real valued impulse response

On 8/15/14 3:51 PM, julius wrote:
> On Friday, August 15, 2014 9:58:21 AM UTC-4, robert bristow-johnson wrote:
>> Digital VoltMeter
>>
>> like you place the two probes on two different nodes to measure the
>> voltage between them and it reads out "4.89 + j*2.01 volts".
>
> I don't often need a volt meter, but when I do I prefer somebody else do the measurement for me ;-).
>
>>
>> (my point is that "imaginary-valued voltages are imaginary", but inside
>> the mind of a computer there is nothing stopping us from representing a
>> complex-valued quantity.  the "baseband-equivalent" is an *equivalent*
>> in a representative sense, not the *actual*.)
>>
>> later.
>>
>
> Not sure what you're getting at, but I believe Greg Berchin has the answer.

it's about the same as what i'm getting at.  but i think Greg's answer 
needs one more salient word:

On 8/15/14 11:00 AM, Greg Berchin wrote (virtually):
>
>
> That's the key: we can take two *real* signals, define one of them to be
> the real part of a complex signal and the other to be the imaginary part,
> and analyze accordingly.

and that's my point.  in reality, we have *real* signals, but in our 
minds (or in the mind of the computer) we can construct, out of real 
signals, mathematical quantities we *label* as "complex" and apply these 
mathematical rules of complex arithmetic to these quantities.

L8r,

-- 

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

On Fri, 15 Aug 2014 03:15:39 -0500, "SBR123" <100967@dsprelated>
wrote:

>Hello,
>
>Books describing LTI systems often make reference to "real valued impulse
>response". I am little confused here ... what type of practical systems
>would have "complex values impulse response" vis-a-vis "real valued impulse
>response"
>
>Thank you 

Hi SBR123,
   I'm studying FIR digital filters whose 
coefficients are complex-valued.  In I/Q 
systems, as Eric said, where we're interested 
in the instantaneous phase of a signal, then 
complex-coefficient digital filters come in 
handy.  The impulse responses of such filters 
are complex-valued sequences.

[-Rick-]

Rick Lyons <R.Lyons@_bogus_ieee.org> wrote:

(snip)

> Hi SBR123,
>   I'm studying FIR digital filters whose 
> coefficients are complex-valued.  In I/Q 
> systems, as Eric said, where we're interested 
> in the instantaneous phase of a signal, then 
> complex-coefficient digital filters come in 
> handy.  The impulse responses of such filters 
> are complex-valued sequences.

We haven't heard from Jerry lately, but he used to comment on
complex values of physical quantities.  For one, he doesn't
know any voltmeters that read imaginary volts.

In some cases, complex values are used for our convenience,
such as phasors, where the actual physical value is the real
part. If we were better with our trig. identities, then we
wouldn't see a need for complex values.

But some quantities are naturally complex, such as
index of refraction. As a quantity that goes in an exponent,
and where both the real and imaginary parts have physical
significance, it seems reasonable to me to say that it is
complex, instead of considering it is two separate physical
real values. 

In the case of FIR filters, it seems to me that one has
to ask, again, if it is physical or just for the convenience
of humans?  Is it really different than two separate filters,
for the real and imaginary parts?  (I am not trying to claim
either way, just wondering.)

-- glen

On Fri, 22 Aug 2014 18:35:42 +0000 (UTC), glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

>Rick Lyons <R.Lyons@_bogus_ieee.org> wrote:
>
>(snip)
>
>> Hi SBR123,
>>   I'm studying FIR digital filters whose 
>> coefficients are complex-valued.  In I/Q 
>> systems, as Eric said, where we're interested 
>> in the instantaneous phase of a signal, then 
>> complex-coefficient digital filters come in 
>> handy.  The impulse responses of such filters 
>> are complex-valued sequences.
>
>We haven't heard from Jerry lately, but he used to comment on
>complex values of physical quantities.  For one, he doesn't
>know any voltmeters that read imaginary volts.
>
>In some cases, complex values are used for our convenience,
>such as phasors, where the actual physical value is the real
>part. If we were better with our trig. identities, then we
>wouldn't see a need for complex values.
>
>But some quantities are naturally complex, such as
>index of refraction. As a quantity that goes in an exponent,
>and where both the real and imaginary parts have physical
>significance, it seems reasonable to me to say that it is
>complex, instead of considering it is two separate physical
>real values. 
>
>In the case of FIR filters, it seems to me that one has
>to ask, again, if it is physical or just for the convenience
>of humans?  Is it really different than two separate filters,
>for the real and imaginary parts?  (I am not trying to claim
>either way, just wondering.)
>
>-- glen

Hi glen,
   you ask a heck of a good question, ...one I've pondered 
for some time now.  

