Reply by glen herrmannsfeldt●August 16, 20102010-08-16
Pete Johnston <pdj@n_o_s_p_a_m.blueyonder.co.uk> wrote:
(snip)
> As soon as I hear the word "integral" in the description of
> convolution I'm lost.
> I had no DSP training so I can't ask for my money back I'm afraid.
In the DSP world, use the word "sum" instead of "integral."
> Below is a description of convolution (which I posted Years ago on the Kyma
> site) that is almost completely void of maths but should explain how one
> could write DSP to make it work.
> CONVOLUTION WITHOUT THE MATHS.
> Imagine putting a speaker at the front, and a mic at the back of a large
> hall, and playing a single positive going click (one sample wide (1/44100
> sec)) through the speaker, and then recording the results with the mic. The
> recording will be the impulse response of the hall, speaker and mic setup,
> and will be a representation of how the sound has reached the mic after it
> has bounced around the walls and slowly died away.
Is this a digital (sampled) or analog (continuous, ignoring the grain
in the recording tape) recording?
> Let's say this impulse response lasted four seconds and we put this
> recording into a sample player (with all the notes set to the same original
> pitch); then we could play the sound of the reverb in that hall, but only
> if our sound source was a single click. This doesn�??t seem very useful at
> all.
(snip of the rest of the explanation)
I think your explanation goes digital too early.
Convolution can be described in the continuous (analog) domain,
and then approximated in the digital (sampled) domain.
I presume you still remember cassette (analog) tape. It hasn't
been that many years. If you make an analog recording then you
can delay it by any amount of time.
Well, convolution comes up pretty often in optics. If you start
with a lens and image a single point then you find that the
image is not a single point but is blurred out a little bit.
You can then go through the whole explanation with different
intensity spots, but remember that phase is also important.
Now, consider that you have the spot function for a system
(either optical our audio). Now you want to find the response
for any other input signal. You have to sum over all the spots
that make up the source, an infinite number of them, infinitely
close together. (Just close enough that the width is finite.)
That is what the integral is for, and what your explanation
leaves out.
-- glen
Reply by Pete Johnston●August 16, 20102010-08-16
Hi Guys
I struggle with mathematical descriptions of convolution but that didn't
stop me from writing the algorithm and DSP code for the crossfilter module
in Kyma. This was a system that allowed both live signal and live impulse
inputs and starts to convolve the new impulse almost as soon as it hits the
input .
As soon as I hear the word "integral" in the description of convolution I'm
lost.
I had no DSP training so I can't ask for my money back I'm afraid.
Below is a description of convolution (which I posted Years ago on the Kyma
site) that is almost completely void of maths but should explain how one
could write DSP to make it work.
Pete Johnston
[QUOTE]++++++++++++++++++++++++++
CONVOLUTION WITHOUT THE MATHS.
Imagine putting a speaker at the front, and a mic at the back of a large
hall, and playing a single positive going click (one sample wide (1/44100
sec)) through the speaker, and then recording the results with the mic. The
recording will be the impulse response of the hall, speaker and mic setup,
and will be a representation of how the sound has reached the mic after it
has bounced around the walls and slowly died away.
Let's say this impulse response lasted four seconds and we put this
recording into a sample player (with all the notes set to the same original
pitch); then we could play the sound of the reverb in that hall, but only
if our sound source was a single click. This doesn’t seem very useful at
all.
Now imagine that the source sound was a click at half the level; we
wouldn’t need to go back and record a new impulse, we could just play the
same sample but at half level to hear what the reverb would sound like.
Now if the source was a negative-going click we could just play the whole
sample inverted.
Now what if the source signal was two clicks one second apart with the
first one at full level and the second at half level; then we could play
the sample twice at the two different levels, but we would need a sample
player with a polyphony of at least two, as the first sample will still be
playing when the second (half level) sample starts.
