John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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

- 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.

Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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
-)

.... Stands back .... prepares grapeshot to repel the oncoming attack ...

On Sat, 17 Jan 2004 11:51:37 +0000 (UTC), (Stewart
Pinkerton) wrote:

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

While I _WILL NOT_ be contending, or entering into the digressed subject
thread, I find that I must, at least offer an alternative viewpoint to your
statement above.

If a sound (note that) is suddenly increased in magnitude, the listener
receives an impression of increased loudness which is roughly (note that)
proportional to the logarithm of the ratio of the two acoustical powers. i.e.
loudness is proportional to log(P1/P2).

From that definition, it follows that power (and practically everything else)
can be measured (described comparatively).
I would _not_ think that it is a measure of SPL (at least, not in an absolute
baseline sense). Maybe I'm misinterpreting you (I hope not).

This is also the definition of the BEL (of course)

On Sat, 17 Jan 2004 11:51:37 +0000 (UTC), (Stewart
Pinkerton) wrote:

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

While I _WILL NOT_ be contending, or entering into the digressed subject
thread, I find that I must, at least offer an alternative viewpoint to your
statement above.

If a sound (note that) is suddenly increased in magnitude, the listener
receives an impression of increased loudness which is roughly (note that)
proportional to the logarithm of the ratio of the two acoustical powers. i.e.
loudness is proportional to log(P1/P2).

From that definition, it follows that power (and practically everything else)
can be measured (described comparatively).
I would _not_ think that it is a measure of SPL (at least, not in an absolute
baseline sense). Maybe I'm misinterpreting you (I hope not).

This is also the definition of the BEL (of course)

On Sat, 17 Jan 2004 11:51:37 +0000 (UTC), (Stewart
Pinkerton) wrote:

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

While I _WILL NOT_ be contending, or entering into the digressed subject
thread, I find that I must, at least offer an alternative viewpoint to your
statement above.

If a sound (note that) is suddenly increased in magnitude, the listener
receives an impression of increased loudness which is roughly (note that)
proportional to the logarithm of the ratio of the two acoustical powers. i.e.
loudness is proportional to log(P1/P2).

From that definition, it follows that power (and practically everything else)
can be measured (described comparatively).
I would _not_ think that it is a measure of SPL (at least, not in an absolute
baseline sense). Maybe I'm misinterpreting you (I hope not).

This is also the definition of the BEL (of course)

On Sat, 17 Jan 2004 11:51:37 +0000 (UTC), (Stewart
Pinkerton) wrote:

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

While I _WILL NOT_ be contending, or entering into the digressed subject
thread, I find that I must, at least offer an alternative viewpoint to your
statement above.

If a sound (note that) is suddenly increased in magnitude, the listener
receives an impression of increased loudness which is roughly (note that)
proportional to the logarithm of the ratio of the two acoustical powers. i.e.
loudness is proportional to log(P1/P2).

From that definition, it follows that power (and practically everything else)
can be measured (described comparatively).
I would _not_ think that it is a measure of SPL (at least, not in an absolute
baseline sense). Maybe I'm misinterpreting you (I hope not).

This is also the definition of the BEL (of course)

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).

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).

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).

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).

John Fields wrote in message . ..
For example, 0dBm (not 0dB(m)) identifies the reference level as being
one milliwatt.

I guess that 0 dB(m) would be one meter then... ;-)

John Fields wrote in message . ..
For example, 0dBm (not 0dB(m)) identifies the reference level as being
one milliwatt.

I guess that 0 dB(m) would be one meter then... ;-)

John Fields wrote in message . ..
For example, 0dBm (not 0dB(m)) identifies the reference level as being
one milliwatt.

I guess that 0 dB(m) would be one meter then... ;-)

John Fields wrote in message . ..
For example, 0dBm (not 0dB(m)) identifies the reference level as being
one milliwatt.

I guess that 0 dB(m) would be one meter then... ;-)

On 18 Jan 2004 02:49:39 -0800, (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).

---
The original unit was the BEL, but it proved to be too large for
convenient use so it was divided by 10 to yield the deci-BEL, now noted
as the 'dB', so what dB = 20 log (V/Vref) is saying is that 20 times
the log of the voltage (or current) ratio is equal to one deci-BEL.

--
John Fields

On 18 Jan 2004 02:49:39 -0800, (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).

---
The original unit was the BEL, but it proved to be too large for
convenient use so it was divided by 10 to yield the deci-BEL, now noted
as the 'dB', so what dB = 20 log (V/Vref) is saying is that 20 times
the log of the voltage (or current) ratio is equal to one deci-BEL.

--
John Fields

On 18 Jan 2004 02:49:39 -0800, (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).

---
The original unit was the BEL, but it proved to be too large for
convenient use so it was divided by 10 to yield the deci-BEL, now noted
as the 'dB', so what dB = 20 log (V/Vref) is saying is that 20 times
the log of the voltage (or current) ratio is equal to one deci-BEL.

