Hi,

In message , Svante
writes

My answer to this is that the original definition is for the power
ratio, and the logarithm of that power ratio was taken as a BEL. The
deci was introduced, just as for the decimeter, and we ended up with a
TEN before the log. To measure a power level difference by means of
voltages, given constant load resistance, we would have to take the
log of the SQUARE of the voltage ratio, since power is proportional to
voltage squared. Simple math makes us then realise that we can skip
the square if we put TWENTY before the log instead.

That was my reasoning also. The factor of 2 is only necessary to account
for the squared term in the relationship between power and voltage (or
their equivalents). However, having checked a few links from Google, it
seems far from clear - there are many conflicting opinions. For example:

http://www.madengineer.com/blunders/decibels.htm
Claims the decibel was originally defined to relate pressures.

http://www.sizes.com/units/decibel.htm
Claims that the decibel originated to relate powers.

Using dB for power relationships seems mathematically clear and
intuitive - the maths needs to be massaged in order to compare voltages,
for example. The same goes for sound power, and sound pressure (pressure
being the mechanical analog of voltage).


So in my mind there is no doubt that the original (deci-)bel
definition is for a power ratio, and that the equation for a voltage
ratio is derived from that.

It does seem logical; unfortunately, I can't find any definitive
reference.

--
Regards,
Glenn Booth

Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

(Dick Pierce) wrote in message . com...
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante)
wrote:

Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the
VOLTAGES that are compared (in the electrical case) not the POWERS. So
if we have a second harmonic 40 dB down, the second harmonic
distorsion is 1 %, not 0.01 %.
(In this case the voltage of the harmonic is 1% of the fundamental,
and its power is 0.01% of the fundamental)

What is the reason for this convention? I'd think that power would be
more logical.

---
It is _much_ easier to notch out the fundamental(s) and measure the
voltage of the remaining component(s) than it is to measure their power.

Then, knowing the voltage of the offending component(s) appearing across
the load and the impedance of the load at the various frequencies at
which distortion rears its ugly head, their contribution to the power
being dissipated in/by the load can be easily calculated.

Precisely. ALL of the THD meters in existance are essentially
voltmeters with filters. Going from the ancient and venerable
General Radio 1936 or Hewlett-Packard 330, through the HP 334,
through the Sound Technology 1700, Amber, Marconi and so on,
they are ALL voltmeters that have a narrow-band notch filter
in them.

Hmm, just curious, did they have circuitry to measure RMS voltage,
rather than average voltage? I guess so, because that would be crucial
to end up with a correct result. The point here is that the only
reasonable way to add up harmonics is to add their powers. That is why
the *RMS* voltage of the (sum of all) harmonics would have to be
measured.

In the standard distortion analyzers, like the HP 339, Soundtech 1700,
etc., they either use a rms circuit or an average detector to measure

^^^^^^^ Really???

Was there a question?


(a) the level of the signal under test, and (b) the level of that signal
after the fundamental has been nulled out. No one uses a power sensor to
measure distortion or signal power.

You can also use a spectrum analyzer to measure distortion. In that
case, a narrow-band measurement is made at each harmonic frequency, but
the detector used is still either a rms detector or an average detector.

So, in all cases, you are still measuring voltages, not powers, for the
simple reason that you are supplying a signal in the form of *voltage*.

So let's say that you have only two distorsion products, 2% of second
harmonic and 1% of third harmonic. How much total harmonic distortion
do you have then?

My response would be sqrt(0.02^2+0.01^2)=0.022 or 2.2%. The equation
can be seen as "calulate the powers, add them up, and convert back to
voltage".
An RMS measurement of the residual voltage would yield this value, but
if an analyser would measure AVERAGE (absolute) voltage of the
residual, the result would come out wrong, right?

An average detector rectifies the signal and takes the average. It does
not provide the same result as an rms detector, and a fudge factor is
added to make the numbers agree for sinusiodal signals. But the
difference is small. RMS detectors are the correct detector to use, but
they are more expensive. There is yet another detector, the peak
detector, that can be used, but it would give an even larger error
compared to the rms detector.

As an aside, my first job was designing a distortion analyzer many years
ago.


And, in some sense, by measuring RMS voltage the power is involved.
Not directly though, of course.

There exist some signals with certain crest factors that give
significantly different results whether you use an average detector or
rms detector. I'll leave that as an exercise to you.

Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

(Dick Pierce) wrote in message . com...
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante)
wrote:

Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the
VOLTAGES that are compared (in the electrical case) not the POWERS. So
if we have a second harmonic 40 dB down, the second harmonic
distorsion is 1 %, not 0.01 %.
(In this case the voltage of the harmonic is 1% of the fundamental,
and its power is 0.01% of the fundamental)

What is the reason for this convention? I'd think that power would be
more logical.

---
It is _much_ easier to notch out the fundamental(s) and measure the
voltage of the remaining component(s) than it is to measure their power.

Then, knowing the voltage of the offending component(s) appearing across
the load and the impedance of the load at the various frequencies at
which distortion rears its ugly head, their contribution to the power
being dissipated in/by the load can be easily calculated.

Precisely. ALL of the THD meters in existance are essentially
voltmeters with filters. Going from the ancient and venerable
General Radio 1936 or Hewlett-Packard 330, through the HP 334,
through the Sound Technology 1700, Amber, Marconi and so on,
they are ALL voltmeters that have a narrow-band notch filter
in them.

Hmm, just curious, did they have circuitry to measure RMS voltage,
rather than average voltage? I guess so, because that would be crucial
to end up with a correct result. The point here is that the only
reasonable way to add up harmonics is to add their powers. That is why
the *RMS* voltage of the (sum of all) harmonics would have to be
measured.

In the standard distortion analyzers, like the HP 339, Soundtech 1700,
etc., they either use a rms circuit or an average detector to measure

^^^^^^^ Really???

Was there a question?


(a) the level of the signal under test, and (b) the level of that signal
after the fundamental has been nulled out. No one uses a power sensor to
measure distortion or signal power.

You can also use a spectrum analyzer to measure distortion. In that
case, a narrow-band measurement is made at each harmonic frequency, but
the detector used is still either a rms detector or an average detector.

So, in all cases, you are still measuring voltages, not powers, for the
simple reason that you are supplying a signal in the form of *voltage*.

So let's say that you have only two distorsion products, 2% of second
harmonic and 1% of third harmonic. How much total harmonic distortion
do you have then?

My response would be sqrt(0.02^2+0.01^2)=0.022 or 2.2%. The equation
can be seen as "calulate the powers, add them up, and convert back to
voltage".
An RMS measurement of the residual voltage would yield this value, but
if an analyser would measure AVERAGE (absolute) voltage of the
residual, the result would come out wrong, right?

An average detector rectifies the signal and takes the average. It does
not provide the same result as an rms detector, and a fudge factor is
added to make the numbers agree for sinusiodal signals. But the
difference is small. RMS detectors are the correct detector to use, but
they are more expensive. There is yet another detector, the peak
detector, that can be used, but it would give an even larger error
compared to the rms detector.

As an aside, my first job was designing a distortion analyzer many years
ago.


And, in some sense, by measuring RMS voltage the power is involved.
Not directly though, of course.

There exist some signals with certain crest factors that give
significantly different results whether you use an average detector or
rms detector. I'll leave that as an exercise to you.

Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

(Dick Pierce) wrote in message . com...
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante)
wrote:

Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the
VOLTAGES that are compared (in the electrical case) not the POWERS. So
if we have a second harmonic 40 dB down, the second harmonic
distorsion is 1 %, not 0.01 %.
(In this case the voltage of the harmonic is 1% of the fundamental,
and its power is 0.01% of the fundamental)

What is the reason for this convention? I'd think that power would be
more logical.

---
It is _much_ easier to notch out the fundamental(s) and measure the
voltage of the remaining component(s) than it is to measure their power.

Then, knowing the voltage of the offending component(s) appearing across
the load and the impedance of the load at the various frequencies at
which distortion rears its ugly head, their contribution to the power
being dissipated in/by the load can be easily calculated.

Precisely. ALL of the THD meters in existance are essentially
voltmeters with filters. Going from the ancient and venerable
General Radio 1936 or Hewlett-Packard 330, through the HP 334,
through the Sound Technology 1700, Amber, Marconi and so on,
they are ALL voltmeters that have a narrow-band notch filter
in them.

Hmm, just curious, did they have circuitry to measure RMS voltage,
rather than average voltage? I guess so, because that would be crucial
to end up with a correct result. The point here is that the only
reasonable way to add up harmonics is to add their powers. That is why
the *RMS* voltage of the (sum of all) harmonics would have to be
measured.

In the standard distortion analyzers, like the HP 339, Soundtech 1700,
etc., they either use a rms circuit or an average detector to measure

^^^^^^^ Really???

Was there a question?


(a) the level of the signal under test, and (b) the level of that signal
after the fundamental has been nulled out. No one uses a power sensor to
measure distortion or signal power.

You can also use a spectrum analyzer to measure distortion. In that
case, a narrow-band measurement is made at each harmonic frequency, but
the detector used is still either a rms detector or an average detector.

So, in all cases, you are still measuring voltages, not powers, for the
simple reason that you are supplying a signal in the form of *voltage*.

So let's say that you have only two distorsion products, 2% of second
harmonic and 1% of third harmonic. How much total harmonic distortion
do you have then?

My response would be sqrt(0.02^2+0.01^2)=0.022 or 2.2%. The equation
can be seen as "calulate the powers, add them up, and convert back to
voltage".
An RMS measurement of the residual voltage would yield this value, but
if an analyser would measure AVERAGE (absolute) voltage of the
residual, the result would come out wrong, right?

An average detector rectifies the signal and takes the average. It does
not provide the same result as an rms detector, and a fudge factor is
added to make the numbers agree for sinusiodal signals. But the
difference is small. RMS detectors are the correct detector to use, but
they are more expensive. There is yet another detector, the peak
detector, that can be used, but it would give an even larger error
compared to the rms detector.

As an aside, my first job was designing a distortion analyzer many years
ago.


And, in some sense, by measuring RMS voltage the power is involved.
Not directly though, of course.

There exist some signals with certain crest factors that give
significantly different results whether you use an average detector or
rms detector. I'll leave that as an exercise to you.

Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

(Dick Pierce) wrote in message . com...
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante)
wrote:

Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the
VOLTAGES that are compared (in the electrical case) not the POWERS. So
if we have a second harmonic 40 dB down, the second harmonic
distorsion is 1 %, not 0.01 %.
(In this case the voltage of the harmonic is 1% of the fundamental,
and its power is 0.01% of the fundamental)

What is the reason for this convention? I'd think that power would be
more logical.

---
It is _much_ easier to notch out the fundamental(s) and measure the
voltage of the remaining component(s) than it is to measure their power.

Then, knowing the voltage of the offending component(s) appearing across
the load and the impedance of the load at the various frequencies at
which distortion rears its ugly head, their contribution to the power
being dissipated in/by the load can be easily calculated.

Precisely. ALL of the THD meters in existance are essentially
voltmeters with filters. Going from the ancient and venerable
General Radio 1936 or Hewlett-Packard 330, through the HP 334,
through the Sound Technology 1700, Amber, Marconi and so on,
they are ALL voltmeters that have a narrow-band notch filter
in them.

Hmm, just curious, did they have circuitry to measure RMS voltage,
rather than average voltage? I guess so, because that would be crucial
to end up with a correct result. The point here is that the only
reasonable way to add up harmonics is to add their powers. That is why
the *RMS* voltage of the (sum of all) harmonics would have to be
measured.

In the standard distortion analyzers, like the HP 339, Soundtech 1700,
etc., they either use a rms circuit or an average detector to measure

^^^^^^^ Really???

Was there a question?


(a) the level of the signal under test, and (b) the level of that signal
after the fundamental has been nulled out. No one uses a power sensor to
measure distortion or signal power.

You can also use a spectrum analyzer to measure distortion. In that
case, a narrow-band measurement is made at each harmonic frequency, but
the detector used is still either a rms detector or an average detector.

So, in all cases, you are still measuring voltages, not powers, for the
simple reason that you are supplying a signal in the form of *voltage*.

So let's say that you have only two distorsion products, 2% of second
harmonic and 1% of third harmonic. How much total harmonic distortion
do you have then?

My response would be sqrt(0.02^2+0.01^2)=0.022 or 2.2%. The equation
can be seen as "calulate the powers, add them up, and convert back to
voltage".
An RMS measurement of the residual voltage would yield this value, but
if an analyser would measure AVERAGE (absolute) voltage of the
residual, the result would come out wrong, right?

An average detector rectifies the signal and takes the average. It does
not provide the same result as an rms detector, and a fudge factor is
added to make the numbers agree for sinusiodal signals. But the
difference is small. RMS detectors are the correct detector to use, but
they are more expensive. There is yet another detector, the peak
detector, that can be used, but it would give an even larger error
compared to the rms detector.

As an aside, my first job was designing a distortion analyzer many years
ago.


