3 dB bandwidth

dBA is a measurement of sound levels, using an 'A' filter (weighting), which is intended to match the sensitivity of the human ear. Surprisingly, there is a bBb and dBc too. ;-)

At 1kHz about 3.16pW (-85dBm). or 0dBm = +85dBa.

--
  Keith

Well, notwithstanding we don't have e fingers, and four in base two counting on fingers is dirty, I'm pretty sure that the reason we decided on base 10 is because that's how many fingers plus thumbs that most pepole have.

Did you know that your forearm is exactly one cubit long? ;-)

Well, obviously the base 10 system was invented by women. If it had been invented by men, it'd have been One, two, three, four, five, six, seven, eight, nine, ten,

Eleven! ;-P

--
Cheers!
Rich

RELATIVE TO WHAT!!!?!?!?!??!???!!?!?!?

Decibels are _a ratio_.

So, a jet engine is putting out 120 dBA. Decibels on the A curve, relative to WHAT!????!?!??

"The threshold of hearing"? Oh, that's a great reproducible calibratable standard. "The noise produced by a baby mouse urinating on a desk blotter"?

At least Ghee Massawn came up with absolute pressure in nanoPascals per square centimeter or something, whatever the f*ck a "nanoPascal" is.

Thanks, Rich ------ "Tourist to New Yorker: "Pardon me, sir, do you know what time it is, or should I just go f*ck myself?""

dBA SPL is referenced to a pressure value of 0.0002 dynes/cm2 at 1Khz, which is the median threshhold of hearing in humans.

The A refers to A weighting. Human ears aren't even close to being equally sensitive at all frequencies, and the variance is greater at low SPLs than at high SPLs. IIRC, A weighting is used for SPLs below

55 dB, B weighting is for SPLs between 55 and 85 dB, and C weighting is used for measuring SPLs of 85 dB or higher.

You can hear better than that ? A few ppl can it's true. Me amongst them. Nevertheless +0 -0.5dB is 'light years' better than the old presumed ( by carpet slippered pipe smoking buffoons ) adequate +/- 3dB.

Since the -0.5 dB point in my gear is typically @ 5 Hz or 50kHz I trust you'll see that the audio band is impeded not one iota.

You use instrumentation gear for your 'hi-fi' ? Much more likely Sony or another reasonable brand.

I think you just proved why dBs are preferred. Linear numerical representation is simply not very instinctively communicative.

It's meant as a joke actually but I regret that it may be uncommonly close to the truth.

I was once with an agency that placed me in a new position. It was great

- I even got a brand new company car ( 2 litre injection ) of my own choice. That's *very* rare in plain engineering I can tell you !

Sadly the job didn't work out as well as hoped for 'political' reasons.

Later, they placed my details with the renowned audio firm 'Quad' or the Acoustical Manufacturing Company Ltd to give them their real name . They liked my CV but rejected my application for the post of technical director simply on the basis that I was *too young* ! At age 35 would you believe ?

They were certainly the carpet slippered pipe smoking types and what they actually *needed* was a 35 yr old to poke a stick up their collective arse !

Anyway - the Chinese bought them now.....

Uh ? Your point is ? How's your Alzheimers ?

Graham

Incorrect !

The dBv ( note little v ) was briefly introduced as a measure that represented in voltage terms the equivalent of 0dBm ( 600ohms ). Meaning 0.775 V rms.

This was in the time that the pro-audio world was struggling to extract itself from the tyranny of the matched-impedance dBm.

The dBv was a good idea but was indeed too confusingly close to the dBV. It eventually became the dBu. The unit of measurement universally used in all decent audio specs today.

For a modern dB spec see the IEC ( International Electrotechnical Commision ).

Graham

I suspect they're extinct actually !

Graham

Hmmmm.... As an AES member I *cannot* re-distribute internal documents sadly ( even for educational purposes ) without prejudicing my member status.

If you visit the AES site there are a number of documents that are downloadable pdfs on a 'complimentary' basis however.

For the same reason it was rejected back around 1974. Namely commonality with established practice.

If there was any time to make a change it was *then* ! Leaving it decades later was preposterous ! I guess they had to revisit the concept and rejected it for the same reasons as before.

Graham

Strangely enough I had a similar thought.

If humans had 4 fingers per hand or maybe 8, would we be having this discussion about octiBels or hexiBels ?

Graham

Apparently that's not good enough anymore !

It's dB ( SPL ) A-wtd or alternatively it's dB ( SPL ) C-wtd.

You can also use dB ( 20uPa ) A-wtd etc......

Talk to the IEC if you have a problem with this. ;-)

Grham

Instinctively, to me "dBm" suggests relative to 1 milliwatt in 50 ohms, rather than 600. It must be a culture thing.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Didn't they know about left-hand threads?

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

OMG !

Someone finally got it !

Cheers, Graham

Relative to 20 microPascals actually !

See the definition !

Errrr - I just actually posted the definition. It's above. dB ( 20uPA ). also simply known as dB ( SPL ) or dB for short when it's clear that acoustic dBs are the subject.

Actually it's highly verifiable.

20uPa *is* a presure you clown ! Pascals = Newtons/ metre ^2

If you ppl gave up your precious inches and ounces maybe you might understand International Units better !

Graham

There's absolutely no problem with that. The RF guys adopted the dB for its ease of use too.

The preferred usage in your case would be dB ( 50 ohms ). This resolves to a different voltage for 0dBm compared to audio usage but that's understood on account of the impedance reference.

The dB is wonderfully adaptable. You can refer it to anything you like.

Graham

GOTCHA!!!

Your pretending to not know what a pascal is undermined by the fact that you mentally converted dynes/cm2 to Pascals... :)

While the threshhold of hearing in humans has large variations, the *median* threshhold of hearing in humans is a reproducible and calibratable standard especially once you notice how close it is to 0.0002 dynes/cm2 at 1Khz and define it as that, making it into a unit that is derived from the Dyne and the Meter.

What are you drivelling on about now ?

It's called the metre btw.

A meter is the thing you use to measure voltages and stuff. I see you're incapable of distinguishing metric standard units from what you might have in your toolbox !

Graham

There's a substantial simplification that's possible, with a simple class-A emitter follower A2 to the high-voltage rails. A1 supplies all the gain, but is relieved from having a good CMRR spec. The EF only has to supply the current to drive A3 stage's input resistor.

. +/-200V +230V . input _________________| ____ . A1 _| +5F | | R/100 . o-/\\/\\-+----|+ \\ A2 _| 5V ,---/\\/---, . | | >-------------| \\ | R | A3__ | +/-2V . prot ,-|-_/ biased | >---+-+--+--/\\/-+--|- \\ | output . | | | -5F emitter |__/ | | | >--+-- A/D . guard | | | followers | | 5V ,--|+_/ . o-----+--+---| ----------------| ------' | | . infinite |_________________| _________| gnd . Zin input | . -230V

I expanded the operating range to +/-210 volts.

--
 Thanks,
    - Win

So the re-definition of the decibel is an internal document?

I think the time has come to draw this nonsense to a close before you or Kevin tell us that the volt and ampere have also been re-defined to suit the convenience of audio engineers.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk