Noise Weighting Curves
 

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

Noise Weighting Curves
 

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



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.

What are the numbers?

d

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

Noise Weighting Curves
 

"Don Pearce" wrote in message
...

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.

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

It looks as if the Dolby recommendation for
the shift upwards of 1kHz was not implemented
I still have a lot of reading to do.

Comparison of noise levels using the different weighting
options is interesting.

Iain

Noise Weighting Curves
 

On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...

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.

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

It looks as if the Dolby recommendation for
the shift upwards of 1kHz was not implemented
I still have a lot of reading to do.

Comparison of noise levels using the different weighting
options is interesting.

Iain


Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

d

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

Noise Weighting Curves
 

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:

"Don Pearce" wrote in message
...

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain

Noise Weighting Curves
 

On Thu, 4 Oct 2007 11:11:23 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:33:24 +0300, "Iain Churches"
wrote:

"Don Pearce" wrote in message
...

What are the numbers?

They both peak at 6276 Hz.
The difference between them is 5.6dB
At 6.276kHz the 468 is +12.2db and ARM is 6.6dB

Does anything you have say why the curves go on rising all the way to
beyond 6kHz? That is a long way past the peak of the human hearing
response, and seems a strange thing to do for a noise weighting
system.

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain



OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear. The numbers won't look
anything like as pretty under CCIR 468.

d

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

Noise Weighting Curves
 

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 11:11:23 +0300, "Iain Churches"
wrote:

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain



OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear. The numbers won't look
anything like as pretty under CCIR 468.


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

Iain

Noise Weighting Curves
 

"Iain Churches" wrote in message
ti.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

Noise Weighting Curves
 

On Thu, 4 Oct 2007 11:32:30 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 11:11:23 +0300, "Iain Churches"
wrote:

Don. In a nut-shell, The ITU-R 468 noise weighting curve was
developed by the BBC specifically for noise measurements in
audio equipment. It is said to be better suited in this role than
"A" weighting which is more valid in the measurement of tones
as opposed to noise.


Not only that, but it all goes a very long way above zero and I'm not
too sure I buy that either.

Then the old "A" curve is the one for you:-)
It is described as "benign"

During the 1960s, it became evident that the DIN A-weighting
curve did not give results reflecting a real-world situation.
The BBC's report EL-7 in which the results from various
listening experiments using clicks and tone bursts were
published. Those being tested were then asked to compare
these with a tone of 1kHz. The scores were then compared
with noise levels measured using various weighting filters.

Based upon the work done principally it seems by the BBC,
CCIR recommendation 468-1 was published. There were
further revisions made from time to time, up to revision 4.0.
The curve remained basically unchanged, but tolerances were
specified more accurately. CCIR 468 was subsequently
adopted by the IEC (International Electrotechnical Commission)
and the ITU (International Telecommunications Union) and
became the accepted method for measuring noise in broadcast,
professional audio applications and high-fidelity.
When the CCIR was disbanded in March 1993, the
ITU took over the existing standard.

Iain



OK, thanks for that. It certainly makes for some interesting changes
to the S/N ratios one can claim for audio gear. The numbers won't look
anything like as pretty under CCIR 468.


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

Iain


Just created the curve in my DAW, and it makes white noise look nearly
7dB worse. I haven't tried the A curve, but I imagine that compared to
that, it will be an even bigger change.

d

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

Noise Weighting Curves
 

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


"Iain Churches" wrote in message
hti.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

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

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

Noise Weighting Curves
 

In article i,
Iain Churches wrote:
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

That's not typical.

--
*If you think nobody cares about you, try missing a couple of payments *

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

Noise Weighting Curves
 

On Thu, 4 Oct 2007 20:16:02 +0300, "Iain Churches"
wrote:


"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

Typical of bespoke. To assess typical you need to include all valve
amps in the sum. The average valve amp hums.

Members of a gramophone society really aren't going to own typical
valve amps.

d

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

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
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

That's not typical.

I have a Lowther LL26 (EL 34's PP) 26W at 0.1% THD.
It is half the power of my PPP amp, but still the noise
floor is only 120µV a very presentable -98dB.
It cost £46 in 1968 and was a *very* typical amplifier
of the period.

Both my Radfords (STA 25 and STA 100) are silent,
ear-to-speaker, as are the TL12s.

Don't confuse them with the Dansette:-)

Best regards
Iain

Noise Weighting Curves
 

In article i,
Iain Churches wrote:
Most systems are silent with ear against speaker.

