Do you really like the way HDTV looks?

Yes...
Look at the response curves of microphones as an example. Somewhere in the mid
frequency range a standard point close to 1KHZ is usually chosen and the Mic's
response above & below that reference point is measured in db (usually minus)
AKG top of the line condensers have virtually FLAT response chart--that's how
good they are.
Of course a mic's sensitivity is measured in dbM. (-65 comes to mind) This is
an absolute.
My Altec Lansing studio monitors are rated at 99db at 1 watt, one meter distance
on axis. Another absolute.

--
All the Best
Richard Harison
"G-squared" wrote in message
ups.com...
Albert Manfredi wrote:
"Paul Ratcliffe" wrote:

Relative measurements relate two similar quantities - the result
is
dimensionless i.e. it is just a number, it has no units. Therefore
it
is unnecessary and impossible to quote a reference level.

So I take it this means that when an amp is 3 dB down at some
frequency,
it is "unnecessary and impossible" to answer the question "3 dB down

compared to what?"

Bert

In Bert's example, the reference 'level' is generally taken as 1KHz.
This level is temporarily defined as 0 and then the sweep response is
relative to that initial level. Often it is defined at 1 watt out but
it is not etched in stone.

Fluke makes this VERY easy to measure with the 'relative' button on the
meter that defines the present value as '0'

GG




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On 9/25/2006, Paul Ratcliffe posted this:
On Mon, 25 Sep 2006 11:31:14 -0700, Gene E Bloch
wrote:
[...]

Which was what I said before moron Gene E Bloch stuck his oar in and
contradicted.

I will contradict you again, since you are ... wrong.

You really are a "****ing this as pig **** American" aren't you?

I see that you are worth no more of my attention.

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

I take what I just said back!
There is a base for the measurements to which I alluded--therefore relative.
i.e. a mic rated at -65db will deliver c. 2x more output than one rated at -68db
Gotta quit drinking that cheap Jamaican beer!

BTW has anyone else noticed that this thread automatically cross-posts to 2
other groups?

--
All the Best
Richard Harison
"Richard Harison" wrote in message
...
Yes...
Look at the response curves of microphones as an example. Somewhere in the
mid frequency range a standard point close to 1KHZ is usually chosen and the
Mic's response above & below that reference point is measured in db (usually
minus) AKG top of the line condensers have virtually FLAT response
chart--that's how good they are.
Of course a mic's sensitivity is measured in dbM. (-65 comes to mind) This is
an absolute.
My Altec Lansing studio monitors are rated at 99db at 1 watt, one meter
distance on axis. Another absolute.

--
All the Best
Richard Harison
"G-squared" wrote in message
ups.com...
Albert Manfredi wrote:
"Paul Ratcliffe" wrote:

Relative measurements relate two similar quantities - the result
is
dimensionless i.e. it is just a number, it has no units. Therefore
it
is unnecessary and impossible to quote a reference level.

So I take it this means that when an amp is 3 dB down at some
frequency,
it is "unnecessary and impossible" to answer the question "3 dB down

compared to what?"

Bert

In Bert's example, the reference 'level' is generally taken as 1KHz.
This level is temporarily defined as 0 and then the sweep response is
relative to that initial level. Often it is defined at 1 watt out but
it is not etched in stone.

Fluke makes this VERY easy to measure with the 'relative' button on the
meter that defines the present value as '0'

GG




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Newsgroups
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"Richard Harison" wrote in message
...
Yes...
Look at the response curves of microphones as an example. Somewhere
in the mid frequency range a standard point close to 1KHZ is usually
chosen and the Mic's response above & below that reference point is
measured in db (usually minus) AKG top of the line condensers have
virtually FLAT response chart--that's how good they are.
Of course a mic's sensitivity is measured in dbM. (-65 comes to mind)
This is an absolute.
My Altec Lansing studio monitors are rated at 99db at 1 watt, one
meter distance on axis. Another absolute.

In all examples, the Bel (or decibel = 1/10th of a Bel) is a number that
represents a ratio. It's convenient because enormous ratios can be
represented with small numbers, thanks to the log function.

In the amp example, the ratio was output power at a given frequency
compared to output power at some optimal frequency (typically some power
level at 1 KHz for an audio amp). The reference is whatever power level
was used at 1 KHz.

In the radio receiver sensitivity example, the ratio was the lowest
power detectable at the receiver's input compared to 1 mW. The reference
is 1 mW. And by the way, dBm can also be used to express output power at
the transmitter. Again, referenced to 1 mW.

Your 99 dB speaker output volume is probably measured with respect to
sound pressure level, or dB SPL, at 1 meter distance, on axis,
referenced to 20 upascals at that same location. Or sometimes it's
weighted to better represent how loud it appears to a human, and then
called dBA.

But notice how in every instance, the number represents a ratio. It has
to. The equation is always

dB = 10 * logbase10 (power / reference power)

The only thing that changes is what you use as the reference power. So
it's not really correct to differentiate between "absolute" and
"relative." It's always relative. The only question is relative to what?

Bert

"Albert Manfredi" writes:
[...]
So it's not really correct to differentiate between "absolute" and
"relative." It's always relative. The only question is relative to
what?

There is a semantic problem here.

The term absolute means, in this context, known. For example, even
though dBm is "relative" in the sense that it is relative to a
1reference power (1 milliwatt), it is a known quantity since the
reference power is defined. This means (e.g.) dBm is an absolute power
level.
--
% Randy Yates % "...the answer lies within your soul
%% Fuquay-Varina, NC % 'cause no one knows which side
%%% 919-577-9882 % the coin will fall."
%%%% % 'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

Agreed! Relative to a base of some source.
A previous posted point of mine was that SPL is also measured in db. After that
it gets a little vague as to source. What =0db? An anechoic chamber 200 feet
underground? A whisper? Whatever reasoning...there is a "starting point."
I also mentioned that even in the dbSPL world there are 2 "weighting" systems,
"C" and "A." "C" weighting is full frequency, whereas "A" weighting is
condensed to what we actually hear as opposed to what we might "feel." ( for
instance, A low C 32 foot Organ pipe or the HF overtones of a Stradivarius
violin as opposed to a Guarnerius)
In concert sound, I ALWAYS set my SPL meters to "C" weighting! I figured the
audience deserved full frequency, especially those whose ears were able to
appreciate it

--
All the Best
Richard Harison
"Albert Manfredi" wrote in message
...
"Richard Harison" wrote in message
...
Yes...
Look at the response curves of microphones as an example. Somewhere in the
mid frequency range a standard point close to 1KHZ is usually chosen and the
Mic's response above & below that reference point is measured in db (usually
minus) AKG top of the line condensers have virtually FLAT response
chart--that's how good they are.
Of course a mic's sensitivity is measured in dbM. (-65 comes to mind) This is
an absolute.
My Altec Lansing studio monitors are rated at 99db at 1 watt, one meter
distance on axis. Another absolute.

In all examples, the Bel (or decibel = 1/10th of a Bel) is a number that
represents a ratio. It's convenient because enormous ratios can be represented
with small numbers, thanks to the log function.

In the amp example, the ratio was output power at a given frequency compared
to output power at some optimal frequency (typically some power level at 1 KHz
for an audio amp). The reference is whatever power level was used at 1 KHz.

In the radio receiver sensitivity example, the ratio was the lowest power
detectable at the receiver's input compared to 1 mW. The reference is 1 mW.
And by the way, dBm can also be used to express output power at the
transmitter. Again, referenced to 1 mW.

Your 99 dB speaker output volume is probably measured with respect to sound
pressure level, or dB SPL, at 1 meter distance, on axis, referenced to 20
upascals at that same location. Or sometimes it's weighted to better represent
how loud it appears to a human, and then called dBA.

But notice how in every instance, the number represents a ratio. It has to.
The equation is always

dB = 10 * logbase10 (power / reference power)

The only thing that changes is what you use as the reference power. So it's
not really correct to differentiate between "absolute" and "relative." It's
always relative. The only question is relative to what?

Bert




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"Richard Harison" writes:

Agreed! Relative to a base of some source.
A previous posted point of mine was that SPL is also measured in db. After that
it gets a little vague as to source. What =0db? An anechoic chamber 200 feet
underground? A whisper?

dB SPL is a well-defined unit and is the sound pressure level
referenced to 0.0004 dynes/cm^2 or, equivalently, 20 microPascals. If
the sound is traveling in a plane wave, this can also specify sound
intensity and is referenced to 10^{-12} W/m^2.

