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In article frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>Does anyone know the algorithm that would take a stream of sampled sound
>,shift it 180 deg in phase and spit it back out again?
>ie   sound -> a/d -> dsp to shift phase -> d/a -> sound

This one is so easy that I wonder if it's not part of a homework problem.

			Bruce Karsh
			karsh@sgi.com

In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>Does anyone know the algorithm that would take a stream of sampled sound
>,shift it 180 deg in phase and spit it back out again?

Use an op-amp as as inverter (ie with a gain of -1). One chip, one resistor,
one pot.

cas

How about an op-amp inverting amplifier?

Dev Palmer
wdp@dukee.egr.duke.edu
Duke Electrical Engineering
Room 309 Old Engineering Bldg.
Durham, NC  27706
(919) 660-5282

In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>Does anyone know the algorithm that would take a stream of sampled sound
>,shift it 180 deg in phase and spit it back out again?
>
>ie   sound -> a/d -> dsp to shift phase -> d/a -> sound
>
 
Invert the sign bit

In a recent article by frerichs@adsl (dfRERICHS):

> Does anyone know the algorithm that would take a stream of sampled sound
> ,shift it 180 deg in phase and spit it back out again?
> 

Without giving this much thought :), how about a pair of cascaded Hilbert
transform filters? :)

Mike

In article <7821@nst>, grayt@Software.Mitel.COM (Tom Gray) writes:
> In article <1991May5.233533.18783@ux1.cso.uiuc.edu>
frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
> >Does anyone know the algorithm that would take a stream of sampled
sound
> >,shift it 180 deg in phase and spit it back out again?
> >
> >ie   sound -> a/d -> dsp to shift phase -> d/a -> sound
> >
>  
> Invert the sign bit

Not if it's a 2's complement integer!!

--
-- Michael Purtell --  | "In a hundred years, | There's an Old Irish
Recipe for
mpurtell@iastate.edu   |  we'll all be dead." |   Longevity: Leave the
Table
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Sleepy.
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Thirsty.

In article <1991May5.233533.18783@ux1.cso.uiuc.edu>, frerichs@adsl (dfRERICHS) writes:
> Does anyone know the algorithm that would take a stream of sampled sound
> ,shift it 180 deg in phase and spit it back out again?
> 
> ie   sound -> a/d -> dsp to shift phase -> d/a -> sound
> 
> Thanks
> 
> djf

Its a no-brainer:  just reverse your speaker wires!  Instant 180 degree
phase inversion!    8-]


-- 
  John Gibbons             N8OBJ                     Macedonia, Ohio

           "Welcome My Son, Welcome To The Machine" - Pink Floyd

In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl (dfRERICHS) writes:

   Does anyone know the algorithm that would take a stream of sampled sound
   ,shift it 180 deg in phase and spit it back out again?

   ie   sound -> a/d -> dsp to shift phase -> d/a -> sound

   (it would seem from the nature of the problem that a simplistic analog
    circuit to do this might be possible... some sort of RC net... if anyone
    know if this is possible, PLEASE make it known.)

   Thanks

   djf

I think what you are looking for is the Hilbert Transform.  A
Hilbert Xform shifts the phase of the signal by 90 degrees.  Just
cascade two of them together for a total of 180 degrees.  

There might be an easier way but I can't quite think of it.

Jim
--
James J. Szinger                  Becton Center
jim@fuji.eng.yale.edu             15 Prospect Street
Intelligent Sensors Lab.          Box 2157 Yale Station
Electrical Engineering            New Haven, Connecticut 06520
Yale University                   U.S.A.

In article <5781@media-lab.media.mit.edu.MEDIA.MIT.EDU> cas@media-lab.media.mit.edu (Scud) writes:
>In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>>Does anyone know the algorithm that would take a stream of sampled sound
>>,shift it 180 deg in phase and spit it back out again?
>
>Use an op-amp as as inverter (ie with a gain of -1). One chip, one resistor,
>one pot.
>
>cas
 Inverting is NOT the same as 180 deg phase shift. For a symetric waveform
(eg a sine wave) it looks the same, but with something assymetric what you
will see is the waveform upside-down, which is not the same as shifted 180
deg. Phase shifting moves a waveform along the time axis: it stays the same
way up. Try it on an oscilloscope.

steveq@syd.dms.CSIRO.AU (Stephen Quigg) writes:

% Inverting is NOT the same as 180 deg phase shift.

See?  I'm not the only one who didn't do his homework... :-)

I gotta start reading my ASSPs again!

-- 
Todd Day  |  todd@appmag.com

In article <1991May8.222501.19572@syd.dms.CSIRO.AU> steveq@syd.dms.CSIRO.AU (Stephen Quigg) writes:
>In article <5781@media-lab.media.mit.edu.MEDIA.MIT.EDU> cas@media-lab.media.mit.edu (Scud) writes:
>>In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>>>Does anyone know the algorithm that would take a stream of sampled sound
>>>,shift it 180 deg in phase and spit it back out again?
>>
>>Use an op-amp as as inverter (ie with a gain of -1). 

> Inverting is NOT the same as 180 deg phase shift. For a symetric waveform
>(eg a sine wave) it looks the same, but with something assymetric what you
>will see is the waveform upside-down, which is not the same as shifted 180
>deg. Phase shifting moves a waveform along the time axis: it stays the same
>way up. Try it on an oscilloscope.


	That's wrong.  The inverter is a perfectly good 180 degree
phase shifter, and if you test it at ANY frequency you will see
180 degrees of phase shift; the phase shift versus frequency is
EXACTLY what was asked for.
	Your 'assymmetric waveform' has a lot of Fourier components,
and time-shifting it as you seem to be describing is NOT a
well-defined operation.  You have to find some particular frequency,
derive a time delay from THAT ONE FREQUENCY COMPONENT, and apply
that time delay to get the time-shift, and that is NOT the correct
phase shift for any frequency component except the one you
chose as 'most significant'.

	John Whitmore

In article <1991May8.222501.19572@syd.dms.CSIRO.AU> steveq@syd.dms.CSIRO.AU (Stephen Quigg) writes:
>In article <5781@media-lab.media.mit.edu.MEDIA.MIT.EDU> cas@media-lab.media.mit.edu (Scud) writes:
>>In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
>>>Does anyone know the algorithm that would take a stream of sampled sound
>>>,shift it 180 deg in phase and spit it back out again?
>>
>>Use an op-amp as as inverter (ie with a gain of -1). One chip, one resistor,
>>one pot.
>>
>>cas
> Inverting is NOT the same as 180 deg phase shift. For a symetric waveform
>(eg a sine wave) it looks the same, but with something assymetric what you
>will see is the waveform upside-down, which is not the same as shifted 180
>deg. Phase shifting moves a waveform along the time axis: it stays the same
>way up. Try it on an oscilloscope.



Are we talking about phase shifts or time shifts?  
Phase Shift:  Since the signal can be represented as a sum (or integral) of
complex exponetials, phase shifting can be done by simply multiplying the whole
sum (integral) by exp(  i*p ), where p is the value of the phase shift. This
can be visualized by rotating a vector (our signal) by 180 degrees in the 
complex plane. Since a phase shift of pi (180 degrees) for each component of 
the Fourier series gives that same component multiplied by -1 (e(i*180) = -1), 
the sum of the phase shifted (180 degrees) components gives the original signal
multiplied by -1.  So phase shifting by 180 degrees IS inverting.  This is
why signals that are 180 degrees out of phase are said to cancel eachother out

Time Shift:  A time shift is equivalent to phase shifting each component of
the signal by its frequency times the value of the time shift, not simply 
phase shifting each frequency component by the same phase. This is NOT 
the same thing as performing a simple phase shift on the entire signal.  (It
just happens that for a signal composed of a single frequency (a sine wave), 
a time shift of half the period is equivalent to a phase shift of 180 degrees)

As I understand it, a phase shift by 180 degrees IS inversion.
If I am not using the conventional definitions of the terms "phase shift" and 
"time shift", please let me know.
 






















-- 
-------------------------------------------------------------------------------
jsorenso@thesis1.med.uth.tmc.edu |
				 |
				 |

>> Inverting is NOT the same as 180 deg phase shift. For a symetric waveform
>>(eg a sine wave) it looks the same, but with something assymetric what you
>>will see is the waveform upside-down, which is not the same as shifted 180
>>deg. Phase shifting moves a waveform along the time axis: it stays the same
>>way up. Try it on an oscilloscope.

In article <1991May10.003817.5593@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes:

>	That's wrong.  The inverter is a perfectly good 180 degree
>phase shifter, and if you test it at ANY frequency you will see
>180 degrees of phase shift; the phase shift versus frequency is
>EXACTLY what was asked for.
>	Your 'assymmetric waveform' has a lot of Fourier components,
>and time-shifting it as you seem to be describing is NOT a
>well-defined operation.  You have to find some particular frequency,
>derive a time delay from THAT ONE FREQUENCY COMPONENT, and apply
>that time delay to get the time-shift, and that is NOT the correct
>phase shift for any frequency component except the one you
>chose as 'most significant'.
>
>	John Whitmore


Sorry, John.  I usually don't butt into other people's business here, but
you really are dead wrong.  The phase shift described above is indeed 
correct.  Since any periodic function is always measured against time, 
shifting the function's phase is also a time-related operation.  

In specific response to your article, frequency and Fourier components
have nothing to do with phase shifting.  The shift of a phase, in degrees,
can be expressed by:

dt
-- x 360
L

where:  dt is the shift of the function
        L is the wavelength of the function

Diagramatically, the following example shows the difference 
of a sawtooth wave shifted by 180 degrees, and an inverted sawtooth wave.

      .      .      .      .
     /|     /|     /|     /|
    / |    / |    / |    / |
   /  |   /  |   /  |   /  |
  /   |  /   |  /   |  /   |
 /    | /    | /    | /    |
/     |/     |/     |/     |          Normal sawtooth wave


         .      .      .      .
        /|     /|     /|     /|
       / |    / |    / |    / |
      /  |   /  |   /  |   /  |
     /   |  /   |  /   |  /   |
    /    | /    | /    | /    |
   /     |/     |/     |/     |       Shifted sawtooth wave


\     |\     |\     |\     |
 \    | \    | \    | \    |
  \   |  \   |  \   |  \   |
   \  |   \  |   \  |   \  |
    \ |    \ |    \ |    \ |
     \|     \|     \|     \|
      `      `      `      `         Inverted sawtooth wave
============================================================================
________
|\     /  Alex McPhail
| \   /
|  \ /    mail to mcphail@dataco              
|---X     (uunet!mitel!melair!dataco!mcphail)
|  / \
| /   \   "Wwwwwhat is the air speed of an average swallow?"
|/_____\   
  Alex


 

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