Reply by glen herrmannsfeldt●March 1, 20052005-03-01
Jon wrote:
(snip)
> "RMS power" is just an incorrect term for "average power" which is
> determined using an RMS amplitude.
Well, the FTC version had to do with amplifier marketers using
peak power, which may be the maximum power it could put out for
a very short time will self-destructing. I believe, then, that
RMS power has a time duration that it must be measured over.
While one cycle would normally be enough, I believe the FTC
requires something like 20 minutes.
-- glen
Reply by ●March 1, 20052005-03-01
Jon <u035m4i02@sneakemail.com> writes:
> [...]
> "RMS power" is just an incorrect term for "average power" which is
> determined using an RMS amplitude.
Jon, I believe this terminology may be a remnant of the audio era
circa the 60s and 70s in which some audio power amplifier manufacturers
would quote "peak power" instead of "RMS power," thereby artificially
inflating their power ratings.
Note also that, when measuring power in the real-world, it is always
appropriate to ask what the averaging time is.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124
Reply by Jon●March 1, 20052005-03-01
glen herrmannsfeldt wrote:
> Well, the 20*log10 gives (relative) power in dB from an amplitude
> (voltage or current).
well dB isn't a power, it's a ratio.
but since it was originally defined as a power ratio, the formula needs
to be changed to make it consistent with amplitudes?
still don't understand digital "power". :-) it's on the tip of my
brain, though...
> RMS voltage or current give the same average power as a DC voltage or
> current and a given resistor. In that sense, there is no meaning to RMS
> power.
"RMS power" is just an incorrect term for "average power" which is
determined using an RMS amplitude.
--
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Reply by Jon●March 1, 20052005-03-01
Tim Wescott wrote:
> Both abbreviations and acronyms should be written out with all caps
> -- although some acronyms get into lower case laser-quick; you have
> to keep your radar screens in tune to find all the cases but even
> then you can run into the occasional snafu.
those aren't acronyms anymore. they've become words and therefore can
be written in lowercase. as for how an acronym like RMS can become
lowercase without the capacity to become a word ("erms?") here is one
potential reason:
>> "rms" is written in lower-case because that follows the general
>> accepted practice as outlined in the Abbreviations Dictionary, 9th
>> ed. (Ralph De Sola, Dean Stahl and Karen Kerchelich; CRC Press
>> ISBN0-8493-8944-5, 1995) and other sources. Quoting the CRC book:
>> "American as well as British and Canadian publishers appear to be
>> following the trend to capitalize only those letters normally
>> capitalized: proper nouns and important words in titles. They reserve
>> lowercase letters for abbreviations consisting of adjectives and
>> common nouns." This is the way it appears in the IEEE reference
>> above. Other popular examples are "rpm," and "mph."
doesn't explain why we don't also have "thd+n", "imd", "snr", "cmrr",
and "cd-r". so i think it's safe to assume that the language is just
screwy and we can do whatever we want.
--
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with the spam).
Reply by Randy Yates●February 28, 20052005-02-28
Tim Wescott <tim@wescottnospamdesign.com> writes:
> Randy Yates wrote:
>
>> Tim Wescott <tim@wescottnospamdesign.com> writes:
>>
>>>[...]
>>> Both abbreviations and acronyms should be written out with all caps
>> Proof by assertion? I've given a legitimate, formal case where
>> they're
>> not, so such a statement without any justification sounds a lot like
>> braggadoccio.
>
> Yes, by god! You're too used to mathematics where that's Against the
> Rules -- this here be Style! I mean, if e e cummings can get away
> without caps in his _name_, for crying out loud, surely I can make
> such assertions?
>
> Perhaps you should re-read my post, ask yourself where the words
> "laser", "radar" and "snafu" came from, and note the case of the
> letters that I used.
So, you mean this was a joke? Man, I'm getting slower every year.
--
% Randy Yates % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC % you still wander the fields of your
%%% 919-577-9882 % sorrow."
%%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr
Reply by glen herrmannsfeldt●February 28, 20052005-02-28
Jon wrote:
(snip)
> Oh yeah, dB are technically related to power levels in the first place
> (10*log10) and voltage decibels are a 20*log10 afterthought. I assume
> the dB I am using on screen are related to 20*log10, because they are
> referring to amplitude levels.
Well, the 20*log10 gives (relative) power in dB from an
amplitude (voltage or current).
> Hmmm... but the "average RMS power" is
> expressed in dB(FS?) as well. Ok I think this is making some sense...
It was my understanding that there was no such thing as RMS
power until the FTC set the requirements for audio power
amplifier measurements. Not only did they define RMS power, but
they require that an amplifier (or receiver) model number not be
twice the watts/channel of the amplifier. (So as not to deceive
people.) There are some 200W/channel amplifiers with a model
number of 401 just to get around that law.
RMS voltage or current give the same average power as a DC
voltage or current and a given resistor. In that sense, there
is no meaning to RMS power.
-- glen
Reply by Jerry Avins●February 28, 20052005-02-28
robt bristow-johnson wrote:
> in article WaqdnUc_W78tPL_fRVn-rg@rcn.net, Jerry Avins at jya@ieee.org wrote
> on 02/27/2005 23:44:
>
>
>>It was a sad day for us when my wife-to-be and I found "E. E. Cummings"
>>in the Boston phone directory.
>
>
> listen, i've been trying to get those bastards to stop abbreviating my name
> as Robt. who the fuck is "Robt"?! Robot?? and they haven't gotten my
> address right either. after nearly 5 years. bastards.
>
> if they don't (or didn't) respect ol' e.e., they ain't gonna respect fred
> harris either. (my decapitalizations exist only in the cyber-slew.)
You think you have trouble? There were once three different listings in
the Brooklyn phone directory with my number. One was mine, and one was
for somebody a few miles away. The third was for someone way out of the
exchange area who happened to have the same name as an an acquaintance
in Greenwich Village. (We had a bit of fun with that.)
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Bhaskar Thiagarajan●February 28, 20052005-02-28
"Jon" <u035m4i02@sneakemail.com> wrote in message
news:422137C3.8060602@sneakemail.com...
> Tim Wescott wrote:
>
> > If the digital signal is a linear representation of a real-world signal
> > then the "digital power" will be proportional to real power -- so if a
> > "digital power" of 0.1 (full scale)^2/sec generates a 2.5 watt output
> > then a "digital power" of 1.0 (full scale)^2/sec will generate 25 watts.
>
> Ok, I kind of understand.
>
> > Your mention of dB_FS is more to the point: expressing gains and signal
> > levels in dB is extremely convenient in signal processing. The fact
> > that it implies a power level may be confusing, but as I stated before
> > if the processing is all linear then you will ultimately be able to
> > equate it to an input power or an output power.
>
> Oh yeah, dB are technically related to power levels in the first place
> (10*log10) and voltage decibels are a 20*log10 afterthought. I assume
> the dB I am using on screen are related to 20*log10, because they are
> referring to amplitude levels. Hmmm... but the "average RMS power" is
Jon - I don't think there is 'voltage decibel' and a 'power decibel'. There
is just decibel.
If you have voltage values to start with, then your conversion to dB uses a
certain formula (20*log10) and if you have power values, you use another
(10*log10).
Perhaps, this separation in thought will help make things more clear for
you.
> expressed in dB(FS?) as well. Ok I think this is making some sense...
>
> --
> Include "newsgroup" in the subject line to reply by email (or get dumped
> with the spam).
Reply by robert bristow-johnson●February 28, 20052005-02-28
in article WaqdnUc_W78tPL_fRVn-rg@rcn.net, Jerry Avins at jya@ieee.org wrote
on 02/27/2005 23:44:
> It was a sad day for us when my wife-to-be and I found "E. E. Cummings"
> in the Boston phone directory.
listen, i've been trying to get those bastards to stop abbreviating my name
as Robt. who the fuck is "Robt"?! Robot?? and they haven't gotten my
address right either. after nearly 5 years. bastards.
if they don't (or didn't) respect ol' e.e., they ain't gonna respect fred
harris either. (my decapitalizations exist only in the cyber-slew.)
--
r b-j rbj@audioimagination.com
"Imagination is more important than knowledge."
Reply by Jerry Avins●February 28, 20052005-02-28
Tim Wescott wrote:
> Randy Yates wrote:
>
>> Tim Wescott <tim@wescottnospamdesign.com> writes:
>>
>>> [...]
>>> Both abbreviations and acronyms should be written out with all caps
>>
>>
>>
>> Proof by assertion? I've given a legitimate, formal case where they're
>> not, so such a statement without any justification sounds a lot like
>> braggadoccio.
>
>
> Yes, by god! You're too used to mathematics where that's Against the
> Rules -- this here be Style! I mean, if e e cummings can get away
> without caps in his _name_, for crying out loud, surely I can make such
> assertions?
>
> Perhaps you should re-read my post, ask yourself where the words
> "laser", "radar" and "snafu" came from, and note the case of the letters
> that I used.
It was a sad day for us when my wife-to-be and I found "E. E. Cummings"
in the Boston phone directory.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������