"Don Pearce" wrote in message
...
On Thu, 04 Oct 2007 08:48:33 GMT, (Don Pearce)
wrote:

On Thu, 4 Oct 2007 11:38:01 +0300, "Iain Churches"
wrote:


"Iain Churches" wrote in message
lahti.fi...

Which explains why many still stubbornly use the long
superceded "A" curve.


Don. I forgot to mention, I was looking at a British valve amp
yesterday built 1990s. The difference between the noise
floor measured "audio band" and "A" weighted was 20dB !!

A magical improvement at the press of a button.

Iain


Just done something similar on my DAW. I've also created an A curve.
Made a chunk of white noise and compared the average noise levels.

Flat -19.44dB
A wt -21.7dB
468 -12.59dB

So that is a 19dB difference. I only eyeballed the filters, so I could
be a bit out. This is all a bit odd. I can see there being differences
between two subjective curves purporting to be of the same thing, but
19dB? Something smells nasty.

"A" and 468 do not purport to be the same thing. The latter
was introduced specifically to correct the apparent errors in
the former.

Bugger, that is 9dB, not 19.

The pong is alleviated by 10dB:-)

In tube power amps, the difference between wide
band and "A" weighted was often found to be 12dB,
and this was, IIRC something of a rule of thumb.

Iain