"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