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Trying to understand "professional levels"

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April 24, 2005 5:34:47 AM

Archived from groups: rec.audio.pro (More info?)

I've read that professional gear operates with a "hotter" signal. It's not
clear to me what exactly this means or why it would make a difference.

Using my Marshall MXL LDC running through a VTB-1 pre, I can record an
instrument such as a acoustic guitar so that it's either barely audible or
more than loud enough to clip. What would be the benefit of a hotter signal?
There must be a reason why everyone talks about this, so I must have an
incomplete understanding of something.
Anonymous
April 24, 2005 5:34:48 AM

Archived from groups: rec.audio.pro (More info?)

Doc <docsavage20@xhotmail.com> wrote:
>I've read that professional gear operates with a "hotter" signal. It's not
>clear to me what exactly this means or why it would make a difference.

It means that typical professional gear requires a higher voltage on the
input to get "nominal level." It doesn't make that much of a difference,
it's really just a legacy standard.

>Using my Marshall MXL LDC running through a VTB-1 pre, I can record an
>instrument such as a acoustic guitar so that it's either barely audible or
>more than loud enough to clip. What would be the benefit of a hotter signal?

If you were going into an input designed for a hotter signal, it wouldn't
clip so easily. +4 inputs are designed to take higher levels without
overloading. +4 outputs are designed to deliver higher levels without
overloading.

>There must be a reason why everyone talks about this, so I must have an
>incomplete understanding of something.

People worry too much.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 24, 2005 5:34:48 AM

Archived from groups: rec.audio.pro (More info?)

"Doc" <docsavage20@xhotmail.com> wrote in message
news:XICae.12345$go4.8726@newsread2.news.atl.earthlink.net...
> I've read that professional gear operates with a "hotter" signal. It's not
> clear to me what exactly this means or why it would make a difference.
>
> Using my Marshall MXL LDC running through a VTB-1 pre, I can record an
> instrument such as a acoustic guitar so that it's either barely audible or
> more than loud enough to clip. What would be the benefit of a hotter
> signal?
> There must be a reason why everyone talks about this, so I must have an
> incomplete understanding of something.
>
>

A "hotter" signal, +4db for professional signals as opposed to -10db for
consumer levels lowers the noise floor with respect to the signal applied.
In other words, when your signal works to a higher peak, the noise inherent
in audio the devices it passes through is further below, and therefore less
audible. The higher a mountain is, the further away the land from which it
protrudes.
Related resources
Anonymous
April 24, 2005 5:34:48 AM

Archived from groups: rec.audio.pro (More info?)

"Doc" wrote ...
> I've read that professional gear operates with a "hotter" signal.
> It's not clear to me what exactly this means or why it would
> make a difference.

Tradition and convention. "Professional" equipment tends to use
the signal levels (but less so the impedances) common from
telephone equipment going back the better part of 100 years ago.
Generally speaking, "pro" equipment is standardized at +4dB and
"consumer" at -10dB. (dB references intentionally omitted from
this discussion for simplicity and because it seems outside the
scope at this point.)

There are devices and methods for interfacing pro and consumer
equipment, and sometimes people even just hook them together
without benefit of any special treatment.

> Using my Marshall MXL LDC running through a VTB-1 pre,
> I can record an instrument such as a acoustic guitar so that it's
> either barely audible or more than loud enough to clip. What
> would be the benefit of a hotter signal? There must be a reason
> why everyone talks about this, so I must have an incomplete
> understanding of something.

Setting operating/recording levels is really independent of the
interface voltages ("pro" +4dB vs. "consumer" -10dB)

Very generally, set your operating and/or recording level so that
the loudest expected sound is some safe margin below full-scale
(clipping). "Safe" depends on what you are recording, and what
equipment you are using. It may run from something as little as
3dB below FullScale (-3dBFS) for very predicable sounds to
maybe -20dBFS for unpredictable live recording, etc. The
objective is to achieve the maximum safe recording level to
benefit from the largest dynamic range. i.e, you want to avoid
clipping at the top and stay out of the noise "mud" at the bottom.
Anonymous
April 24, 2005 11:07:37 AM

Archived from groups: rec.audio.pro (More info?)

Doc wrote:

> I've read that professional gear operates with a "hotter" signal.

Putting into numbers which some people around here hate:

Consumer gear line level inputs and outputs work with maximum levels
between 0.1 volt and 2.5 volts. 0.3 volts to 1.5 volt is a more
common range. 1 volt peak is a common medium signal voltage.

Pro gear works line levels that have maximum levels between about 0.3
volts (-10) 1.25 (+4) and up to about 10 volts (+22) with a few pieces
going higher.

Note that with pro gear we actually have common names for these
various levels. They aren't cast in cement because most gear has
headroom. That means that a piece of gear specd at +4 will have
6-10-18 dB of headroom over 1.25 volts before it clips. IOW it will
handle like 2.5 or 6.8 or even more than 10 volts without clipping.

> It's not clear to me what exactly this means or why it would make a
> difference.

Figure that your average piece of pro gear has line-level voltages
that are about 10 dB more than your average piece of consumer gear. 10
dB is very noticable. It can cause trouble with clipping or noise.

> Using my Marshall MXL LDC running through a VTB-1 pre, I can record
an
> instrument such as a acoustic guitar so that it's either barely
> audible or more than loud enough to clip. What would be the benefit
> of a hotter signal?

Depends what you are doing. If what you got works for you, then invoke
that well-known rule about not fixing things that aren't broke.

>There must be a reason why everyone talks about
> this, so I must have an incomplete understanding of something.

Hope my numbers help. ;-)
Anonymous
April 24, 2005 1:32:09 PM

Archived from groups: rec.audio.pro (More info?)

Jonny Durango <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote:
>
>Everyone seems to be missing the point that not only is pro line level
>stronger than consumer, it's also measured on a different scale (dBu
>instead of dBV). dBu is referenced to 0.775 volts (1 mw into 600 ohms)
>and dBV is referenced to 1 volt (1 mw into 1000 ohms). Therefor, -20dBu
>is NOT equal in voltage to -20dBV, nor is pro line level 14 db stronger
>than consumer.

Well, the real point is that is _is_ measured on a known scale. Whereas
the consumer reference levels are all over the place from one piece of
equipment to another (in spite of that -10 dBV standard that not all
manufacturers follow).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 24, 2005 3:46:01 PM

Archived from groups: rec.audio.pro (More info?)

Jonny Durango wrote:
> Doc wrote:
>> I've read that professional gear operates with a "hotter" signal.
>> It's not clear to me what exactly this means or why it would make a
>> difference. Using my Marshall MXL LDC running through a VTB-1 pre, I
>> can record
>> an instrument such as a acoustic guitar so that it's either barely
>> audible or more than loud enough to clip. What would be the benefit
>> of a hotter signal? There must be a reason why everyone talks about
>> this, so I must have an incomplete understanding of something.
>>
>>
>
> Everyone seems to be missing the point that not only is pro line level
> stronger than consumer, it's also measured on a different scale (dBu
> instead of dBV). dBu is referenced to 0.775 volts (1 mw into 600 ohms)
> and dBV is referenced to 1 volt (1 mw into 1000 ohms). Therefor,
> -20dBu is NOT equal in voltage to -20dBV, nor is pro line level 14 db
> stronger than consumer.
>
> To make things even more confusing, dBv (not to be confused with dBV)
> is the same as dBu. Furthermore, "dB" is kind of a shorthand term that
> could refer to any type of dB, depending on the context. For example,
> you could have +24dBu into your computer which reads 0dBFS and outputs
> 80dB SPL through your monitors. You'll probably look at the peak meter
> and call it a 0dB signal, even though that might not correspond to the
> actual voltage (dBu) or amplitude (SPL).
>
> Anyway, to get to your question, one of the main benefits of using pro
> line level gear is not so much that it "runs hotter" but that pro gear
> is usually balanced...meaning it has a positive and a ground like
> regular unbalanced connections AND a negative used to cancel out noise
> using common mode noise rejection. This allows for longer cable runs,
> reduced noise and a louder signal.

Actually, the opposite on this last point. Balanced lines allows one to
use a lower signal, not a higher (louder) signal for the same level of
noise that would exit in an unbalanced system.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 24, 2005 3:48:54 PM

Archived from groups: rec.audio.pro (More info?)

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:116m8bpr3f26jf2@corp.supernews.com...
> "Doc" wrote ...
>> I've read that professional gear operates with a "hotter" signal. It's
>> not clear to me what exactly this means or why it would make a
>> difference.
>
> Tradition and convention. "Professional" equipment tends to use the signal
> levels (but less so the impedances) common from telephone equipment going
> back the better part of 100 years ago.

At one point +8dBm was very common too.

Julian
Anonymous
April 24, 2005 7:00:01 PM

Archived from groups: rec.audio.pro (More info?)

There's a few simple things here...

A)
How much voltage can
Whatever-Output-Circuit-You-Are-Looking-At-At-The-Moment achieve before it
sounds ugly (You may and -must- define 'ugly'... whether it means it clips
like a demented Marine barber or merely starts "sounding odd" at 6dB below
clipping).

B) with that as a MAXIMUM, when you listen to said circuit with VERY low
level signals, how quiet can you go before noticing the noise floor of the
output circuit?

C) is the above-determined dynamic range adequate for the task-at-hand?


Using dBu isn't practical anymore (like for the last 2 decades!) as
everything's bridged rather than matched and dBu is defined as a power level
into a specified load (I've always considered it as 'referenced to .775v).
The introduction of dBV was an attempt to re-standardise everything to
something that made intuitive sense. Not terribly helpful... And you STILL
haven't defined your desired headroom. In the 60's 30dB or better headroom
above-nominal was considered a good thing and thus circuits were able to do
+30dBu or better and took serious PS rails (with voltage and current
headroom THERE). Anymore, defining a circuit as "+4dB" (why +4 instead of 0?
Because that's how levels worked out with the 1930's meter hookups... MORE
Confusion!) doesn;t tell you whether the output's gonna clip at +10 (which
in essence then redefines it a s a consumer-class) or +30.

In the end TESTING what you HAVE, to see how far it goes, is the only way to
tell you WHAT you have, and then you can decide if it's Good Enough.
And that after all is all we NEED to know.
Anonymous
April 24, 2005 7:01:14 PM

Archived from groups: rec.audio.pro (More info?)

Frame this....



On 4/24/05 7:07 AM, in article 3eudnVgK0fFq4PbfRVn-gw@comcast.com, "Arny
Krueger" <arnyk@hotpop.com> wrote:

> Doc wrote:
>
>> I've read that professional gear operates with a "hotter" signal.
>
> Putting into numbers which some people around here hate:
>
> Consumer gear line level inputs and outputs work with maximum levels
> between 0.1 volt and 2.5 volts. 0.3 volts to 1.5 volt is a more
> common range. 1 volt peak is a common medium signal voltage.
>
> Pro gear works line levels that have maximum levels between about 0.3
> volts (-10) 1.25 (+4) and up to about 10 volts (+22) with a few pieces
> going higher.
>
> Note that with pro gear we actually have common names for these
> various levels. They aren't cast in cement because most gear has
> headroom. That means that a piece of gear specd at +4 will have
> 6-10-18 dB of headroom over 1.25 volts before it clips. IOW it will
> handle like 2.5 or 6.8 or even more than 10 volts without clipping.
>
>> It's not clear to me what exactly this means or why it would make a
>> difference.
>
> Figure that your average piece of pro gear has line-level voltages
> that are about 10 dB more than your average piece of consumer gear. 10
> dB is very noticable. It can cause trouble with clipping or noise.
>
>> Using my Marshall MXL LDC running through a VTB-1 pre, I can record
> an
>> instrument such as a acoustic guitar so that it's either barely
>> audible or more than loud enough to clip. What would be the benefit
>> of a hotter signal?
>
> Depends what you are doing. If what you got works for you, then invoke
> that well-known rule about not fixing things that aren't broke.
>
>> There must be a reason why everyone talks about
>> this, so I must have an incomplete understanding of something.
>
> Hope my numbers help. ;-)
>
>
Anonymous
April 24, 2005 9:09:52 PM

Archived from groups: rec.audio.pro (More info?)

"SSJVCmag" <ten@nozirev.gamnocssj.com> wrote in message
news:BE912CB0.6540%ten@nozirev.gamnocssj.com...

> Using dBu isn't practical anymore (like for the last 2 decades!) as
> everything's bridged rather than matched and dBu is defined as a power
level
> into a specified load (I've always considered it as 'referenced to .775v).

Actually, no; dBu was an attempt to *solve* that problem. You're thinking of
dBm; 0dBm is defined as one milliwatt into an impedance of 600 ohms. That
works out to 0.775V; when manufacturers stopped using 600 ohms as the
standard input impedance, the same voltage (0.775V) was defined as 0dBu,
strictly a voltage-based standard with no reference to the impedances.

Peace,
Paul
Anonymous
April 24, 2005 9:49:23 PM

Archived from groups: rec.audio.pro (More info?)

For those Interested, My Lapse here was forgetting that the terms
Dbu And dBv are identical. Both measure voltage changes referenced to .775v.

Dbu being the earlier one and thus I forgot to go far enough back to dBm.

LECTURE WARNING:

for the completists out there,
while .775 seems a whacked number to decide on as any sort of standard (we
like -1- or -10- or something basic like that) it makes numbers-sense when
you know that the task at hand was passing Real Power down a lonnnnnnng line
for the telephone company and so it defined the nominal level as whatever
would get 1mW onto the line. To determine power delivery in a circuit (think
guitar amps) the load impedance and the voltage determine the power-draw,
with max efficiency being when source and load impedances are matched. The
telco settled on a line-loading impedance of 600ohms (like deciding 8ohms is
the more normal speaker load for amps to work into) and so knowing that 600
was a given, with a decision to reference to a nice numerically-sensible
1mW, the voltage that produced that power level into the 600ohm line happens
to be .775 volts.

Quiz tomorrow





On 4/24/05 1:09 PM, in article
ApQae.108606$cg1.10928@bgtnsc04-news.ops.worldnet.att.net, "Paul Stamler"
<pstamlerhell@pobox.com> wrote:

> dBu was an attempt to *solve* that problem.
>You're thinking of
> dBm; 0dBm is defined as one milliwatt into an impedance of 600 ohms. That
> works out to 0.775V; when manufacturers stopped using 600 ohms as the
> standard input impedance, the same voltage (0.775V) was defined as 0dBu,
> strictly a voltage-based standard with no reference to the impedances.
Anonymous
April 24, 2005 9:56:24 PM

Archived from groups: rec.audio.pro (More info?)

On 4/24/05 1:49 PM, in article BE915464.656C%ten@nozirev.gamnocssj.com,
"SSJVCmag" <ten@nozirev.gamnocssj.com> wrote:

> Dbu And dBv are identical. Both measure voltage changes referenced to .775v.
>
> Dbu being the earlier one and thus I forgot to go far enough back to dBm.

And yes,
I Do know it's supposed to be dBu not Dbu
What I DON;T know is how to type reliably...
Anonymous
April 24, 2005 11:21:09 PM

Archived from groups: rec.audio.pro (More info?)

In article <BE915464.656C%ten@nozirev.gamnocssj.com> ten@nozirev.gamnocssj.com writes:

> For those Interested, My Lapse here was forgetting that the terms
> Dbu And dBv are identical. Both measure voltage changes referenced to .775v.

But only the Teabags use dBv, and they don't much any more except for
the people from over there who will tell you than dBv is the same as
dBu. dBV, on the other hand, is specific, and it's dB relative to 1V.

dBm is dB relative to 1 milliwatt and is a power measurement, not a
voltage measurement. The voltage to pump 1 milliwatt into a given load
impedance varies with the impedance. The impedance is usually implicit
with the technology if it's not specified. In RF, the load impedance
is usually 50 ohms unless otherwise specified. In audio, it's usually
600 ohms unless otherwise specified. But 1 mW is 1 mW no matter what
the frequency and load impedance.

As in John's lecture, we feel more comfortable talking about voltage
than power unless it's real power (the big red electrons rather than
the small blue ones) so that's what gave us dBu and dBV. A 100 watt
amplifier could be specified as being +50 dBm (did I get that right?)
but nobody ever does that.


--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
April 25, 2005 12:34:48 AM

Archived from groups: rec.audio.pro (More info?)

"Jonny Durango" <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote in message
news:9K2dnRRGjaYf6fbfRVn-3Q@comcast.com...

> If you're having a hard time getting good levels on acoustic guitar, it
> may be that your preamp has large "steps" in it's gain stage (my RNP is
> somewhat guilty of this).

Not at all, that was what I was saying. I get plenty of signal/dynamic
range, can easily go from very quiet to far louder than is useful with
negligible to non-existent noise. That's why it's not clear why any stronger
a signal would be of any benefit.
Anonymous
April 25, 2005 12:34:49 AM

Archived from groups: rec.audio.pro (More info?)

"Doc" <docsavage20@xhotmail.com> wrote in message
news:IpTae.16092$44.3345@newsread1.news.atl.earthlink.net...
>
> "Jonny Durango" <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote in
> message
> news:9K2dnRRGjaYf6fbfRVn-3Q@comcast.com...
>
>> If you're having a hard time getting good levels on acoustic guitar, it
>> may be that your preamp has large "steps" in it's gain stage (my RNP is
>> somewhat guilty of this).
>
> Not at all, that was what I was saying. I get plenty of signal/dynamic
> range, can easily go from very quiet to far louder than is useful with
> negligible to non-existent noise. That's why it's not clear why any
> stronger
> a signal would be of any benefit.
>
>

Noise floor is lower.

Period.
Anonymous
April 25, 2005 12:42:23 AM

Archived from groups: rec.audio.pro (More info?)

mergator pimp wrote:
> "Doc" <docsavage20@xhotmail.com> wrote in message
> news:IpTae.16092$44.3345@newsread1.news.atl.earthlink.net...
>
>>"Jonny Durango" <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote in
>>message
>>news:9K2dnRRGjaYf6fbfRVn-3Q@comcast.com...
>>
>>
>>>If you're having a hard time getting good levels on acoustic guitar, it
>>>may be that your preamp has large "steps" in it's gain stage (my RNP is
>>>somewhat guilty of this).
>>
>>Not at all, that was what I was saying. I get plenty of signal/dynamic
>>range, can easily go from very quiet to far louder than is useful with
>>negligible to non-existent noise. That's why it's not clear why any
>>stronger
>>a signal would be of any benefit.
>>
>>
>
>
> Noise floor is lower.
>
> Period.
>
>
>

in short, yeah....again, don't worry about the "strength" of the signal,
it's the balancing and common mode noise rejection that you're after.

Jonny Durango
Anonymous
April 25, 2005 2:05:32 AM

Archived from groups: rec.audio.pro (More info?)

Here are my pointers if they help this thread:
dBU levels are voltages into Unspecified load Z (normally bridging).
(U is the scientific symbol for Voltage.)
A signal generator of, say, 50 Ohms source would have its levels measured in
dBU.
But as soon as a sending line or an amp o/p is terminated with 600 Ohms, its
level is to be measured in dBm (where m =milliWatt).
Noise level at line o/p is invariably more significant to other parties if
an o/p is term'd and measured in dBm and standardised. This assumes source Z
is suitable for 600r load.
dBV are levels referenced to 1V rms. Unless source Z is very low (below 1
Ohm) there is usually a measurable level drop between sending device left
unterm'd to when it is term'd.
dBmO is another type of pro comms level reference....

dBmO
The level of a signal as specified in dBmO, is the level of that signal (in
dBm) as measured at the reference point of the network.

See also

http://www.learntelecoms.com/pdfs/glossary.pdf

http://www.canford.co.uk/techzone/dB-dBu-dBV%20Comparis...

Jim

"SSJVCmag" <ten@nozirev.gamnocssj.com> wrote in message
news:BE912CF9.6541%ten@nozirev.gamnocssj.com...
> Frame this....
>
>
>
> On 4/24/05 7:07 AM, in article 3eudnVgK0fFq4PbfRVn-gw@comcast.com, "Arny
> Krueger" <arnyk@hotpop.com> wrote:
>
>> Doc wrote:
>>
>>> I've read that professional gear operates with a "hotter" signal.
>>
>> Putting into numbers which some people around here hate:
>>
>> Consumer gear line level inputs and outputs work with maximum levels
>> between 0.1 volt and 2.5 volts. 0.3 volts to 1.5 volt is a more
>> common range. 1 volt peak is a common medium signal voltage.
>>
>> Pro gear works line levels that have maximum levels between about 0.3
>> volts (-10) 1.25 (+4) and up to about 10 volts (+22) with a few pieces
>> going higher.
>>
>> Note that with pro gear we actually have common names for these
>> various levels. They aren't cast in cement because most gear has
>> headroom. That means that a piece of gear specd at +4 will have
>> 6-10-18 dB of headroom over 1.25 volts before it clips. IOW it will
>> handle like 2.5 or 6.8 or even more than 10 volts without clipping.
>>
>>> It's not clear to me what exactly this means or why it would make a
>>> difference.
>>
>> Figure that your average piece of pro gear has line-level voltages
>> that are about 10 dB more than your average piece of consumer gear. 10
>> dB is very noticable. It can cause trouble with clipping or noise.
>>
>>> Using my Marshall MXL LDC running through a VTB-1 pre, I can record
>> an
>>> instrument such as a acoustic guitar so that it's either barely
>>> audible or more than loud enough to clip. What would be the benefit
>>> of a hotter signal?
>>
>> Depends what you are doing. If what you got works for you, then invoke
>> that well-known rule about not fixing things that aren't broke.
>>
>>> There must be a reason why everyone talks about
>>> this, so I must have an incomplete understanding of something.
>>
>> Hope my numbers help. ;-)
>>
>>
>
Anonymous
April 25, 2005 2:05:45 AM

Archived from groups: rec.audio.pro (More info?)

Doc <docsavage20@xhotmail.com> wrote:

> Not at all, that was what I was saying. I get plenty of signal/dynamic
> range, can easily go from very quiet to far louder than is useful with
> negligible to non-existent noise. That's why it's not clear why any stronger
> a signal would be of any benefit.

RAP FAQ

www.recaudiopro.net

--
ha
Anonymous
April 25, 2005 7:51:07 AM

Archived from groups: rec.audio.pro (More info?)

Doc wrote:
> "Jonny Durango" <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote in
message
> news:9K2dnRRGjaYf6fbfRVn-3Q@comcast.com...
>
> > If you're having a hard time getting good levels on acoustic
guitar, it
> > may be that your preamp has large "steps" in it's gain stage (my
RNP is
> > somewhat guilty of this).
>
> Not at all, that was what I was saying. I get plenty of
signal/dynamic
> range, can easily go from very quiet to far louder than is useful
with
> negligible to non-existent noise. That's why it's not clear why any
stronger
> a signal would be of any benefit.

It's nice to have standards.
Standards are a good thing, and I wish
there were more accepted standards.
(not just in audio)
Standardizing at a given level into a
defined load simply allows that there
will be a better than even chance of
compatability among devices.
Swapping out one piece of gear in a chain
should NOT mean that the entire gain
structure need to be re-set.

Pin 2 hot ?

rd
Anonymous
April 25, 2005 2:26:25 PM

Archived from groups: rec.audio.pro (More info?)

SSJVCmag wrote:
> For those Interested, My Lapse here was forgetting that the terms
> Dbu And dBv are identical. Both measure voltage changes referenced to
> .775v.
>
> Dbu being the earlier one and thus I forgot to go far enough back to
> dBm.
>
> LECTURE WARNING:
>
> for the completists out there,
> while .775 seems a whacked number to decide on as any sort of
> standard (we like -1- or -10- or something basic like that) it makes
> numbers-sense when you know that the task at hand was passing Real
> Power down a lonnnnnnng line for the telephone company and so it
> defined the nominal level as whatever would get 1mW onto the line. To
> determine power delivery in a circuit (think guitar amps) the load
> impedance and the voltage determine the power-draw, with max
> efficiency being when source and load impedances are matched.

Ahmmm...no. Its pretty bad efficiency when impedances are matched, like
50% wasted in the source.

If the source has a given resistance, then matching the load resistance
to the source results in maximum power transfer, given that one chooses
the load.

However, as far as amp design goes, this criteria is absolutely useless.
One never designs to get the maximum power available dictated from its
internal source resistance. This resistance is often say, 10 mohms,
meaning 100'sKW!

>The
> telco settled on a line-loading impedance of 600ohms (like deciding
> 8ohms is the more normal speaker load for amps to work into) and so
> knowing that 600 was a given, with a decision to reference to a nice
> numerically-sensible 1mW, the voltage that produced that power level
> into the 600ohm line happens to be .775 volts.

One of the reasons for telephone line impedances matching is nothing to
do with power matching at all. It is to prevent "singing", i.e.
oscillations, that occur at 4 wire to 2 wire conversions. The impedance
needs to be matched to obtain cancellation of the loop around signal.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
May 1, 2005 3:47:30 PM

Archived from groups: rec.audio.pro (More info?)

mergator pimp wrote:
> "Doc" <docsavage20@xhotmail.com> wrote in message
> news:IpTae.16092$44.3345@newsread1.news.atl.earthlink.net...
>
>>"Jonny Durango" <jonnydurango1BUSH_FROM_OFFICE@comcast.net> wrote in
>>message
>>news:9K2dnRRGjaYf6fbfRVn-3Q@comcast.com...
>>
>>
>>>If you're having a hard time getting good levels on acoustic guitar, it
>>>may be that your preamp has large "steps" in it's gain stage (my RNP is
>>>somewhat guilty of this).
>>
>>Not at all, that was what I was saying. I get plenty of signal/dynamic
>>range, can easily go from very quiet to far louder than is useful with
>>negligible to non-existent noise. That's why it's not clear why any
>>stronger
>>a signal would be of any benefit.
>>
>>
>
>
> Noise floor is lower.
>
> Period.
>
>
>

A strange paradox, though: if you're in a noisy environment with a loud
source, you'll get less background noise if you use the consumer level
(+4 dbU will make a nearby computer sound like a helicopter!).

Miles
Anonymous
May 1, 2005 11:07:26 PM

Archived from groups: rec.audio.pro (More info?)

On 5/1/05 11:47 AM, in article E5mdnRId1_CsuejfRVn-jw@comcast.com, "Miles
Jackson" <irjapear@comcast.net> wrote:


>> Noise floor is lower.
>>
>> Period.
>>
>>
>>
>
> A strange paradox, though: if you're in a noisy environment with a loud
> source, you'll get less background noise if you use the consumer level
> (+4 dbU will make a nearby computer sound like a helicopter!).
>
> Miles

Like I get a quieter engine if I use a smaller gas tank...?
What ARE you trying to say here?
Anonymous
May 4, 2005 2:39:39 PM

Archived from groups: rec.audio.pro (More info?)

"Miles Jackson" <irjapear@comcast.net> wrote:
>
> A strange paradox, though: if you're in a noisy environment with a
> loud source, you'll get less background noise if you use the consumer
> level (+4 dbU will make a nearby computer sound like a helicopter!).


That's not a paradox, that's an indication that you don't have a handle
on the gain staging in your system.

Feed your recorder a signal at 10dBV, then feed it the same signal at
+4dBm. You'll get an increase in level of almost 12dB. Obviously
EVERYTHING will be louder, including the background noise.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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