And, in some sense, by measuring RMS voltage the power is involved.
Not directly though, of course.

There exist some signals with certain crest factors that give
significantly different results whether you use an average detector or
rms detector. I'll leave that as an exercise to you.

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

Svante wrote:
chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

You need to read more EE textbooks

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

You missed what I wrote: to keep it consistent with power ratios
expressed in dB's. So that a dB is a dB!

Svante wrote:
chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

You need to read more EE textbooks

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

You missed what I wrote: to keep it consistent with power ratios
expressed in dB's. So that a dB is a dB!

Svante wrote:
chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

You need to read more EE textbooks

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

You missed what I wrote: to keep it consistent with power ratios
expressed in dB's. So that a dB is a dB!

Svante wrote:
chung wrote in message ervers.com...
Svante wrote:
chung wrote in message rvers.com...
Svante wrote:

chung wrote in message ervers.com...
Svante wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No such assumption.

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance.

It is a definition, not a derivation.

So, if it is a definition, free from association with the power ratio,
why does it say "20" times the logarith of the ratio. deci would mean
ten (or a tenth).

It's defined in such a way so that voltage ratios in dB is consistent
with power ratios in dB.

Read any textbook. dB is always defined, not derived.

I have read not just any, but many textbooks. And yes, dB is defined,
but only once. That definition is

dB = 10 * log (p/pref)

You need to read more EE textbooks

From that we can DERIVE, given a constant load resistance and that
p=u^2/R, that

dB = 10 * log (u^2 / uref^2) = 20 * log (u/uref)

Am I the only one that sees the power ratio as the logical way to
define the dB. I mean, I know that deci stands for a tenth, WHY ON
EARTH would we put TWENTY in the equation if we defined dBs based on a
voltage ratio????

You missed what I wrote: to keep it consistent with power ratios
expressed in dB's. So that a dB is a dB!

(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

On Sun, 18 Jan 2004 08:15:09 -0600, John Fields
- The wave analyser approach whereby distortion products are discretely and
separately measured. This I remember as being the older method. A person then
calculated distortion by a formula which (correct me if wrong) was along the
lines of ...

1 / square root of the sum of the individual voltages (squared).
There was a variant of this formula but others can quibble if need be.


I believe it would have been the square root of the sum of the squares
of the individual voltages (the 'RMS', or Root Mean Square), not its
reciprocal, which would have been used in the calculation.


Actually John, I made a fairly serious error there.
I realised it as soon as committing it to the outside world (that's life)
It's really ...
Sqrt ( sum of components squared) / Fundamental value
Where Fundamental = primary component (usually 1 or 'normalised' at 100%)
This implies that the dist. products are ' fractionalised'.
Anyway, you get the picture -)

On Sun, 18 Jan 2004 08:15:09 -0600, John Fields
- The wave analyser approach whereby distortion products are discretely and
separately measured. This I remember as being the older method. A person then
calculated distortion by a formula which (correct me if wrong) was along the
lines of ...

1 / square root of the sum of the individual voltages (squared).
There was a variant of this formula but others can quibble if need be.


I believe it would have been the square root of the sum of the squares
of the individual voltages (the 'RMS', or Root Mean Square), not its
reciprocal, which would have been used in the calculation.


Actually John, I made a fairly serious error there.
I realised it as soon as committing it to the outside world (that's life)
It's really ...
Sqrt ( sum of components squared) / Fundamental value
Where Fundamental = primary component (usually 1 or 'normalised' at 100%)
This implies that the dist. products are ' fractionalised'.
Anyway, you get the picture -)

On Sun, 18 Jan 2004 08:15:09 -0600, John Fields
- The wave analyser approach whereby distortion products are discretely and
separately measured. This I remember as being the older method. A person then
calculated distortion by a formula which (correct me if wrong) was along the
lines of ...

1 / square root of the sum of the individual voltages (squared).
There was a variant of this formula but others can quibble if need be.


I believe it would have been the square root of the sum of the squares
of the individual voltages (the 'RMS', or Root Mean Square), not its
reciprocal, which would have been used in the calculation.


Actually John, I made a fairly serious error there.
I realised it as soon as committing it to the outside world (that's life)
It's really ...
Sqrt ( sum of components squared) / Fundamental value
Where Fundamental = primary component (usually 1 or 'normalised' at 100%)
This implies that the dist. products are ' fractionalised'.
Anyway, you get the picture -)

On Sun, 18 Jan 2004 08:15:09 -0600, John Fields
- The wave analyser approach whereby distortion products are discretely and
separately measured. This I remember as being the older method. A person then
calculated distortion by a formula which (correct me if wrong) was along the
lines of ...

