Amplitude distortion and phase distortion

[SaMPEI]

In a monodimensional,linear,time-invariant system there is a
relationship between amplitude distortion and phase distortion?if
yes,why?
thanks

 

[The Phantom]

On 18 Jul 2005 13:41:57 -0700, sampei82@gmail.com (SaMPEI) wrote:

In a monodimensional,linear,time-invariant system there is a
relationship between amplitude distortion and phase distortion?if
yes,why?

It is the will of Bode.

Go read "Network Analysis and Feedback Amplifier Design", H. W. Bode

>thanks

 

[Rene Tschaggelar]

SaMPEI wrote:

In a monodimensional,linear,time-invariant system there is a
relationship between amplitude distortion and phase distortion?

The term distortion is not really used in enginerring.
In signal theory, there is the linear transmission
function, which doe not creates harmonics, and there
are the non-linear cases with harmonics.
The linear transmission function relates the amplitude
and phase response of the system to the input signal.
The non-linear cases are not nearly as good covered
with theory as are the linear ones.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[Joseph]

I have read that a Fir filter has linear phase so is amplitude response
hasn't distortion in passband(no oscillation is present):this
affirmation is true?
bye

 

[Charles DH Williams]

In article <1121768441.583843.190820@g44g2000cwa.googlegroups.com>,
"Joseph" <sampei82@gmail.com> wrote:

I have read that a Fir filter has linear phase so is amplitude response
hasn't distortion in passband(no oscillation is present):this
affirmation is true?
bye

Not all FIR filters have a linear phase vs frequency relationship.

If a linear phase vs frequency relationship is required it is
usual to use a FIR.

A filter with a linear linear phase vs frequency relationship
delays a time domain signal without changing its shape. The delayed
signal will be distorted if it has harmonic content that lies outside
the range of frequencies where the linear phase relationship is
true.

Charles

 

[Rene Tschaggelar]

Joseph wrote:

I have read that a Fir filter has linear phase so is amplitude response
hasn't distortion in passband(no oscillation is present):this
affirmation is true?

To start with, get rid of this distortion stuff. Linear
systems do not have distortions, by definition. When
distortion comes in, they are in the nonlinear regime,
eg clipping. This is not covered by the linear theory.

There is amplitude ratio and phase shift. One pair
for each frequency.

A FIR is a forward propagating multiply-add-register
set. It has thus a finit impulse response.
Depending on the coefficient, whatever amplitude
and phase response can be achieved.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[Mark]

homework problem?

Mark

 

[Jon]

By phase distortion, I assume you are referring to a deviation from
linear phase. There is a relationship, but it depends on the transfer
function of the system. For example, an all-pass filter has an output
whose amplitude does not vary with frequency, but its phase shift does.

 

[Jon]

Joseph,
A FIR filter can be made to have linear phase. Any FIR filter whose
coefficents are symmetrical with respect to the center coefficent wil
have linear phase. For example, let A(c) = the coefficient of the
middle sample. Then if A(c-1) = A(c+1), A(c-2) = A(c+2), etc the filter
will have linear phase. All FIRs do not necessarily have linear phase.
No analog system can be made to have linear phase.
Regards,
Kral

 

[Charles DH Williams]

In article <1121785824.705690.78440@g43g2000cwa.googlegroups.com>,
"Jon" <jon.lark@l-3com.com> wrote:

No analog system can be made to have linear phase.

?

Analog low pass Bessel filters can have a good approximation to linear
phase. A piece of transmission line also has excellent linear phase.

C.

 

[Rich Grise]

On Mon, 18 Jul 2005 13:41:57 -0700, SaMPEI wrote:

In a monodimensional,linear,time-invariant system there is a
relationship between amplitude distortion and phase distortion?if
yes,why?

No.

Cheers!
Rich

 

[Adrian Tuddenham]

Rene Tschaggelar <none@none.net> wrote:

Joseph wrote:

I have read that a Fir filter has linear phase so is amplitude response
hasn't distortion in passband(no oscillation is present):this
affirmation is true?

To start with, get rid of this distortion stuff. Linear
systems do not have distortions, by definition.

If you are only talking about waveform distortion, this is true.

The terms 'phase distortion' and 'frequency distortion' (meaning limited
bandwidth) also exist. These days they are less commonly used
expressions, but they do need to be excluded from your definition.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

 

[Ban]

Jon wrote:

Joseph,
A FIR filter can be made to have linear phase. Any FIR filter whose
coefficents are symmetrical with respect to the center coefficent wil
have linear phase. For example, let A(c) = the coefficient of the
middle sample. Then if A(c-1) = A(c+1), A(c-2) = A(c+2), etc the
filter will have linear phase. All FIRs do not necessarily have
linear phase. No analog system can be made to have linear phase.
Regards,
Kral

