[Les Cargill]

wrote:

On Jul 29, 10:14 pm, Les Cargill wrote:

0dB is an unatainable acoustic SPL level meaning
the threshold of audibility. That means "no signal"
for all intents and purposes.


Uhm, no, emphatically so at that.

0 dB SPL refers to an AVERAGE threshold sound pressure
level achieved during a rather extensive set of testing over
a half century ago. It is the NORMALIZED average threshold
at 1 kHz. In fact, the average curve shows the threshold
lower by 6 dB at 4 kHz in most test subjects. That alone
puts false your claim that 0dB SPL is "unnattainable."

Secondly, the notion that 0 dB SPL means "no signal
for all intents and purposes" is simply nonsense. That
figure is achieved over the measurement or detection
bandwidth and represents the ability to differentiate
the signal form the noise. Narrow the detection
bandwidth, and immediately that threshold lowers. The
ear represents (approximately) a 1/3 octave-wide filter
at medium and high frequencies: simply narrow that
bandwidth and you can easily detect signals lower.

Now, one may argue that you can't "narrow the
bandwidth" of the ear. That, however, belies your
broad, blanket claim of "no signal, for ALL intents
and purposes."


Point well taken - I did not specify any sort of
context at all. FWIW, I meant in terms of acoustic
output from ( I presume ) a PA system. Heck, the
hiss from most PA are well over any sort of realistic
figure discussed so far.

And, lastly, your premise that 0 dB represents NO signal
is simply false on its face. Once again, look at the
definition:

dB = 10 * log (P1/P2)

and if you have 0 dB, then P1/P2 must be equal to
one.

In most instances I and most people are aware of,
"no signal" means "0 signal", and 0 is not equal to 1.


True!

--
Les Cargill

[jim Gregory]

T - I never use Mister
Mea culpa, yes, Watts rms is an invalid term, I meant I had rarely measured
wattages of steady-state power levels.
Jim

"Mr.T" MrT@home wrote in message
u...

"jim Gregory" wrote in message
...
In 40+ years of studios maintenance/design I rarely measured Watts rms as
I
usually dealt with voltage amplifiers.

I'd be more surprised if you HAD measured "watts RMS" !
:-)

MrT.

[William Sommerwerck]

In 40+ years of studios maintenance/design I rarely
measured watts RMS as I usually dealt with voltage
amplifiers.

I'd be more surprised if you HAD measured "watts RMS"!

Mea culpa, yes, watts RMS is an invalid term. I meant I
had rarely measured wattages of steady-state power levels.


Whoa! Error upon error upon error...

RMS -- root-mean-square -- is a measurement of AC voltage or current that
produces a heating effect equivalent to a DC voltage of the same value --
eg, an AC voltage of 1V RMS heats a resistor as much as 1V DC.

"Watts RMS" is a perfectly valid term that applies to a mathematically
definable measurement. The problem is that it has no known relationship to
any meaningful real-world evaluation.

RMS measurements have nothing to do with whether the signal varies or is
"steady state".

[fredbloggstwo]

"Eeyore" wrote in message
...


"Roy W. Rising" wrote:

Eeyore wrote:
"Roy W. Rising" wrote:

"Zero dB" is a reference point for metering. It has been set
differently for various systems. Sometimes it's 0dB = 0VU = +4dBm.

+4dBu please ! :-)

You're welcome to add "Sometimes it's 0dB = +4dBu" if that's what
*pleases*
you, but sometimes it's been +8dBm as well ... and that in a 150ohm
environment! ;-)

I'm pointing out that dBu =/= dBm. Almost nothing uses dBm any more in pro
audio
and hasn't done for about 40 years. dBm is a POWER, and dBu is a VOLTAGE.
A VU
meter measures voltage not power. We do not 'impedance amtch' audio
circuits for
maximum power transfer these days and the dBm died with that.

Just show me one piece of modern kit with 150 ohm output Z and 150 ohm
input Z !

Ehhhh, telephone circuits in the UK are all still 600 ohm and the level is
measured in dBm - as a power unit. All equipment connected are either
terminating (RL = 600 ohm) or bridging (RL = 10kohms)

Mike


Graham

[Eeyore]

fredbloggstwo wrote:

"Eeyore" wrote in message

Just show me one piece of modern kit with 150 ohm output Z and 150 ohm
input Z !

Ehhhh, telephone circuits in the UK are all still 600 ohm and the level is
measured in dBm - as a power unit. All equipment connected are either
terminating (RL = 600 ohm) or bridging (RL = 10kohms)

Since when was the PSTN considered 'pro audio' ?

Graham

[[email protected]]

On Aug 3, 2:30 pm, Eeyore
wrote:
fredbloggstwo wrote:
"Eeyore" wrote in message

Since when was the PSTN considered 'pro audio' ?

Graham

Graham,

See your discussion about "MBAs" above. I have had similar
situations to those you described awhile back and let me tell you
there are a few that would try to tell me PSTN was as good as 'pro
audio', mp3 at 64kbs was more than good enough, etc. etc. I think most
of them are deaf and suffering from SFB.

Bob Smith
BS Studios
we organize chaos
http://www.bsstudios.com

[Roy W. Rising[_2_]]

Eeyore wrote:
fredbloggstwo wrote:

"Eeyore" wrote in message

Just show me one piece of modern kit with 150 ohm output Z and 150
ohm input Z !

Ehhhh, telephone circuits in the UK are all still 600 ohm and the level
is measured in dBm - as a power unit. All equipment connected are
either terminating (RL = 600 ohm) or bridging (RL = 10kohms)

Since when was the PSTN considered 'pro audio' ?

Graham

Pro audio notwithstanding, the dBm is alive and well, and an important
reference in the *world* of sound. To deny its importance is tantamount to
saying "let them eat treacle". Furthermore, this thread is about "0 dB", a
reference that can be applied to *many* things.

--
~
~ Roy
"If you notice the sound, it's wrong!"

[Eeyore]

"Roy W. Rising" wrote:

Eeyore wrote:
fredbloggstwo wrote:

"Eeyore" wrote in message

Just show me one piece of modern kit with 150 ohm output Z and 150
ohm input Z !

Ehhhh, telephone circuits in the UK are all still 600 ohm and the level
is measured in dBm - as a power unit. All equipment connected are
either terminating (RL = 600 ohm) or bridging (RL = 10kohms)

Since when was the PSTN considered 'pro audio' ?


Pro audio notwithstanding, the dBm is alive and well, and an important
reference in the *world* of sound. To deny its importance is tantamount to
saying "let them eat treacle". Furthermore, this thread is about "0 dB", a
reference that can be applied to *many* things.

I've never denied its importance in realms where impedance matched circuits are
important. Notably RF. Pro-audio simply doesn't require them though.

Graham

[Roy W. Rising[_2_]]

Eeyore wrote:
"Roy W. Rising" wrote:

Pro audio notwithstanding, the dBm is alive and well, and an important
reference in the *world* of sound. To deny its importance is
tantamount to saying "let them eat treacle". Furthermore, this thread
is about "0 dB", a reference that can be applied to *many* things.

I've never denied its importance in realms where impedance matched
circuits are important. Notably RF. Pro-audio simply doesn't require them
though.

Graham

Let's call it a standoff by adding "except when it does".

--
~
~ Roy
"If you notice the sound, it's wrong!"

[Ron Capik]

William Sommerwerck wrote:

Well, not really...

I just came in on this, so if I'm repeating something, I apologize.

0dB, as someone else pointed out, is a specific, arbitrary power level. It
has nothing to do with gain, per se; it is a reference point for gain
_changes_.

Also, a device can have a _voltage_ gain or loss, yet have a _power_ gain of
0dB.

Speaking of arbitrary, could someone explain the Verizon FIOS
[optical fiber to the home] ad where the tech guy tells the kid a
bunch of techno babble including " ...light so clean it's 20 dB hot" ?



Later...

Ron Capik
--

[Don P.]

Ron Capik scribbled:


Speaking of arbitrary, could someone explain the Verizon FIOS
[optical fiber to the home] ad where the tech guy tells the kid a
bunch of techno babble including " ...light so clean it's 20 dB hot" ?


Well, I haven't seen the ad, but it sounds to me to be rather similar in
function to the power generation that is produced by the modial
interactions of magneto-reluctance and capacitive directance, first
produced in the retro-encabulator from Rockwell Systems.

The main winding was of the normal lotus-o-delta type placed in panendermic
semiboloid solts in the stator, every seventh conductor being connected by
a non-reversible termic pipe to the differential girdlespring on the 'up'
end of the grammeter.

Anyway, It has been successfully used for operating nofer trunnions. In
addition, whenever a barescent skor motion is required, it may be employed
in conjunction with a drawn reciprocating dingle arm to reduce sinusoidal
depleneration.

Hope that clears things up.

[Ron Capik]

"Don P." wrote:

Ron Capik scribbled:


Speaking of arbitrary, could someone explain the Verizon FIOS
[optical fiber to the home] ad where the tech guy tells the kid a
bunch of techno babble including " ...light so clean it's 20 dB hot" ?

Well, I haven't seen the ad, but it sounds to me to be rather similar in
function to the power generation that is produced by the modial
interactions of magneto-reluctance and capacitive directance, first
produced in the retro-encabulator from Rockwell Systems.

The main winding was of the normal lotus-o-delta type placed in panendermic
semiboloid solts in the stator, every seventh conductor being connected by
a non-reversible termic pipe to the differential girdlespring on the 'up'
end of the grammeter.

Anyway, It has been successfully used for operating nofer trunnions. In
addition, whenever a barescent skor motion is required, it may be employed
in conjunction with a drawn reciprocating dingle arm to reduce sinusoidal
depleneration.

Hope that clears things up.

Yes, in all three spectrums. I'm surprised
by the Rockwell Systems. Anyway, I knew
someone here could make sense of it.
No question, ...It's true quam.

Thanks


Later...

Ron Capik cynic in training
--