1 / square root of the sum of the individual voltages (squared).
There was a variant of this formula but others can quibble if need be.


I believe it would have been the square root of the sum of the squares
of the individual voltages (the 'RMS', or Root Mean Square), not its
reciprocal, which would have been used in the calculation.


Actually John, I made a fairly serious error there.
I realised it as soon as committing it to the outside world (that's life)
It's really ...
Sqrt ( sum of components squared) / Fundamental value
Where Fundamental = primary component (usually 1 or 'normalised' at 100%)
This implies that the dist. products are ' fractionalised'.
Anyway, you get the picture -)

On Sun, 18 Jan 2004 15:46:43 +0000 (UTC), (Stewart
Pinkerton) wrote:

- The nulling of the fundamental and then measuring the rest of the garbage.
This also included a noise component which might (not) be significant.
It is, (here I don a flame suit at this moment), the more common way.
Quite often a HP machine (334) is a typical device for this work

That's why the proper term is THD+N.

Precisely. But the point needs to be made.
Some people forget the fact

This "voltage" approach is probably (well, I would contend that it is) the
single most important influence on the definition and approach to
measuring (and defining) distortion. All of this is predicated on the purity
of the original signal source (sine) which, in itself, is a separate subject

No, the fundamental is *by definition* a sine wave. If you are
measuring the distortion of an amplifier, you certainly want a pure
sinusioidal source, but that's not exactly rocket science!

Your precision is correct.
It was a throwaway line for people who might not have
realised the 'problem' inherent in simple measurements.

On Sun, 18 Jan 2004 15:46:43 +0000 (UTC), (Stewart
Pinkerton) wrote:

- The nulling of the fundamental and then measuring the rest of the garbage.
This also included a noise component which might (not) be significant.
It is, (here I don a flame suit at this moment), the more common way.
Quite often a HP machine (334) is a typical device for this work

That's why the proper term is THD+N.

Precisely. But the point needs to be made.
Some people forget the fact

This "voltage" approach is probably (well, I would contend that it is) the
single most important influence on the definition and approach to
measuring (and defining) distortion. All of this is predicated on the purity
of the original signal source (sine) which, in itself, is a separate subject

No, the fundamental is *by definition* a sine wave. If you are
measuring the distortion of an amplifier, you certainly want a pure
sinusioidal source, but that's not exactly rocket science!

Your precision is correct.
It was a throwaway line for people who might not have
realised the 'problem' inherent in simple measurements.

On Sun, 18 Jan 2004 15:46:43 +0000 (UTC), (Stewart
Pinkerton) wrote:

- The nulling of the fundamental and then measuring the rest of the garbage.
This also included a noise component which might (not) be significant.
It is, (here I don a flame suit at this moment), the more common way.
Quite often a HP machine (334) is a typical device for this work

That's why the proper term is THD+N.

Precisely. But the point needs to be made.
Some people forget the fact

This "voltage" approach is probably (well, I would contend that it is) the
single most important influence on the definition and approach to
measuring (and defining) distortion. All of this is predicated on the purity
of the original signal source (sine) which, in itself, is a separate subject

No, the fundamental is *by definition* a sine wave. If you are
measuring the distortion of an amplifier, you certainly want a pure
sinusioidal source, but that's not exactly rocket science!

Your precision is correct.
It was a throwaway line for people who might not have
realised the 'problem' inherent in simple measurements.

On Sun, 18 Jan 2004 15:46:43 +0000 (UTC), (Stewart
Pinkerton) wrote:

- The nulling of the fundamental and then measuring the rest of the garbage.
This also included a noise component which might (not) be significant.
It is, (here I don a flame suit at this moment), the more common way.
Quite often a HP machine (334) is a typical device for this work

That's why the proper term is THD+N.

Precisely. But the point needs to be made.
Some people forget the fact

This "voltage" approach is probably (well, I would contend that it is) the
single most important influence on the definition and approach to
measuring (and defining) distortion. All of this is predicated on the purity
of the original signal source (sine) which, in itself, is a separate subject

No, the fundamental is *by definition* a sine wave. If you are
measuring the distortion of an amplifier, you certainly want a pure
sinusioidal source, but that's not exactly rocket science!

