>On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
>> In graphical convolution either the system impulse response h(n) or
the
>> input x(n) is folded/flipped and then slid across the other to
determine
>> the system response y(n). Why is this so? I have reasoned this as
being
>> necessary to align the "present" input to the "present" output of the
>> system response to get the correct system time output. Is this
reasoning
>> valid? None of the several signals and systems texts I have consulted
>> simply enumerate the mechanical steps without any further
clarification.
>
>The best explanation offered so far on comp.dsp is this one:
>
>http://groups.google.no/group/comp.dsp/msg/f99bcd270cc776d8?hl=no&
>
>The convolution sum formula is derived from the most basic
>propertes of an LTI system. If you do that, the flipping
>is one way of interpreting the resulting formula.
>
>Rune
>
Hi Rune,
The convolution example illustrated at the web site suggested by you has
helped in clearing the confusion.
Thanks a lot for your help.
Regards
Azhar
Reply by Jerry Avins●May 2, 20092009-05-02
John wrote:
> On May 2, 2:23 pm, Randy Yates <ya...@ieee.org> wrote:
>> Rune Allnor <all...@tele.ntnu.no> writes:
>>> On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
>>>> In graphical convolution either the system impulse response h(n) or the
>>>> input x(n) is folded/flipped and then slid across the other to determine
>>>> the system response y(n). Why is this so? I have reasoned this as being
>>>> necessary to align the "present" input to the "present" output of the
>>>> system response to get the correct system time output. Is this reasoning
>>>> valid? None of the several signals and systems texts I have consulted
>>>> simply enumerate the mechanical steps without any further clarification.
>>> The best explanation offered so far on comp.dsp is this one:
>>> http://groups.google.no/group/comp.dsp/msg/f99bcd270cc776d8?hl=no&
>> I agree, Rune, that this is the best, and simplest, illustration of
>> convolution I know, and it answers the OP's question nicely.
>>
>> I'll bet Dilip is one of the best college propfessors at any
>> school today, judging from this and the many other helpful
>> and intelligent answers he has provided here in the past.
>> --
>> % Randy Yates % "So now it's getting late,
>> %% Fuquay-Varina, NC % and those who hesitate
>> %%% 919-577-9882 % got no one..."
>> %%%% <ya...@ieee.org> % 'Waterfall', *Face The Music*, ELOhttp://www.digitalsignallabs.com
>
> I concur. He is one of those who makes comp.dsp worthwhile.
One of my minor regrets is that I didn't know he was at Princeton until
he wasn't any more. I would like to have met him in person.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by John●May 2, 20092009-05-02
On May 2, 2:23�pm, Randy Yates <ya...@ieee.org> wrote:
> Rune Allnor <all...@tele.ntnu.no> writes:
> > On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
> >> In graphical convolution either the system impulse response h(n) or the
> >> input x(n) is folded/flipped and then slid across the other to determine
> >> the system response y(n). Why is this so? I have reasoned this as being
> >> necessary to align the "present" input to the "present" output of the
> >> system response to get the correct system time output. Is this reasoning
> >> valid? None of the several signals and systems texts I have consulted
> >> simply enumerate the mechanical steps without any further clarification.
>
> > The best explanation offered so far on comp.dsp is this one:
>
> >http://groups.google.no/group/comp.dsp/msg/f99bcd270cc776d8?hl=no&
>
> I agree, Rune, that this is the best, and simplest, illustration of
> convolution I know, and it answers the OP's question nicely.
>
> I'll bet Dilip is one of the best college propfessors at any
> school today, judging from this and the many other helpful
> and intelligent answers he has provided here in the past.
> --
> % �Randy Yates � � � � � � � � �% "So now it's getting late,
> %% Fuquay-Varina, NC � � � � � �% � �and those who hesitate
> %%% 919-577-9882 � � � � � � � �% � �got no one..."
> %%%% <ya...@ieee.org> � � � � � % 'Waterfall', *Face The Music*, ELOhttp://www.digitalsignallabs.com
I concur. He is one of those who makes comp.dsp worthwhile.