Now if our source signal was ten clicks at different levels and polarities,
we could emulate the reverb with a sample player having a polyphony of ten,
as long as we started the samples at the right time and made sure that
their levels match the clicks.
But who wants to hear the reverb of clicks? What we want is the reverb of
real sound, but real digital sound can be considered as a stream of clicks
(44100 clicks per second if the sample rate was 44.1 khz) that sit next to
each other with no gaps between them.
So if we had a sample player with a polyphony of 44100 and we started up
each poly sample one after the other as if the source clicks now lay next
to each other with no gaps between them, and if we set the level of each
poly sample to be the same levels as each individual sample of an input
source signal, then we could make the reverb of any input signal, as long
as it was no longer than one second. The clicks stop being clicks when they
represent the individual sample steps of an evenly flowing signal.
If we had a sample player with a polyphony of 4 * 44100 (176400) we could
put any signal in with no time limit. This is because after 4 seconds the
first poly sample would have finished playing and would then become
available to be reused for the next incoming click (or sample).
Note that all these 176400 samples will all be playing at the same time
(albeit staggered by one sample each), so you can see how convolution can
be very processor intensive. Although this big big sample player doesn’t
need to play samples at different pitches and the samples being played all
use the same impulse wave form. It does have to have a different level
and/or polarity for each poly sample though.
-- PeteJohnston - 29 Jun 2004
Reply by Tim Wescott●January 24, 20102010-01-24
On Sun, 24 Jan 2010 08:32:53 -0500, Walter Banks wrote:
> Eric Jacobsen wrote:
>
>> It was a concrete basement, the walls were (still) unfinished, and
>> there was a nice, well-defined line of divots in the concrete walls,
>> floor, and ceiling where a DC motor had overrun and essentially
>> detonated. There may have still been pieces of armature embedded deep
>> in the holes, I don't know.
>>
>> I can't imagine an EE degree without the hands-on lab stuff. How do
>> you make people responsible for building stuff safely if they're never
>> allowed to see for themselves what the issues may be?
>
> I had a professor in a motors lab with a fairly large three phase AC
> motor running. He unplugged two phases to reduce the noise so he could
> make some point at the same tine as swinging the ends of the unplugged
> cable around. Everyone expected something was going to happen if the
> ends of the open cables touched, instead he plugged them back in
> swapped. The still spinning motor abruptly reversed, my lingering
> memory 40 years latter was seeing the armature briefly stopped and
> waiting for pieces to come off. It held.
The torque on the stopped rotor would have been about the same as the
torque if the rotor had been stopped -- i.e. it's just normal startup
torque. Further, if I recall my math correctly the torque on the reverse-
spinning motor would actually be less than the startup torque --
induction machines have a torque peak that's generally much closer to
their run speed than to 'stopped'.
--
www.wescottdesign.com
Reply by Walter Banks●January 24, 20102010-01-24
Eric Jacobsen wrote:
> On 1/24/2010 6:32 AM, Walter Banks wrote:
> > The still spinning motor abruptly
> > reversed, my lingering memory 40 years latter was seeing the armature
> > briefly stopped and waiting for pieces to come off. It held.
>
> Probably got hot, though! ;)
I have often thought about the forces at work in that stopped
motor.
w..
--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply by Eric Jacobsen●January 24, 20102010-01-24
On 1/24/2010 6:32 AM, Walter Banks wrote:
>
> Eric Jacobsen wrote:
>
>> It was a concrete basement, the walls were (still) unfinished, and there
>> was a nice, well-defined line of divots in the concrete walls, floor,
>> and ceiling where a DC motor had overrun and essentially detonated.
>> There may have still been pieces of armature embedded deep in the holes,
>> I don't know.
>>
>> I can't imagine an EE degree without the hands-on lab stuff. How do you
>> make people responsible for building stuff safely if they're never
>> allowed to see for themselves what the issues may be?
>
> I had a professor in a motors lab with a fairly large three phase AC
> motor running. He unplugged two phases to reduce the noise
> so he could make some point at the same tine as swinging the ends
> of the unplugged cable around. Everyone expected something was
> going to happen if the ends of the open cables touched, instead
> he plugged them back in swapped. The still spinning motor abruptly
> reversed, my lingering memory 40 years latter was seeing the armature
> briefly stopped and waiting for pieces to come off. It held.
>
> w..
Probably got hot, though! ;)
--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
Reply by Walter Banks●January 24, 20102010-01-24
Eric Jacobsen wrote:
> It was a concrete basement, the walls were (still) unfinished, and there
> was a nice, well-defined line of divots in the concrete walls, floor,
> and ceiling where a DC motor had overrun and essentially detonated.
> There may have still been pieces of armature embedded deep in the holes,
> I don't know.
>
> I can't imagine an EE degree without the hands-on lab stuff. How do you
> make people responsible for building stuff safely if they're never
> allowed to see for themselves what the issues may be?
I had a professor in a motors lab with a fairly large three phase AC
motor running. He unplugged two phases to reduce the noise
so he could make some point at the same tine as swinging the ends
of the unplugged cable around. Everyone expected something was
going to happen if the ends of the open cables touched, instead
he plugged them back in swapped. The still spinning motor abruptly
reversed, my lingering memory 40 years latter was seeing the armature
briefly stopped and waiting for pieces to come off. It held.
w..
--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply by JCH●January 7, 20102010-01-07
"brent" <bulegoge@columbus.rr.com> schrieb im Newsbeitrag
news:211f8ac2-4c8b-4fc8-b2b0-c7aef7bf7779@z40g2000vba.googlegroups.com...
> On Dec 27, 2:31 pm, Tim Wescott <t...@seemywebsite.com> wrote:
>
>> Convolution is _not_ the way that real systems in the real world respond
>> to stimuli of any sort. Convolution is just a _mathematical operation_
>> that _approximates_ what real systems do. Sometimes it even does it
>> well.
>>
>
> I have read your thoughts on non-linear systems a couple of times. I
> see what you are saying, but a good understanding of the ideal linear
> system is first required (not an insignificant hurdle)
>
>
>
>> All real systems are nonlinear. The convolution operation is one way to
>> implement a linear model of a system. Thus, the convolution operation
>> does not model any real system with 100% accuracy. As a model, the
>> convolution operation is only as good as the fit between its bedrock
>> assumption of linearity and the system's actual conformity to linear
>> behavior.
>
> In the end, nothing can be modeled with absolute certainty. In the
> end, statistical processes are going to need to be applied. But that
> does not take away from the absolute need for good modeling. Part of
> the engineers job is to determine which model to use.
> On 2010-01-04 11:39:20 -0400, Chris Bore <chris.bore@gmail.com> said:
>
>> On Jan 3, 5:31 pm, Jerry Avins <j...@ieee.org> wrote:
>>> Chris Bore wrote:
>>>> On Jan 3, 2:27 am, Jerry Avins <j...@ieee.org> wrote:
>>>>> Chris Bore wrote:
>>>>>> On Dec 31 2009, 5:49 pm, Randy Yates <ya...@ieee.org> wrote:
>>>>>>> Jerry Avins <j...@ieee.org> writes:
>>>>>>>> Randy Yates wrote:
>>>>>>>>> Jerry Avins <j...@ieee.org> writes:
>>>>>>>>>> [...]
>>>>>>>>>> Relying on a large brittle flange extending out from a stress rai
>> ser
>>>>>>>>>> (abrupt change in section) is an engineering sin you wouldn't com
>> mit.
>>>>>>>>> So when you asked the question, "Why are manhole covers round?", y
>> ou
>>>>>>>>> expected the answer to be based on such knowledge of materials?
>>>>>>>> The expected answer is "So they don't fall through." Knowledge of
>>>>>>>> materials is needed only to deal with nitpicking. :-)
>>>>>>>> This was dealt with here before.
