"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