John
Reply by Randy Yates●May 2, 20092009-05-02
Rune Allnor <allnor@tele.ntnu.no> writes:
> On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
>> In graphical convolution either the system impulse response h(n) or the
>> input x(n) is folded/flipped and then slid across the other to determine
>> the system response y(n). Why is this so? I have reasoned this as being
>> necessary to align the "present" input to the "present" output of the
>> system response to get the correct system time output. Is this reasoning
>> valid? None of the several signals and systems texts I have consulted
>> simply enumerate the mechanical steps without any further clarification.
>
> The best explanation offered so far on comp.dsp is this one:
>
> http://groups.google.no/group/comp.dsp/msg/f99bcd270cc776d8?hl=no&
I agree, Rune, that this is the best, and simplest, illustration of
convolution I know, and it answers the OP's question nicely.
I'll bet Dilip is one of the best college propfessors at any
school today, judging from this and the many other helpful
and intelligent answers he has provided here in the past.
--
% Randy Yates % "So now it's getting late,
%% Fuquay-Varina, NC % and those who hesitate
%%% 919-577-9882 % got no one..."
%%%% <yates@ieee.org> % 'Waterfall', *Face The Music*, ELO
http://www.digitalsignallabs.com
Reply by Fred Marshall●May 1, 20092009-05-01
Rune Allnor wrote:
> On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
>> In graphical convolution either the system impulse response h(n) or
>> the input x(n) is folded/flipped and then slid across the other to
>> determine the system response y(n). Why is this so? I have reasoned
>> this as being necessary to align the "present" input to the
>> "present" output of the system response to get the correct system
>> time output. Is this reasoning valid? None of the several signals
>> and systems texts I have consulted simply enumerate the mechanical
>> steps without any further clarification.
>
Here's my take on it:
Start with the impulse response y(t) or the unit sample response y(n) of the
system.
We usually plot these with time or index increasing to the right.
So, the initial part starts on the left.
Now consider a signal. We usually plot signals the same way.
But, when we pass a signal through a system it is the "first part" of the
signal that kicks off the "first part" of the system response.
The point of the convolution is to calculate the output of the system for a
particular signal. Of course this requires using the system response in the
calculation.
So, putting it all together, we need to operate on the first part of the
signal with the first part of the system response and next the "second part"
of the signal on the first part of the system response while operating on
the "second part" of the system response with the first part of the signal
and so on.
If this is clear then the reason for flipping should be clear enough.
You have to butt the beginnings together to start the calculation.
The system doesn't really have a "present" except when there are initial
conditions. Generally the system is considered to be at rest when the input
is applied. Thus whatever state the system takes is due to the signal - so
the system's present state is completely dependent on the present state of
the input and *its* history - the system characteristics affect what the
system state becomes but only due to the input.
It might also help to consider superposition which works very nicely in
linear time-invariant systems:
- first I put in this little signal piece.
- then I put in another little signal piece.
- etc.
the system responds first to one and then the other while still responding
to the first ... and so on. The responses to the two are superimposed.
The graphical method helps to envision how this works I do believe.
Fred
Reply by Rune Allnor●May 1, 20092009-05-01
On 1 Mai, 15:02, "AHSHAH" <azharsha...@yahoo.com> wrote:
> In graphical convolution either the system impulse response h(n) or the
> input x(n) is folded/flipped and then slid across the other to determine
> the system response y(n). Why is this so? I have reasoned this as being
> necessary to align the "present" input to the "present" output of the
> system response to get the correct system time output. Is this reasoning
> valid? None of the several signals and systems texts I have consulted
> simply enumerate the mechanical steps without any further clarification.
The best explanation offered so far on comp.dsp is this one:
http://groups.google.no/group/comp.dsp/msg/f99bcd270cc776d8?hl=no&
The convolution sum formula is derived from the most basic
propertes of an LTI system. If you do that, the flipping
is one way of interpreting the resulting formula.
Rune
Reply by AHSHAH●May 1, 20092009-05-01
In graphical convolution either the system impulse response h(n) or the
input x(n) is folded/flipped and then slid across the other to determine
the system response y(n). Why is this so? I have reasoned this as being
necessary to align the "present" input to the "present" output of the
system response to get the correct system time output. Is this reasoning
valid? None of the several signals and systems texts I have consulted
simply enumerate the mechanical steps without any further clarification.
Can someone please help me with this vexation.
Thanks