I'm beginning to agree with the 19th century German 
mathematician Leopold Kronecker, a pioneer in the field of 
number theory.  He believed "Die ganzen Zahlen hat der liebe 
Gott gemacht, alles andere ist Menschenwerk." ("Natural 
numbers were made by our dear God, all else is the work of men.")

[-Rick-]

glen herrmannsfeldt <gah@ugcs.caltech.edu> writes:

> Rick Lyons <R.Lyons@_bogus_ieee.org> wrote:
>
> (snip)
>
>> Hi SBR123,
>>   I'm studying FIR digital filters whose 
>> coefficients are complex-valued.  In I/Q 
>> systems, as Eric said, where we're interested 
>> in the instantaneous phase of a signal, then 
>> complex-coefficient digital filters come in 
>> handy.  The impulse responses of such filters 
>> are complex-valued sequences.
>
> We haven't heard from Jerry lately, but he used to comment on
> complex values of physical quantities.  For one, he doesn't
> know any voltmeters that read imaginary volts.
>
> In some cases, complex values are used for our convenience,
> such as phasors, where the actual physical value is the real
> part. If we were better with our trig. identities, then we
> wouldn't see a need for complex values.
>
> But some quantities are naturally complex, such as
> index of refraction. As a quantity that goes in an exponent,
> and where both the real and imaginary parts have physical
> significance, it seems reasonable to me to say that it is
> complex, instead of considering it is two separate physical
> real values. 
>
> In the case of FIR filters, it seems to me that one has
> to ask, again, if it is physical or just for the convenience
> of humans?  Is it really different than two separate filters,
> for the real and imaginary parts?  (I am not trying to claim
> either way, just wondering.)

Again (as in the past) I'd like to proffer the algebraic view that the
complex numbers (the field of complex numbers) really is a different
"beast" than the real numbers (the field of real numbers), whether or
not complex numbers are something you can feel, touch, measure, etc. in
reality. It is a "thing" that exists. It is like asking if "love"
exists... (But if it does, it stinks, according to the J. Guiles
Band...)
-- 
Randy Yates
Digital Signal Labs
http://www.digitalsignallabs.com

Randy Yates <yates@digitalsignallabs.com> wrote:

(snip, I wrote)

>> We haven't heard from Jerry lately, but he used to comment on
>> complex values of physical quantities.  For one, he doesn't
>> know any voltmeters that read imaginary volts.

>> In some cases, complex values are used for our convenience,
>> such as phasors, where the actual physical value is the real
>> part. If we were better with our trig. identities, then we
>> wouldn't see a need for complex values.

(snip)

> Again (as in the past) I'd like to proffer the algebraic view that the
> complex numbers (the field of complex numbers) really is a different
> "beast" than the real numbers (the field of real numbers), whether or
> not complex numbers are something you can feel, touch, measure, etc. in
> reality. It is a "thing" that exists. It is like asking if "love"
> exists... (But if it does, it stinks, according to the J. Guiles
> Band...)

When you touch something, it is the wave function of the electrons
in your finger interacting with the electrons in the object you
are touching.  Pauli exclusion keeps them from overlapping.

Who believes that wave functions are complex, and who that it should
be two separate real functions?  Remember, unlike phasors and voltages,
it is the absolute square of the wave function that gives the
probability density.

-- glen

On Mon, 25 Aug 2014 10:21:11 -0400, Randy Yates
<yates@digitalsignallabs.com> wrote:

   [Snipped by Lyons]
>
>Again (as in the past) I'd like to proffer the algebraic view that the
>complex numbers (the field of complex numbers) really is a different
>"beast" than the real numbers (the field of real numbers), whether or
>not complex numbers are something you can feel, touch, measure, etc. in
>reality. It is a "thing" that exists. It is like asking if "love"
>exists... (But if it does, it stinks, according to the J. Guiles
>Band...)

   Come live with me, and be my Love;
   and we will all the pleasures prove.
           --Christopher Marlowe (1564-1593)  

[-Rick-]

On Mon, 25 Aug 2014 20:43:20 +0000 (UTC), glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

   [Snipped by Lyons]
>
>When you touch something, it is the wave function of the electrons
>in your finger interacting with the electrons in the object you
>are touching.  Pauli exclusion keeps them from overlapping.
>
>Who believes that wave functions are complex, and who that it should
>be two separate real functions?  Remember, unlike phasors and voltages,
>it is the absolute square of the wave function that gives the
>probability density.
>
>-- glen

Hi glen,
   It's sounds like you may be a physicist, or at 
least have a strong background in physics.

If so, I have a seemingly super-silly question 
for you.  Do modern physicists know what is 
an electron?

For example, if I tell my brother that electrons 
from his car battery flow through the starter motor 
and make the car engine start turning, and if he 
asks me, "What are electrons?", what should I say?

Thanks,
[-Rick-]

On Mon, 25 Aug 2014 19:53:21 -0700
Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> On Mon, 25 Aug 2014 20:43:20 +0000 (UTC), glen herrmannsfeldt
> <gah@ugcs.caltech.edu> wrote:
> 
>    [Snipped by Lyons]
> >
> >When you touch something, it is the wave function of the electrons
> >in your finger interacting with the electrons in the object you
> >are touching.  Pauli exclusion keeps them from overlapping.
> >
> >Who believes that wave functions are complex, and who that it should
> >be two separate real functions?  Remember, unlike phasors and voltages,
> >it is the absolute square of the wave function that gives the
> >probability density.
> >
> >-- glen
> 
> Hi glen,
>    It's sounds like you may be a physicist, or at 
> least have a strong background in physics.
> 
> If so, I have a seemingly super-silly question 
> for you.  Do modern physicists know what is 
> an electron?
> 
> For example, if I tell my brother that electrons 
> from his car battery flow through the starter motor 
> and make the car engine start turning, and if he 
> asks me, "What are electrons?", what should I say?
> 
> Thanks,
> [-Rick-]
> 

Little pieces of electricity.  That is a statement that, while being
almost entirely wrong, conveys everything that you actually wanted to
say.

-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.

On Tuesday, August 26, 2014 12:32:12 PM UTC-4, Rob Gaddi wrote:
> On Mon, 25 Aug 2014 19:53:21 -0700
> 
> Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
> 
> 
> 
> > On Mon, 25 Aug 2014 20:43:20 +0000 (UTC), glen herrmannsfeldt
> 
> > <gah@ugcs.caltech.edu> wrote:
> 
> > 
> 
> >    [Snipped by Lyons]
> 
> > >
> 
> > >When you touch something, it is the wave function of the electrons
> 
> > >in your finger interacting with the electrons in the object you
> 
> > >are touching.  Pauli exclusion keeps them from overlapping.
> 
> > >
> 
> > >Who believes that wave functions are complex, and who that it should
> 
> > >be two separate real functions?  Remember, unlike phasors and voltages,
> 
> > >it is the absolute square of the wave function that gives the
> 
> > >probability density.
> 
> > >
> 
> > >-- glen
> 
> > 
> 
> > Hi glen,
> 
> >    It's sounds like you may be a physicist, or at 
> 
> > least have a strong background in physics.
> 
> > 
> 
> > If so, I have a seemingly super-silly question 
> 
> > for you.  Do modern physicists know what is 
> 
> > an electron?
> 
> > 
> 
> > For example, if I tell my brother that electrons 
> 
> > from his car battery flow through the starter motor 
> 
> > and make the car engine start turning, and if he 
> 
> > asks me, "What are electrons?", what should I say?
> 
> > 
> 
> > Thanks,
> 
> > [-Rick-]
> 
> > 
> 
> 
> 
> Little pieces of electricity.  That is a statement that, while being
> 
> almost entirely wrong, conveys everything that you actually wanted to
> 
> say.
> 
> 
regarding the physicality of complex numbers....  if you replace the word  "complex" with "2 dimensional"  then it doesn't seem so mysterious..

In fact I do have an oscope that will display a "complex" or 2 dimensional signal,, I simply connect the 2 wires to ch1 and ch2 and put the ocsope in XY mode.

Mark