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Subtract audio from noise

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Edward Lang

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang
 
S

Stanislaw Flatto

Jan 1, 1970
0
Edward said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang
Last century it was done by CQ-DX'ers by "properly" cleaning ears.
Not sure what is the "new, improved, updated...." formula for new
millenium. A ticket to La Scala maybe?

Have fun

Stanislaw.
 
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martin griffith

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang
It can't really be done, in the analogue domain


martin
 
A

Ancient_Hacker

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang

What do you mean "subtract"? In the mathematical sense, point by
point?

There's not much point in doing so, as audio generally has undefined
and irrelevant phase.

Which means it makes little difference if you subtract or add.

And if you add, well addition is commutative, so you're adding noise
to audio, which you can do with two resistors.
 
C

Charles

Jan 1, 1970
0
Edward Lang said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

A phase inverted signal can be used in RF communication when two antennas
are available. However, I think that's limited to a specific noise source
(lightning, e.g.) ... not white noise.
 
P

Phil Allison

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.


** Do your own Google on " audio noise reduction ".

Stop posting trolls.



....... Phil
 
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Robert Baer

Jan 1, 1970
0
Edward said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang
There is a *MUCH* simpler way to generate noise...
 
R

Rich Grise

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

By "subtract", do you mean "extract"? In that case, you're out of my
league; but if you really mean "subtract", then just a subtractor circuit.

Good Luck!
Rich
 
W

whit3rd

Jan 1, 1970
0
What would be the simplest analog (not [DSP]) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Filtering, of course. Select the parts of the bandwidth that
carry the largest voice/music information, and attenuate everything
else.

Or if it was the noise you wanted, attenuate the voice/music.

There are other answers for SIMPLE audio signals, which involve
making a model of the audio signal (if it's repetitive or otherwise
predictable, this can work). For a sine wave, for instance,
a phase-locked loop can reproduce the signal even after adding
LOTS of noise. And Shannon's Theorem (on information content
of noisy signals) tells you that it won't be possible to remove
any signal of more complexity than the information, after noise
is taken into account, of the signal+noise.
 
E

Eeyore

Jan 1, 1970
0
Edward said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

To *subtract* the audio ? You mean you just want the noise signal ?

Most ppl want to subtract the noise from the audio.

Graham
 
A

Adrian Tuddenham

Jan 1, 1970
0
Edward Lang said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Why do you need to subtract the audio? What is special about the white
noise you are going to finish up with?

Most people want to* extract* audio from white noise.
 
M

mpm

Jan 1, 1970
0
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang

I'll have to refresh myself on the spectrum distribution of "white"
noise, but my first thought would be to truncate everything above
say... 10kHz. That should get rid of a bunch of it, albeit along
with the high end desired audio signal as well.

Are you building hardware, or just need the job done?
There are several PC-based software applications that can do this, if
that approach would work for whatever you are doing. Cool Edit Pro
(Now known by some other name since Adobe bought them) comes to mind.

But I agree with the other poster, this really can't be done (to my
knowledge) without digital sampling.

-mpm
 
A

Al

Jan 1, 1970
0
Edward Lang said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang

If your are recording, say a choir, and want to remove the noise from
the audience, do this. Point one microphone at the audience and one at
the choir. Invert the signal from the audience and add it to the one
from the choir. Adust the amplitude of the audience microphone so that
it just cancles the audience sound from the choir microphone.

Of course, you may want to use multiple microphones and point them to
maximize your cancellation.

Al
 
E

Eeyore

Jan 1, 1970
0
Al said:
If your are recording, say a choir, and want to remove the noise from
the audience, do this. Point one microphone at the audience and one at
the choir. Invert the signal from the audience and add it to the one
from the choir. Adust the amplitude of the audience microphone so that
it just cancles the audience sound from the choir microphone.

It won't I'm afraid. There will be some cancellation but it'll be far from
complete as the 2 mics won't pick up the 'audience' in an identical manner.

Graham
 
J

john jardine

Jan 1, 1970
0
Edward Lang said:
What would be the simplest analog (not DSDP) way to subtract a complex
audio signal, such as voice or music, from broadband white noise?

Thank you for any advice.

Ed Lang

Normally it would be a opamp wired as a difference amp. But the question is
interesting in that it would imply that white noise intrinsically contains
all the sounds ever produced since the universe began, or liable to be
produced till the end of time.
If this is the case, then subtracting the particular audio signal from this
cacophony will leave noise still containing an infinity of audio signals but
minus 1 of them.
That is, it'll still be white noise :)
 
D

Don Bowey

Jan 1, 1970
0
Normally it would be a opamp wired as a difference amp. But the question is
interesting in that it would imply that white noise intrinsically contains
all the sounds ever produced since the universe began, or liable to be
produced till the end of time.
If this is the case, then subtracting the particular audio signal from this
cacophony will leave noise still containing an infinity of audio signals but
minus 1 of them.
That is, it'll still be white noise :)
But if the white noise is present in real time - not a recording - then it
is possible to receive the noise on a clear frequency, amplify it, invert it
and sum it to leave the wanted signal. It is done effectively in better
communications receivers.
 
A

Ancient_Hacker

Jan 1, 1970
0
If your are recording, say a choir, and want to remove the noise from
the audience, do this. Point one microphone at the audience and one at
the choir. Invert the signal from the audience and add it to the one
from the choir. Adust the amplitude of the audience microphone so that
it just cancles the audience sound from the choir microphone.

Well, it does, in a simpleminded theoretical sense.

But in the real world sound and microphones have wildly varying
frequency response and phase, which makes this method worse than
useless.
 
A

Ancient_Hacker

Jan 1, 1970
0
But if the white noise is present in real time - not a recording - then it
is possible to receive the noise on a clear frequency, amplify it, invert it
and sum it to leave the wanted signal.


Ah, no.
Noise by definition is not predictable. The noise at 1000KHz does
not correlate well with the noise at 1001KHz.
Even if it did, you'd need two receivers with impossibly matched
frequency, bandwidth, and phase response.
It is done effectively in better communications receivers.


There are "Noise blankers", which work great, but only for your basic
Harley motorcycle spark plug impulse noise.
Which isnt really random noise, but has a very regular and
predictable structure. That's why it's possible to do.
 
D

Don Bowey

Jan 1, 1970
0
Ah, no.
Noise by definition is not predictable. The noise at 1000KHz does
not correlate well with the noise at 1001KHz.
Even if it did, you'd need two receivers with impossibly matched
frequency, bandwidth, and phase response.



There are "Noise blankers", which work great, but only for your basic
Harley motorcycle spark plug impulse noise.
Which isnt really random noise, but has a very regular and
predictable structure. That's why it's possible to do.

Why do you you think a simple detect/invert/sum analog process needs "very
regular and predictably structured noise?"


The ones I've used work well with random noise.
 
J

J.A. Legris

Jan 1, 1970
0
Ah, no.
Noise by definition is not predictable. The noise at 1000KHz does
not correlate well with the noise at 1001KHz.
Even if it did, you'd need two receivers with impossibly matched
frequency, bandwidth, and phase response.


There are "Noise blankers", which work great, but only for your basic
Harley motorcycle spark plug impulse noise.
Which isnt really random noise, but has a very regular and
predictable structure. That's why it's possible to do.

Ah, no:

http://www.bose.com/controller?event=view_product_page_event&product=qc2_headphones_index
 
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