Tech Question (50db+50db = ?)

[Chad M Fagin]

Subject says it all

Hypothetically if I have a room with a noise floor of 50db and I add a piece
of equipment that outputs 50db in noise, does my noise floor go up?
If so how much?

This should be a good thread , huh

[Les Cargill]

Chad M Fagin wrote:

> Subject says it all
>
> Hypothetically if I have a room with a noise floor of 50db and I add a piece
> of equipment that outputs 50db in noise, does my noise floor go up?
> If so how much?
>
> This should be a good thread , huh
>
>

SFAI can tell, neither of the two figures shown relate
to a single reference.

Stated as "room schmutz -50dB, equipment noise, -50dB"
(as measured on a meter on the same hunk 'o gear
with kanobs the same for both measurements)
there might be an answer. Use the +3 for power,
+6 for amplitude (or vicety versety) rule.

So the answer is somwhere around 42.

--
Les Cargill

[Les Cargill]

Chad M Fagin wrote:

> Subject says it all
>
> Hypothetically if I have a room with a noise floor of 50db and I add a piece
> of equipment that outputs 50db in noise, does my noise floor go up?
> If so how much?
>
> This should be a good thread , huh
>
>

SFAI can tell, neither of the two figures shown relate
to a single reference.

Stated as "room schmutz -50dB, equipment noise, -50dB"
(as measured on a meter on the same hunk 'o gear
with kanobs the same for both measurements)
there might be an answer. Use the +3 for power,
+6 for amplitude (or vicety versety) rule.

So the answer is somwhere around 42.

--
Les Cargill

[Carey Carlan]

Les Cargill > wrote in
:

> Chad M Fagin wrote:
>
>> Hypothetically if I have a room with a noise floor of 50db and I add
>> a piece of equipment that outputs 50db in noise, does my noise floor
>> go up? If so how much?
>>
>> This should be a good thread , huh

> SFAI can tell, neither of the two figures shown relate
> to a single reference.
>
> Stated as "room schmutz -50dB, equipment noise, -50dB"
> (as measured on a meter on the same hunk 'o gear
> with kanobs the same for both measurements)
> there might be an answer. Use the +3 for power,
> +6 for amplitude (or vicety versety) rule.

Les' answer is correct but may need translation for a newbie.

dB measures the amount of change. You have to say "50 dB louder than
what?". Unlike linear measure (like feet or pounds), dB measures are
logarithmic, so you can't say "50 dB louder than zero". Twice zero is
still zero. You have to start at some positive number.

If both devices are actually making the same amount of noise (i.e. your
room is 50 dB above some reference value and your device makes noise 50 dB
about the SAME reference value) then the power is doubled (3 dB on the
power scale) and the amplitude is doubled (6 dB on the amplitude scale).

[Carey Carlan]

Les Cargill > wrote in
:

> Chad M Fagin wrote:
>
>> Hypothetically if I have a room with a noise floor of 50db and I add
>> a piece of equipment that outputs 50db in noise, does my noise floor
>> go up? If so how much?
>>
>> This should be a good thread , huh

> SFAI can tell, neither of the two figures shown relate
> to a single reference.
>
> Stated as "room schmutz -50dB, equipment noise, -50dB"
> (as measured on a meter on the same hunk 'o gear
> with kanobs the same for both measurements)
> there might be an answer. Use the +3 for power,
> +6 for amplitude (or vicety versety) rule.

Les' answer is correct but may need translation for a newbie.

dB measures the amount of change. You have to say "50 dB louder than
what?". Unlike linear measure (like feet or pounds), dB measures are
logarithmic, so you can't say "50 dB louder than zero". Twice zero is
still zero. You have to start at some positive number.

If both devices are actually making the same amount of noise (i.e. your
room is 50 dB above some reference value and your device makes noise 50 dB
about the SAME reference value) then the power is doubled (3 dB on the
power scale) and the amplitude is doubled (6 dB on the amplitude scale).