Your precision is correct.
It was a throwaway line for people who might not have
realised the 'problem' inherent in simple measurements.

(Dick Pierce) wrote in message . com...
(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

Nope. 10^-12 watt/m^2 would be 0 dB SIL, or sound intensity level. It
would be APPROXIMATELY 0 dB SPL too, but that would rely on normal
conditions (temp, pressure etc). 0 dB SPL is 2*10^-5 Pa.

(Dick Pierce) wrote in message . com...
(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

Nope. 10^-12 watt/m^2 would be 0 dB SIL, or sound intensity level. It
would be APPROXIMATELY 0 dB SPL too, but that would rely on normal
conditions (temp, pressure etc). 0 dB SPL is 2*10^-5 Pa.

(Dick Pierce) wrote in message . com...
(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

Nope. 10^-12 watt/m^2 would be 0 dB SIL, or sound intensity level. It
would be APPROXIMATELY 0 dB SPL too, but that would rely on normal
conditions (temp, pressure etc). 0 dB SPL is 2*10^-5 Pa.

(Dick Pierce) wrote in message . com...
(Stewart Pinkerton) wrote in message ...
On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:
I mean, the fundaments of dB
assumes that we measure a power ratio.

No, it doesn't. It is simply a useful logarithmic ratio.

I can't bring to mind any meaningful use of the decibel that is not
derived from power measurements, including dBSPL.

SPL is a pressure level, not anything to do with power per se.

Well, no. 0 dB SPL is defined as 0.0002 dyne/cm^2, which is
also 10^-12 watt/m^2.

Nope. 10^-12 watt/m^2 would be 0 dB SIL, or sound intensity level. It
would be APPROXIMATELY 0 dB SPL too, but that would rely on normal
conditions (temp, pressure etc). 0 dB SPL is 2*10^-5 Pa.

On Mon, 19 Jan 2004 02:21:31 GMT, (John Fields)
wrote:

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

e, them were't days, lad........................ :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Mon, 19 Jan 2004 02:21:31 GMT, (John Fields)
wrote:

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

e, them were't days, lad........................ :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Mon, 19 Jan 2004 02:21:31 GMT, (John Fields)
wrote:

On 18 Jan 2004 14:54:25 -0800, (Svante)
wrote:

Glenn Booth wrote in message ...
Hi,

In message , Stewart Pinkerton
writes

I am a Scot, but I'm 56 years old, and I was brought up with feet and
inches, and with pounds, shillings and pence. Yes, the metric system
is simpler, but this doesn't affect how we *think*. I am 6 feet 3
inches tall, I know how tall is someone who is 6 feet tall, but I have
no idea how tall is someone who is 1.83 metres tall.................

I'm similar, but not a Scot :-)

We bought new weighing scales that only work in kilos, and I'm tempted
to throw them at the wall. I can only think in stones, despite knowing
the conversion factor very well. I think I'll be that way until I die.

It makes me laugh when the large print on milk bottles says "1.136
litres", with "2 pints" written underneath in a minuscule typeface. It's
so obviously designed for people who think in imperial measures, but the
law says it has to be sold in metric.

Slightly more on topic, I understand there is a move afoot to replace
the decibel with the 'neper' (an SI unit). I hope it doesn't catch on;
I'm only just beginning to get a proper understanding of the old system.

I have hesitated to bring the Neper into this discussion, but as you
do I'll bring the following up:

While the dB is fundamentally defined as describing a POWER (or
intensity)ratio, the neper is defined as describing a VOLTAGE (or
pressure/velocity/current) ratio. Further more, it uses the natural
logarithm. So, while the dB is defined in it most pure :-) form as

dB = 10 * log10 (p/pref)

the Neper is defined as:

Np = ln (U/Uref)

On the page http://physics.nist.gov/cuu/Units/outside.html
, however, both dB and Np are listed as being "outside" the metric
system, but accepted for use with tha metric system.

I also hope that the neper never will be a success. Possibly this has
to do with me having ten fingers, rather than 2.71.

---
The neper is already a success, and has been used for years and years
in telecommunications. For a quick peek,

http://www.sizes.com/units/neper.htm

Possibly the reason you'd like for it not to have become a success is
because you're already having a lot of trouble sorting out n(dB) = 20
log10 from n(dB) = 10 log10, and being confronted with having to sort
out n(Np) = logn A/Aref from n(Np) = 0.5 logn P/Pref is 2.713...
times more daunting?^)

e, them were't days, lad........................ :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering