Noise Weighting Curves
 

Don Pearce wrote:

OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear.

Yes, well Dolby had an interest in it didn't they ?

Graham

Noise Weighting Curves
 

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
ahti.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superceded "A" curve.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.

d

Bugger, that is 9dB, not 19.

d

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

Noise Weighting Curves
 

On Thu, 04 Oct 2007 09:49:25 +0100, Eeyore
wrote:



Don Pearce wrote:

OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear.

Yes, well Dolby had an interest in it didn't they ?

Graham

Now *that* is cynical! Why didn't I think of it?

d

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

Noise Weighting Curves
 

"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superceded "A" curve.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

Noise Weighting Curves
 

On Thu, 4 Oct 2007 13:05:30 +0300, "Iain Churches"
wrote:

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

Such a difference would suggest a great deal of 1/f noise.

d

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

Noise Weighting Curves
 

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 13:05:30 +0300, "Iain Churches"
wrote:

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

Such a difference would suggest a great deal of 1/f noise.

Indeed, and of course noise beyond the top end of
the audio band.

The amp that I mentioned had 100Hz audible
from the listening position The owner said
"All tube amps hum like that!"

"Ahaa!", sez I.

Iain

Noise Weighting Curves
 

In article ,
Don Pearce wrote:
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

Such a difference would suggest a great deal of 1/f noise.

Fairly typical of AF valve circuits. Hum.

--
*Ever stop to think and forget to start again?

Dave Plowman London SW
To e-mail, change noise into sound.

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article ,
Don Pearce wrote:
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

Such a difference would suggest a great deal of 1/f noise.

Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

http://www.kolumbus.fi/iain.churches...em/C50_002.jpg

Iain

Noise Weighting Curves
 

On Thu, 4 Oct 2007 18:51:36 +0300, "Iain Churches"
wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Don Pearce wrote:
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

Such a difference would suggest a great deal of 1/f noise.

Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

http://www.kolumbus.fi/iain.churches...em/C50_002.jpg

Iain

Not a misconception, Dave is right - yours is hardly a typical valve
amp. My impression of the huge majority of the valve amps I have come
across is that you just know when they are switched on; there is
always that "liveness" about the speakers, usually a mixture of hum
and noise.

d

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

Noise Weighting Curves
 

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 18:51:36 +0300, "Iain Churches"
wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Don Pearce wrote:
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

Such a difference would suggest a great deal of 1/f noise.

Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

http://www.kolumbus.fi/iain.churches...em/C50_002.jpg


Not a misconception, Dave is right - yours is hardly a typical valve
amp. My impression of the huge majority of the valve amps I have come
across is that you just know when they are switched on; there is
always that "liveness" about the speakers, usually a mixture of hum
and noise.

Of the thirty or so members of the "gramophone society" to which
I belong, more than half have valve amps. I cannot think of a
single member who has a system where one can even hear a
hint of hum/hiss at the listening position. Most systems are
silent with ear against speaker.

With the exception of the Cheepies, the quality of valve amps
offered by the many bespoke builders is very high indeed.
I would say the performance of my own is typical.

Iain