[Iain Churches[_2_]]

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

[Eeyore]

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:-)

Yes, it allows indifferent performance to be dressed up as looking rather
better. That's the only real reason for its existence.

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


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:-)

Yes, it allows indifferent performance to be dressed up as looking rather
better. That's the only real reason for its existence.

It exists because, at the time of its introduction, it was believed to
be an accurate representation of the ear's response. It later became
apparent that the curve required for evaluation of the loudness of
tones was different to that required for the evaluation of noise.

I was looking at the performance of a British tube amp yesterday.
The difference in the noise floor measured audio band, and then
measured "A" weighted, was 20dB !!

It looks as though the Dolby proposal for ITU-ARM was not
adopted as the curve is not shifted upwards by 1kHz, but there is
a level offset of 5.6dB.

Regards
Iain

[Eeyore]

Iain Churches wrote:

I was looking at the performance of a British tube amp yesterday.
The difference in the noise floor measured audio band, and then
measured "A" weighted, was 20dB !!

Maybe it had very bad hum ? A weighting would be 'kind' to that.and is a perfect
example of how flawed an idea it is since a discrete frequency (and related
harmonics) such as hum is far more intrusive than wideband noise.


It looks as though the Dolby proposal for ITU-ARM was not
adopted as the curve is not shifted upwards by 1kHz, but there is
a level offset of 5.6dB.

It's another 'cheat'. IIRC the idea was to have a reference at 2kHz rather than
1 kHz but basically they just ended up lopping almost 6 dB off the A wtd
numbers. A ridiculous idea except for those who like to cheat.

Graham

[Iain Churches[_2_]]

"Eeyore" wrote in message
...


Iain Churches wrote:

I was looking at the performance of a British tube amp yesterday.
The difference in the noise floor measured audio band, and then
measured "A" weighted, was 20dB !!

Maybe it had very bad hum ? A weighting would be 'kind' to that.and is a
perfect
example of how flawed an idea it is since a discrete frequency (and
related
harmonics) such as hum is far more intrusive than wideband noise.

A cigar for that man!

It had the simplest of psu's - Just one large reservoir cap
for each side, no choke, and only minimal decoupling.
The hum was audible with no signal from the listening position.
The owner said, "All tube amps hum like that!"

It looks as though the Dolby proposal for ITU-ARM was not
adopted as the curve is not shifted upwards by 1kHz, but there is
a level offset of 5.6dB.

It's another 'cheat'. IIRC the idea was to have a reference at 2kHz rather
than 1 kHz but basically they just ended up lopping almost 6 dB off the A
wtd
numbers. A ridiculous idea except for those who like to cheat.

The info I have was that the Dolby proposal for ARM was that the
peak should be shifted 1kHz higher at 7.2kHz otherwise the curve was
to remain the same.

The old "A" weighted curve peaked at 2462-2549Hz
and was often known as the 2k5 curve.


Iain