There seem to be different meanings of 'linear phase' if used by digital and
analog guys respectivly.
In digital is meant a filter without any phase shift (exept a certain
unavoidable constant delay).
An analog guy will understand 'linear phase', that the phase is increasing
linearly with frequency. Unadvertedly this will lead to the same as above, a
constant delay for all frequencies.
The thing is, the digital guy forgets about the delay and is proud that his
filter has no phase change at all. And the analog guy forgets about the
filter and concentrates on the delay...
The analog loves OTOH a *minimum* phase filter. This type is related to the
OP-question, because in the analog world every filter needs a phase change
to perform its function. For a filter of 1st order this will be +90° for a
HP or -90° for a LP at the -3dB points and +/-180° at infinite/zero. A 2nd
order filter has double of these values. Most natural processes (pendulum,
mass/spring etc.) behave as minimum phase systems.
A minimum phase filter has the shortest possible delay. Sometimes a very
important attribute.
We can calculate the phase from the amplitude in a frequency plot for a
minimum phase system, this might be helpful in certain processing
situations.
--
ciao Ban
Bordighera, Italy

 

[Ban]

Ban wrote:

Jon wrote:
Joseph,
A FIR filter can be made to have linear phase. Any FIR filter whose
coefficents are symmetrical with respect to the center coefficent wil
have linear phase. For example, let A(c) = the coefficient of the
middle sample. Then if A(c-1) = A(c+1), A(c-2) = A(c+2), etc the
filter will have linear phase. All FIRs do not necessarily have
linear phase. No analog system can be made to have linear phase.
Regards,
Kral

There seem to be different meanings of 'linear phase' if used by
digital and analog guys respectivly.
In digital is meant a filter without any phase shift (exept a certain
unavoidable constant delay).
An analog guy will understand 'linear phase', that the phase is
increasing linearly with frequency. Unadvertedly this will lead to
the same as above, a constant delay for all frequencies.
The thing is, the digital guy forgets about the delay and is proud
that his filter has no phase change at all. And the analog guy
forgets about the filter and concentrates on the delay...
The analog loves OTOH a *minimum* phase filter. This type is related
to the OP-question, because in the analog world every filter needs a
phase change to perform its function. For a filter of 1st order this
will be +90° for a HP or -90° for a LP at the -3dB points and +/-180°
at infinite/zero. A 2nd order filter has double of these values. Most
natural processes (pendulum, mass/spring etc.) behave as minimum
phase systems. A minimum phase filter has the shortest possible delay.
Sometimes a
very important attribute.
We can calculate the phase from the amplitude in a frequency plot for
a minimum phase system, this might be helpful in certain processing
situations.

a 1st order filter has 45° at the corner frequency and 90° at infinite,
what I wrote was for a second order filter.
sorry

--
ciao Ban
Bordighera, Italy

 

[Poly Chrome]

"Ban" <bansuri@web.de> wrote in message
news:1oSEe.3705$2U1.397379@news3.tin.it...

Jon wrote:
Joseph,
A FIR filter can be made to have linear phase. Any FIR filter whose
coefficents are symmetrical with respect to the center coefficent wil
have linear phase. For example, let A(c) = the coefficient of the
middle sample. Then if A(c-1) = A(c+1), A(c-2) = A(c+2), etc the
filter will have linear phase. All FIRs do not necessarily have
linear phase. No analog system can be made to have linear phase.
Regards,
Kral

There seem to be different meanings of 'linear phase' if used by digital
and
analog guys respectivly.
In digital is meant a filter without any phase shift (exept a certain
unavoidable constant delay).
An analog guy will understand 'linear phase', that the phase is increasing
linearly with frequency. Unadvertedly this will lead to the same as above,
a
constant delay for all frequencies.

check a good filter book.
linear phase = constant delay
delay is the derivative of phase

 

[Ban]

Poly Chrome wrote:

"Ban" <bansuri@web.de> wrote in message
news:1oSEe.3705$2U1.397379@news3.tin.it...
Jon wrote:
Joseph,
A FIR filter can be made to have linear phase. Any FIR filter whose
coefficents are symmetrical with respect to the center coefficent
wil have linear phase. For example, let A(c) = the coefficient of
the middle sample. Then if A(c-1) = A(c+1), A(c-2) = A(c+2), etc the
filter will have linear phase. All FIRs do not necessarily have
linear phase. No analog system can be made to have linear phase.
Regards,
Kral

There seem to be different meanings of 'linear phase' if used by
digital and analog guys respectivly.
In digital is meant a filter without any phase shift (exept a certain
unavoidable constant delay).
An analog guy will understand 'linear phase', that the phase is
increasing linearly with frequency. Unadvertedly this will lead to
the same as above, a constant delay for all frequencies.

check a good filter book.
linear phase = constant delay
delay is the derivative of phase

Yes, exactly what I wrote.
For a digital guy the meaning is not constant delay, but a filter with an
amplitude function without any impact on the phase. This is indeed
impossible in the analog domain.
--
ciao Ban
Bordighera, Italy