I'm willing to bet they're not.

--
*What boots up must come down *

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

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
Most systems are silent with ear against speaker.

I'm willing to bet they're not.

You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain

Noise Weighting Curves
 

"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

Noise Weighting Curves
 

Don Pearce wrote:
On Thu, 4 Oct 2007 20:16:02 +0300, "Iain Churches"
wrote:

"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

Typical of bespoke. To assess typical you need to include all valve
amps in the sum. The average valve amp hums.

Members of a gramophone society really aren't going to own typical
valve amps.

d


FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The
Beard has a slight hum from the unit (transformers?), but less than some
SS amps I've had.

Noise Weighting Curves
 

On 2007-10-04, Iain Churches wrote:

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
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

That's not typical.

I have a Lowther LL26 (EL 34's PP) 26W at 0.1% THD.
It is half the power of my PPP amp, but still the noise
floor is only 120µV a very presentable -98dB.

Very presentable indeed. I guess I look on amplifier noise floors
as follows:

- specified WRT full power they indicate the absolute maximum dynamic
range available from a system. I'm afraid I'm keen on good dynamic
range.

- specified WRT the nominal 1 W into 8 ohms (2.83 V RMS) you can add the
speaker sensitivity and approximately check if the hiss will be
audible (at 1 m or at the litening position by correcting at 6 dB for
each doubling).

I have heard systems (SS systems) in the past, even at dealers, that
had quite audible noise from the 'speakers and wondered why. It seems
perfectly possible to do an engineering check to see if a system will
exhibit a number of avoidable limitations like this.

I fixed a system some years ago which had a Hafler DH-100 pre-amp with
20 dB of gain from the AUX input, connected to a Quad 405 with its high
gain - somewhat untypical of the US power amps with which the Hafler
might have been designed to work, and some high-ish sensitivity 'speakers.

The combination was noisy. I guess no-one designed it. It just got
assembled. I had to reduce the gain of the preamp (checking it for
stability) to 10 dB, when it just became silent at the listening position.

--
John Phillips

Noise Weighting Curves
 

On 2007-10-04, Don Pearce wrote:
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.

[Noting Don's correction from 19 dB to 9 dB]. May I ask if this
comparison is relevant?

Weighting curves are relative. AFAICS you just can't compare the absolute
audibility of A-weighted noise with ITU-R 486-weighted noise from the
same source. You can only compare weighted figures with the same type
of weighting.

AFAICS, for each weighting the absolute threshold of audibility may be
rather different. What you may get from comparing 468-weighted noise
figures is a more valid comparison WRT human audibility of noise than
from comparing A-weighted noise figures.

--
John Phillips

Noise Weighting Curves
 

"Rob" wrote in message
...

FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The Beard
has a slight hum from the unit (transformers?), but less than some SS amps
I've had.

The Beard valve amps that I have seen perform well. They have fairly small
mains transformers, which are bolted straight to the chassis. Setting them
on rubber grommets (and also tightening the bolts that secure the
laminations)
gets rid of the transformer noise.

Iain

Noise Weighting Curves
 

"John Phillips" wrote in message
...

[Noting Don's correction from 19 dB to 9 dB]. May I ask if this
comparison is relevant?

Maybe not, but it is still fun to do:-)

Weighting curves are relative. AFAICS you just can't compare the absolute
audibility of A-weighted noise with ITU-R 486-weighted noise from the
same source. You can only compare weighted figures with the same type
of weighting.

Manufacturers choose the weighting which shows there amp in the best
possible light, but it is important to compare apples with apples. If all
are
using the same weighting, then there is no problem.

AFAICS, for each weighting the absolute threshold of audibility may be
rather different. What you may get from comparing 468-weighted noise
figures is a more valid comparison WRT human audibility of noise than
from comparing A-weighted noise figures.

Indeed.

Iain

Noise Weighting Curves
 

On Thu, 4 Oct 2007 21:43:04 +0300, "Iain Churches"
wrote:


"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.

I think that whoever came up with that bit of back-pedalling must have
been a politician.

d

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

Noise Weighting Curves
 

Iain Churches wrote:
"Dave Plowman (News)" wrote in message
...

In article i,
Iain Churches wrote:

Most systems are silent with ear against speaker.

I'm willing to bet they're not.


You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain


Of course it does depend on the speakers used.

--
Nick

Noise Weighting Curves
 

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"Dave Plowman (News)" wrote in message
...

In article i,
Iain Churches wrote:

Most systems are silent with ear against speaker.

I'm willing to bet they're not.


You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Iain

--
Nick

Noise Weighting Curves
 

In article i, Iain
Churches wrote:

"Rob" wrote in message
...

FWIW the three bits of valve kit I have (Beard power, AI integrated
and EAR phono), and the one I had (Carmenta pre), are pretty quiet.
The Beard has a slight hum from the unit (transformers?), but less
than some SS amps I've had.

The Beard valve amps that I have seen perform well. They have fairly
small mains transformers, which are bolted straight to the chassis.
Setting them on rubber grommets (and also tightening the bolts that
secure the laminations) gets rid of the transformer noise.

FWIW I had to do something similar with my pair of ESL63s, bought in the
1980s. Also to my old Meridian 200 CD drive... Love the Meridian 263 DAC,
but not really impressed in the end by the drive.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

Noise Weighting Curves
 

Iain Churches wrote:
"Rob" wrote in message
...

FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The Beard
has a slight hum from the unit (transformers?), but less than some SS amps
I've had.

The Beard valve amps that I have seen perform well. They have fairly small
mains transformers, which are bolted straight to the chassis. Setting them
on rubber grommets (and also tightening the bolts that secure the
laminations)
gets rid of the transformer noise.

Iain


Thanks Iain - the transformers are tucked away and last time I looked
they weren't readily accessible, and I suspect they're a fair size given
the amp weighs about 35kg. And if my fettle causes a problem, they're a
problem to replace - £500 each springs to mind.

In use, and for some reason, I'm more forgiving of noise from a valve
amp, although as I say, the ones I have/had are comparable with SS.

Still, next time I open it up I'll have a look.

Rob

Noise Weighting Curves
 

In article ,
Iain Churches wrote:

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"Dave Plowman (News)" wrote in message
...

In article i,
Iain Churches wrote:

Most systems are silent with ear against speaker.

I'm willing to bet they're not.


You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Ah - have you now restricted it to just hum?

Iain

--
Nick

--
*Don't sweat the petty things and don't pet the sweaty things.

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

Noise Weighting Curves
 

"Rob" wrote in message
...
Iain Churches wrote:
"Rob" wrote in message
...

FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The
Beard has a slight hum from the unit (transformers?), but less than some
SS amps I've had.

The Beard valve amps that I have seen perform well. They have fairly
small
mains transformers, which are bolted straight to the chassis. Setting
them
on rubber grommets (and also tightening the bolts that secure the
laminations)
gets rid of the transformer noise.

Thanks Iain - the transformers are tucked away and last time I looked they
weren't readily accessible, and I suspect they're a fair size given the
amp weighs about 35kg. And if my fettle causes a problem, they're a
problem to replace - £500 each springs to mind.

Rob. The Beard that I worked on (SP35 IIRC) had the
mains transformer mounted centre chassis under the rear cage.
Before removing it, check the tightness of the bolts through
the laminations. This might solve the problem completely.

If not, you will need to drill out the transformer mounting
holes to say M8 and then fit the grommets. Put a tab
washer top and bottom, and then ensure that the transformer
bell is grounded to chassis (a separate black wire may
be required with a solder tag at each end from one of the
lamination securing screws to the transformer fixing bolt -
clean off the varnish if required) Don't bolt the transformer
down too tight.

Best regards
Iain

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article ,
Iain Churches wrote:

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"Dave Plowman (News)" wrote in message
...

In article i,
Iain Churches wrote:

Most systems are silent with ear against speaker.

I'm willing to bet they're not.


You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Ah - have you now restricted it to just hum?

No. There is no audible hiss either.
Chocolate Digestive biscuit anyone? :-)

Iain

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:

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

That's not typical.

Bear in mind that traditionally valve amps had AC heaters.
These days, by simply using DC, and biasing the heaters
above the cathode can make 10dB improvement in the
LF noise floor.

In the hey-day of valve amps, iron was cheap and large
electrolytics very very expensive. Now the reverse is the
case. When valve retifiers were used, the reservoir cap was
usually limited to 47µF. Now 470µF is often seen as the first
cap in a chain with one or more chokes of 10 or 20H.
This results in a PSU of low impedance with very
low ripple.

I can understand that it might suit the agenda of some
to try to maintain the idea that valve amps are plagued
with hum and noise:-)

Fortunately, this need not be the case.


Regards to all
Iain