%% % '21st Century Man', *Time*, ELO
http://www.digitalsignallabs.com

[Randy Yates]

Les Cargill writes:

They're baaaaaaack. http://www.mellotron.com

Who'd want one now when you can have a sampler
with 24 bits / 120 dB SNR?
--
% Randy Yates % "Watching all the days go by...
%% Fuquay-Varina, NC % Who are you and who am I?"
%%% 919-577-9882 % 'Mission (A World Record)',
%%%% % *A New World Record*, ELO
http://www.digitalsignallabs.com

[[email protected]]

On Oct 25, 12:51 pm, Randy Yates wrote:
Romeo Rondeau writes:
Why don't you guys just measure your dicks and be done with it :-)

Should we use the dBD scale? (Gives new meaning to dBV...)

dB(D) is a real scale, D weighting for noise measurements near
aircraft, airports etc.

bobs

Bob Smith
BS Studios
we organize chaos
http://www.bsstudios.com

[Keith Carlson]

"Randy Yates" wrote in message
...
"Keith Carlson" writes:

Well, I know what the definition is, but I'm trying to understand where
it
comes from to help me remember it. I tend to get SPL vs sound power level
mixed up (as well as when it's 3db or 6db that represents a doubling).

The definition I know is:

SPL = 20 log (p1/p0), or 10 log (p1/p0)^2 (where "^2" means to the
power of 2)

I understand that the factor of 10 is because it's expressed in decibels
as
opposed to bels. My specific question, though, is why is the ratio
squared?
If p0 is the reference pressure level, and p1 is the measured pressure
level, why isn't SPL just the log of that ratio, similar to the way sound
power level is the log of power level ratio?

The primary reason is simply that anything involving decibels is by
definition a ratio of powers, and acoustic power is related to the
square of the pressure level.
--
% Randy Yates % "My Shangri-la has gone away, fading
like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% % 'Shangri-La', *A New World Record*, ELO
http://www.digitalsignallabs.com

Thanks, Randy, and everyone else who answered. I didn't know this one of
"those" questions that stirs up an old debate.

It helps me to know that a decibel or bel is defined as the log of a ratio
of power levels.
Gives me something to remember then, that if it's acoustic pressure, or
voltage, or anything where its square is related to power, that it's going
to be 20x rather than 10x (for decibel).

And from there I can remember figure whether it's 3dB or 6 dB that
represents (roughly) a doubling of the ratio.

[Randy Yates]

"Keith Carlson" writes:

"Randy Yates" wrote in message
...
"Keith Carlson" writes:

Well, I know what the definition is, but I'm trying to understand where
it
comes from to help me remember it. I tend to get SPL vs sound power level
mixed up (as well as when it's 3db or 6db that represents a doubling).

The definition I know is:

SPL = 20 log (p1/p0), or 10 log (p1/p0)^2 (where "^2" means to the
power of 2)

I understand that the factor of 10 is because it's expressed in decibels
as
opposed to bels. My specific question, though, is why is the ratio
squared?
If p0 is the reference pressure level, and p1 is the measured pressure
level, why isn't SPL just the log of that ratio, similar to the way sound
power level is the log of power level ratio?

The primary reason is simply that anything involving decibels is by
definition a ratio of powers, and acoustic power is related to the
square of the pressure level.
--
% Randy Yates % "My Shangri-la has gone away, fading
like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% % 'Shangri-La', *A New World Record*, ELO
http://www.digitalsignallabs.com

Thanks, Randy, and everyone else who answered. I didn't know this one of
"those" questions that stirs up an old debate.

It helps me to know that a decibel or bel is defined as the log of a ratio
of power levels.
Gives me something to remember then, that if it's acoustic pressure, or
voltage, or anything where its square is related to power, that it's going
to be 20x rather than 10x (for decibel).

And from there I can remember figure whether it's 3dB or 6 dB that
represents (roughly) a doubling of the ratio.

Exactly. I'm very glad to see you "got it," Keith. Glad I could help.
--
% Randy Yates % "Rollin' and riding and slippin' and
%% Fuquay-Varina, NC % sliding, it's magic."
%%% 919-577-9882 %
%%%% % 'Living' Thing', *A New World Record*, ELO
http://www.digitalsignallabs.com