--
John Fields

On 18 Jan 2004 02:49:39 -0800, (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).

---
The original unit was the BEL, but it proved to be too large for
convenient use so it was divided by 10 to yield the deci-BEL, now noted
as the 'dB', so what dB = 20 log (V/Vref) is saying is that 20 times
the log of the voltage (or current) ratio is equal to one deci-BEL.

--
John Fields

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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

- 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.
---


Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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

---
Indeed.

Assuming a perfectly linear amplifier and perfect nulling of the
source's fundamental at the amp's putput, the remaining distortion
products would be the source's, not the amp's.

--
John Fields

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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

- 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.
---


Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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

---
Indeed.

Assuming a perfectly linear amplifier and perfect nulling of the
source's fundamental at the amp's putput, the remaining distortion
products would be the source's, not the amp's.

--
John Fields

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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

- 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.
---


Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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

---
Indeed.

Assuming a perfectly linear amplifier and perfect nulling of the
source's fundamental at the amp's putput, the remaining distortion
products would be the source's, not the amp's.

--
John Fields

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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

- 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.
---


Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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

---
Indeed.

Assuming a perfectly linear amplifier and perfect nulling of the
source's fundamental at the amp's putput, the remaining distortion
products would be the source's, not the amp's.

--
John Fields

On 17 Jan 2004 08:46:44 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...

But yes, I still *think* in feet, not metres................

Should I say that I'm a Swede, if you wonder. I was raised with the
metric system, and appreciate it a lot and cannot understand how feet
could possibly be more intuitive than metres. Heck, even our mile is
metric (10 000 metres).
I can't help quoting my mechanics teacher who was a member of the
swedish standards committe: "England is going metric, inch by inch..."

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.................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:46:44 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...

But yes, I still *think* in feet, not metres................

Should I say that I'm a Swede, if you wonder. I was raised with the
metric system, and appreciate it a lot and cannot understand how feet
could possibly be more intuitive than metres. Heck, even our mile is
metric (10 000 metres).
I can't help quoting my mechanics teacher who was a member of the
swedish standards committe: "England is going metric, inch by inch..."

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.................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:46:44 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...

But yes, I still *think* in feet, not metres................

Should I say that I'm a Swede, if you wonder. I was raised with the
metric system, and appreciate it a lot and cannot understand how feet
could possibly be more intuitive than metres. Heck, even our mile is
metric (10 000 metres).
I can't help quoting my mechanics teacher who was a member of the
swedish standards committe: "England is going metric, inch by inch..."

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.................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:46:44 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...

But yes, I still *think* in feet, not metres................

Should I say that I'm a Swede, if you wonder. I was raised with the
metric system, and appreciate it a lot and cannot understand how feet
could possibly be more intuitive than metres. Heck, even our mile is
metric (10 000 metres).
I can't help quoting my mechanics teacher who was a member of the
swedish standards committe: "England is going metric, inch by inch..."

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.................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:

Hi,

In message , Stewart Pinkerton
writes
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

I won't attempt to refute this statement, but I was under the impression
that the decibel (or rather, the Bel) was originally created in order to
simplify the calculation of relative electrical power levels in
telecommunication circuits. I think I read such in the Yamaha Sound
Reinforcement Handbook. Since I have no idea how accurate that source
is, I would be interested in finding out the real history.

The Bel was first used as an indicator of relative loudness, being the
ratio of SPLs necessary for one sound to be perceived as being twice
as loud as another. It is named after Alexander Graham Bell, who was
principally an audiologist.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:

Hi,

In message , Stewart Pinkerton
writes
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

I won't attempt to refute this statement, but I was under the impression
that the decibel (or rather, the Bel) was originally created in order to
simplify the calculation of relative electrical power levels in
telecommunication circuits. I think I read such in the Yamaha Sound
Reinforcement Handbook. Since I have no idea how accurate that source
is, I would be interested in finding out the real history.

The Bel was first used as an indicator of relative loudness, being the
ratio of SPLs necessary for one sound to be perceived as being twice
as loud as another. It is named after Alexander Graham Bell, who was
principally an audiologist.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:

Hi,

In message , Stewart Pinkerton
writes
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

I won't attempt to refute this statement, but I was under the impression
that the decibel (or rather, the Bel) was originally created in order to
simplify the calculation of relative electrical power levels in
telecommunication circuits. I think I read such in the Yamaha Sound
Reinforcement Handbook. Since I have no idea how accurate that source
is, I would be interested in finding out the real history.

The Bel was first used as an indicator of relative loudness, being the
ratio of SPLs necessary for one sound to be perceived as being twice
as loud as another. It is named after Alexander Graham Bell, who was
principally an audiologist.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 22:53:10 +0000, Glenn Booth
wrote:

Hi,

In message , Stewart Pinkerton
writes
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

I won't attempt to refute this statement, but I was under the impression
that the decibel (or rather, the Bel) was originally created in order to
simplify the calculation of relative electrical power levels in
telecommunication circuits. I think I read such in the Yamaha Sound
Reinforcement Handbook. Since I have no idea how accurate that source
is, I would be interested in finding out the real history.

