My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)


Iain

On Thu, 4 Oct 2007 10:00:34 +0300, "Iain Churches"
wrote:

My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)


Iain



Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.

What are the numbers?

d

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

"Don Pearce" wrote in message
...

Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

It looks as if the Dolby recommendation for
the shift upwards of 1kHz was not implemented
I still have a lot of reading to do.

Comparison of noise levels using the different weighting
options is interesting.

Iain

On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...

Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

It looks as if the Dolby recommendation for
the shift upwards of 1kHz was not implemented
I still have a lot of reading to do.

Comparison of noise levels using the different weighting
options is interesting.

Iain


Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

d

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

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:

"Don Pearce" wrote in message
...

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain

On Thu, 4 Oct 2007 11:11:23 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:

"Don Pearce" wrote in message
...

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain



OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear. The numbers won't look
anything like as pretty under CCIR 468.

d

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

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:00:34 +0300, "Iain Churches"
wrote:

My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)


Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.


Don. A bit more news has just filtered in. (Posting on UKRA
often results in informative e.mails from interesting sources)

It seems that the "Dolby shift" for ARM was implemented,
in the sense that 468 crossed 0dB at 1kHz, and ARM crosses
at 2kHz.

468 is intended as a professional standard with ARM a
commercial equivalent.

Best regards
Iain

On Thu, 4 Oct 2007 21:43:04 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:00:34 +0300, "Iain Churches"
wrote:

My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)


Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.


Don. A bit more news has just filtered in. (Posting on UKRA
often results in informative e.mails from interesting sources)

It seems that the "Dolby shift" for ARM was implemented,
in the sense that 468 crossed 0dB at 1kHz, and ARM crosses
at 2kHz.

I think that whoever came up with that bit of back-pedalling must have
been a politician.

d

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

"Iain Churches" wrote in message
ti.fi...
My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)

Do bear in mind what these curves should be approximating. They should be
approximating the appropriate Fletcher-Munson curve for the SPL being
listened to.

On Mon, 15 Oct 2007 08:11:09 -0400, "Arny Krueger"
wrote:


"Iain Churches" wrote in message
hti.fi...
My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)

Do bear in mind what these curves should be approximating. They should be
approximating the appropriate Fletcher-Munson curve for the SPL being
listened to.


Is that true? The F-M curve is for the threshold of audibility and
equivalent loudness for tones on their own at various frequencies. A
noise weighting curve is designed to weight the equivalent
contribution of each frequency to a broad agglomeration. I am not
convinced that these two amount to the same thing.

Do you know of any work that has examined the similarities or
differences between these two?

d

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