[Chris Hornbeck]

On Fri, 21 May 2004 01:59:09 GMT, "Chad M Fagin" >
wrote:

>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>of equipment that outputs 50db in noise, does my noise floor go up?
>If so how much?

Assuming that your 50dB numbers are SPL, then the answer will
vary between 6dB for perfectly corellated in-phase noise, which
adds linearly, to 3dB for uncorellated noise with the same
frequency distributions, which add square root of the sum of the
squares.

Without defining terms, there isn't an answer.

Chris Hornbeck
"the children of marx and coca cola"

[Chris Hornbeck]

On Fri, 21 May 2004 01:59:09 GMT, "Chad M Fagin" >
wrote:

>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>of equipment that outputs 50db in noise, does my noise floor go up?
>If so how much?

Assuming that your 50dB numbers are SPL, then the answer will
vary between 6dB for perfectly corellated in-phase noise, which
adds linearly, to 3dB for uncorellated noise with the same
frequency distributions, which add square root of the sum of the
squares.

Without defining terms, there isn't an answer.

Chris Hornbeck
"the children of marx and coca cola"

[Matt Macchiarolo]

So long and thanks for all the fish.

> So the answer is somwhere around 42.
>
> --
> Les Cargill

[Matt Macchiarolo]

So long and thanks for all the fish.

> So the answer is somwhere around 42.
>
> --
> Les Cargill

[Bob Cain]

Carey Carlan wrote:

> If both devices are actually making the same amount of noise (i.e. your
> room is 50 dB above some reference value and your device makes noise 50 dB
> about the SAME reference value) then the power is doubled (3 dB on the
> power scale) and the amplitude is doubled (6 dB on the amplitude scale).

In amplitude, uncorrelated noise sources of the same level
increase the overall level at the rate 1/sqrt(n) where n is
the number of sources, so two sources would sum to an
increased amplitude of 20*log10(1/sqrt(2)) = 3 dB. To go up
by 6 dB they would have to be highly correlated, in fact
identical.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

[Bob Cain]

Carey Carlan wrote:

> If both devices are actually making the same amount of noise (i.e. your
> room is 50 dB above some reference value and your device makes noise 50 dB
> about the SAME reference value) then the power is doubled (3 dB on the
> power scale) and the amplitude is doubled (6 dB on the amplitude scale).

In amplitude, uncorrelated noise sources of the same level
increase the overall level at the rate 1/sqrt(n) where n is
the number of sources, so two sources would sum to an
increased amplitude of 20*log10(1/sqrt(2)) = 3 dB. To go up
by 6 dB they would have to be highly correlated, in fact
identical.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

[Chad M Fagin]

Thanks guys, this hypothetical situation was referring to SPL level , you
gave me the answers I was looking for

Thanks Again,
Chad
"Bob Cain" > wrote in message
...
>
>
> Carey Carlan wrote:
>
> > If both devices are actually making the same amount of noise (i.e. your
> > room is 50 dB above some reference value and your device makes noise 50
dB
> > about the SAME reference value) then the power is doubled (3 dB on the
> > power scale) and the amplitude is doubled (6 dB on the amplitude scale).
>
> In amplitude, uncorrelated noise sources of the same level
> increase the overall level at the rate 1/sqrt(n) where n is
> the number of sources, so two sources would sum to an
> increased amplitude of 20*log10(1/sqrt(2)) = 3 dB. To go up
> by 6 dB they would have to be highly correlated, in fact
> identical.
>
>
> Bob
> --
>
> "Things should be described as simply as possible, but no
> simpler."
>
> A. Einstein

[Chad M Fagin]

Thanks guys, this hypothetical situation was referring to SPL level , you
gave me the answers I was looking for

Thanks Again,
Chad
"Bob Cain" > wrote in message
...
>
>
> Carey Carlan wrote:
>
> > If both devices are actually making the same amount of noise (i.e. your
> > room is 50 dB above some reference value and your device makes noise 50
dB
> > about the SAME reference value) then the power is doubled (3 dB on the
> > power scale) and the amplitude is doubled (6 dB on the amplitude scale).
>
> In amplitude, uncorrelated noise sources of the same level
> increase the overall level at the rate 1/sqrt(n) where n is
> the number of sources, so two sources would sum to an
> increased amplitude of 20*log10(1/sqrt(2)) = 3 dB. To go up
> by 6 dB they would have to be highly correlated, in fact
> identical.
>
>
> Bob
> --
>
> "Things should be described as simply as possible, but no
> simpler."
>
> A. Einstein

[Richard Kuschel]

>outheast.rr.com>
>
>Subject says it all
>
>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>of equipment that outputs 50db in noise, does my noise floor go up?
>If so how much?
>
>This should be a good thread , huh
>
>
>
>
>
>
>
>

3dB. The total will be 53dB
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

[Richard Kuschel]

>outheast.rr.com>
>
>Subject says it all
>
>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>of equipment that outputs 50db in noise, does my noise floor go up?
>If so how much?
>
>This should be a good thread , huh
>
>
>
>
>
>
>
>

3dB. The total will be 53dB
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

[Harvey Gerst]

(Richard Kuschel) wrote:

>>outheast.rr.com>
>>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>>of equipment that outputs 50db in noise, does my noise floor go up?
>>If so how much?

>3dB. The total will be 53dB
>Richard H. Kuschel

Nope, random noise doesn't sum the same as tones. It'll be something less than
3dB more. I don't remember how much less since I forgot the formula (but at
least, I still remember my name - most of the time).

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

[Harvey Gerst]

(Richard Kuschel) wrote:

>>outheast.rr.com>
>>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>>of equipment that outputs 50db in noise, does my noise floor go up?
>>If so how much?

>3dB. The total will be 53dB
>Richard H. Kuschel

Nope, random noise doesn't sum the same as tones. It'll be something less than
3dB more. I don't remember how much less since I forgot the formula (but at
least, I still remember my name - most of the time).

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

[Les Cargill]

Harvey Gerst wrote:

> (Richard Kuschel) wrote:
>
>
>>>outheast.rr.com>
>>>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>>>of equipment that outputs 50db in noise, does my noise floor go up?
>>>If so how much?
>
>
>>3dB. The total will be 53dB
>>Richard H. Kuschel
>
>
> Nope, random noise doesn't sum the same as tones. It'll be something less than
> 3dB more. I don't remember how much less since I forgot the formula (but at
> least, I still remember my name - most of the time).
>
> Harvey Gerst
> Indian Trail Recording Studio
> http://www.ITRstudio.com/


FWIW, I just did an experiment where I measured the RMS of a
sequence of white noise, then the RMS of two different
(uncorrelated) samples of white noise, and the difference was
very close ( +/- .1 dB ) to 3dB.

I know they were uncorrelated because when the polarity was
inverted on the second sample, I got the same answer for the
RMS of the mixed signals.

This was with CoolEdit 96's "statistics" function, and N-Track
for mixing.

--
Les Cargill

[Les Cargill]

Harvey Gerst wrote:

> (Richard Kuschel) wrote:
>
>
>>>outheast.rr.com>
>>>Hypothetically if I have a room with a noise floor of 50db and I add a piece
>>>of equipment that outputs 50db in noise, does my noise floor go up?
>>>If so how much?
>
>
>>3dB. The total will be 53dB
>>Richard H. Kuschel
>
>
> Nope, random noise doesn't sum the same as tones. It'll be something less than
> 3dB more. I don't remember how much less since I forgot the formula (but at
> least, I still remember my name - most of the time).
>
> Harvey Gerst
> Indian Trail Recording Studio
> http://www.ITRstudio.com/


FWIW, I just did an experiment where I measured the RMS of a
sequence of white noise, then the RMS of two different
(uncorrelated) samples of white noise, and the difference was
very close ( +/- .1 dB ) to 3dB.

I know they were uncorrelated because when the polarity was
inverted on the second sample, I got the same answer for the
RMS of the mixed signals.

This was with CoolEdit 96's "statistics" function, and N-Track
for mixing.

--
Les Cargill