The Bel was first used as an indicator of relative loudness, being the
ratio of SPLs necessary for one sound to be perceived as being twice
as loud as another. It is named after Alexander Graham Bell, who was
principally an audiologist.

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.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 09:25:45 -0600, John Fields
wrote:

Now, since water is/was ubiquitous on the surface of the earth and,
presumably, weighed the same everywhere, it was decided that a certain
volume of water (the 'cubic centimeter', a cube one centimeter on an
edge) would become the standard of weight and was called the 'gramme'.

The prefix 'kilo', indicating that a multiplication of the quantity
following it by 1000 is required, means "1000 grams" when appended with
'gram'. Hence, kilo+gram = kilogram = 1000 * 1 gram = 1000 grams.

Since this appears to be descending into pedantry, I should note that
the gram is certainly *not* a unit of weight, but of mass.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 09:25:45 -0600, John Fields
wrote:

Now, since water is/was ubiquitous on the surface of the earth and,
presumably, weighed the same everywhere, it was decided that a certain
volume of water (the 'cubic centimeter', a cube one centimeter on an
edge) would become the standard of weight and was called the 'gramme'.

The prefix 'kilo', indicating that a multiplication of the quantity
following it by 1000 is required, means "1000 grams" when appended with
'gram'. Hence, kilo+gram = kilogram = 1000 * 1 gram = 1000 grams.

Since this appears to be descending into pedantry, I should note that
the gram is certainly *not* a unit of weight, but of mass.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 09:25:45 -0600, John Fields
wrote:

Now, since water is/was ubiquitous on the surface of the earth and,
presumably, weighed the same everywhere, it was decided that a certain
volume of water (the 'cubic centimeter', a cube one centimeter on an
edge) would become the standard of weight and was called the 'gramme'.

The prefix 'kilo', indicating that a multiplication of the quantity
following it by 1000 is required, means "1000 grams" when appended with
'gram'. Hence, kilo+gram = kilogram = 1000 * 1 gram = 1000 grams.

Since this appears to be descending into pedantry, I should note that
the gram is certainly *not* a unit of weight, but of mass.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 17 Jan 2004 09:25:45 -0600, John Fields
wrote:

Now, since water is/was ubiquitous on the surface of the earth and,
presumably, weighed the same everywhere, it was decided that a certain
volume of water (the 'cubic centimeter', a cube one centimeter on an
edge) would become the standard of weight and was called the 'gramme'.

The prefix 'kilo', indicating that a multiplication of the quantity
following it by 1000 is required, means "1000 grams" when appended with
'gram'. Hence, kilo+gram = kilogram = 1000 * 1 gram = 1000 grams.

Since this appears to be descending into pedantry, I should note that
the gram is certainly *not* a unit of weight, but of mass.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 18 Jan 2004 02:49:39 -0800, (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).

That is irrelevant, since a deciBel is simply one tenth of a Bel, the
original unit which was considered to be excessively large for
everyday use.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 18 Jan 2004 02:49:39 -0800, (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).

That is irrelevant, since a deciBel is simply one tenth of a Bel, the
original unit which was considered to be excessively large for
everyday use.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 18 Jan 2004 02:49:39 -0800, (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).

That is irrelevant, since a deciBel is simply one tenth of a Bel, the
original unit which was considered to be excessively large for
everyday use.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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.

- 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.

Yes, that's right, and PC-based analysers can perform this calculation
automatically.

Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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.

- 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.

Yes, that's right, and PC-based analysers can perform this calculation
automatically.

Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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.

- 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.

Yes, that's right, and PC-based analysers can perform this calculation
automatically.

Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 18 Jan 2004 12:18:14 +1100, Bazza wrote:

John Fields wrote ---
---
When measuring _total_ harmonic distortion, the contribution of each of
the individual partials is immaterial in that what's being determined is
the contribution to distortion that _all_ of the harmonics due to the
fundamental's presence contribute.


Furthermore, even if the contributions of the individual partials were
to be measured, their voltages would each be measured using a tuned
voltmeter and then the process of determining their contribution
determined mathematically. As a matter of fact, in order to measure the
power directly, the normal load would have to be disconnected and a
bolometer with precisely the same impedance as the load substituted for
the load. Expensive and more than just a _bit_ awkward.

You raise a good point John.
I was going to post something to the same effect
which goes to the heart of the original question by Svante

In the 'measurement' of distortion, putting aside the quantitative accuracy
problem for the moment, it was customary for measurements to be done in two
ways.

- 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.

- 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.

Yes, that's right, and PC-based analysers can perform this calculation
automatically.

Of course. If you _missed_ some by-products as the result of 'mixing' i.e. by
assuming only harmonic products, then accuracy suffered, but hey, "the world
ain't poifect anyway". You _could_ , with equal validity, have measured the
products as currents (but voltmeters were more common).

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!
--

Stewart Pinkerton | Music is Art - Audio is Engineering