@BOOK{psychoacoustics,
title = "{Psychoacoustics: Facts and Models}",
author = "E.~Zwicker and H.~Fastl",
publisher = "Springer",
edition = "second",
year = "1999"}
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..."
%%% 919-577-9882 %
%%%% % 'Eldorado Overture', *Eldorado*, ELO
http://home.earthlink.net/~yatescr

Thanks...
I was trying to make reference to human terms. (normal conversation= 70 db SPL,
Lear Jet @ 20 feet(been there) 170 dbSPL

--
All the Best
Richard Harison
"Randy Yates" wrote in message ...
"Richard Harison" writes:

Agreed! Relative to a base of some source.
A previous posted point of mine was that SPL is also measured in db. After
that
it gets a little vague as to source. What =0db? An anechoic chamber 200 feet
underground? A whisper?

dB SPL is a well-defined unit and is the sound pressure level
referenced to 0.0004 dynes/cm^2 or, equivalently, 20 microPascals. If
the sound is traveling in a plane wave, this can also specify sound
intensity and is referenced to 10^{-12} W/m^2.

@BOOK{psychoacoustics,
title = "{Psychoacoustics: Facts and Models}",
author = "E.~Zwicker and H.~Fastl",
publisher = "Springer",
edition = "second",
year = "1999"}
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..."
%%% 919-577-9882 %
%%%% % 'Eldorado Overture', *Eldorado*, ELO
http://home.earthlink.net/~yatescr



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"Richard Harison" writes:

Thanks...
I was trying to make reference to human terms. (normal conversation= 70 db SPL,
Lear Jet @ 20 feet(been there) 170 dbSPL

You also stated that SPL is measured in dB. That is incorrect. "dB"
and "dB SPL" are two different units. The first is relative
(unitless), the second is absolute.

Yes, normal conversation is about 70 dB SPL. I don't think a jet, even
at 20 feet, is 170 dB SPL. You would lose your hearing within a few
seconds at that level. The following lists at 140 dB SPL a jet engine
at 3m.

http://www-ccrma.stanford.edu/~jos/mdft/DB_SPL.html

Historically 0 dB SPL was a measurement of the quietest sound a human
could hear at their peak sensitivity of around 4 kHz.

--Randy




--
All the Best
Richard Harison
"Randy Yates" wrote in message ...
"Richard Harison" writes:

Agreed! Relative to a base of some source.
A previous posted point of mine was that SPL is also measured in db. After
that
it gets a little vague as to source. What =0db? An anechoic chamber 200 feet
underground? A whisper?

dB SPL is a well-defined unit and is the sound pressure level
referenced to 0.0004 dynes/cm^2 or, equivalently, 20 microPascals. If
the sound is traveling in a plane wave, this can also specify sound
intensity and is referenced to 10^{-12} W/m^2.

@BOOK{psychoacoustics,
title = "{Psychoacoustics: Facts and Models}",
author = "E.~Zwicker and H.~Fastl",
publisher = "Springer",
edition = "second",
year = "1999"}
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..."
%%% 919-577-9882 %
%%%% % 'Eldorado Overture', *Eldorado*, ELO
http://home.earthlink.net/~yatescr



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--
% Randy Yates % "So now it's getting late,
%% Fuquay-Varina, NC % and those who hesitate
%%% 919-577-9882 % got no one..."
%%%% % 'Waterfall', *Face The Music*, ELO
http://home.earthlink.net/~yatescr

Randy Yates writes:
[...]
dB SPL is a well-defined unit and is the sound pressure level
referenced to 0.0004 dynes/cm^2

Wups! Wrong. The correct value is 0.0002 dynes/cm^2.
--
% Randy Yates % "Bird, on the wing,
%% Fuquay-Varina, NC % goes floating by
%%% 919-577-9882 % but there's a teardrop in his eye..."
%%%% % 'One Summer Dream', *Face The Music*, ELO
http://home.earthlink.net/~yatescr