>>>>>>> I don't think it has yet been dealt with properly until now. See my
>>>>>>> recent (like, 2 minutes ago) post to Muzaffer Kal.
>>>>>>> --
>>>>>>> Randy Yates % "She has an
>> IQ of 1001, she has a jumpsuit
>>>>>>> Digital Signal Labs %
>> on, and she's also a telephone."
>>>>>>> mailto://ya...@ieee.org %http://www.digitalsignal
>> labs.com% 'Yours Truly, 2095', *Time*, ELO
>>>>>> Manhole covers here (Surrey, England) are rectangular.
>>>>> How frequently do they need to be fished out of the sewer?
>>>
>>>>> Jerry
>>>>> --
>>>>> Engineering is the art of making what you want from things you can get
>> .- Hide quoted text -
>>>
>>>>> - Show quoted text -
>>>
>>>> They do get stolen, but I never heard of one going down the sewer.
>>>> Maybe the sewer operatives are PhDs...
>>>
>>> Is it possible that when an open hole is seen and the assumption is that
>>> the cover was stolen, the cover fell in instead? Do you know about the
>>> "stolen" Revolutionary War canon on the Princeton University campus?
>>>
>>> Jerry
>>>
>>> There is an old canon on the campus said to be a relic of the Battle of
>>> Monmouth, buried muzzle down, with about a foot and a half projecting
>>> above ground. The weight is estimated to be about a ton. One morning,
>>> there was a large hole in the ground with dirt piled along side it and
>>> no canon in sight. Campus. municipal, and state police combed the campus
>>> looking for clues, wheel tracks, anything. Nothing. Two days later, a
>>> notice appeared on a bulletin board neat campus police office "LOOK
>>> UNDER THE DIRT". The canon had not been moved, merely buried.
>>> --
>>> Engineering is the art of making what you want from things you can get.
>>> ������������������������
>> �������������������������
>> ����������������������- Hide qu
>> oted text -
>>>
>>> - Show quoted text -
>>
>> It would appear that round manhole covers are typical in the USA
>> though not so much in England and Europe. I could find no round ones
>> on a recent tour of the local area that I undertook with the specific
>> intention to research the typical manhole cover shape. Most are
>> rectangles, some are square, some are triangular, but I could not find
>> any round ones. The "can't fall in the hole" argument does not apply
>> here, as most square covers are in fact in two pieces - both
>> triangles. I can only assume that British manhole users are specially
>> trained not to drop the covers down the hole.
>>
>> I have lodged an information request with Surrey County Council to ask
>> how many, if any, manhole covers do fall down the hole. Nobody I know
>> has ever heard of a manhole cover falling fown its hole. The thefts
>> are verified by the cover not being down or near the hole.
>>
>> There is a British Standard for manhole covers (and a European one,
>> but we don't mention that..).
>>
>> I would guess that Surrey manhole covers are rectangular because their
>> design aims to fit in with rectangular paving.
>>
>> By the way, since the USA evidently leads in manhole cover design to
>> avoid the cover falling down the hole, can I ask why US manholes seem
>> to be in the middle of busy roads (ours are usually at the verge)? I
>> would be interested to know how many US manhole users are crushed by
>> passing traffic?
>>
>> Chris
>> =======================
>> Chris Bore
>> BORES Signal Processing
>> www.bores.com
>
> Locally (meaning within walking distance of home) the round one are for
> water
> and sewage and in the middle of the road while rectangular ones are for
> storm
> sewer draining or electircal and at the edge of the road. I had always
> asumed that
> the round ones were that way so there would not be a high stress point from
> the traffic while the others were to allow storm water or personel
> easier access.
> The round ones are much harder to match to the hole beneath then as the
> hole also
> requires special bricks etc etc but they are easier to make good matches
> as big
> lathes are standard insustrial gear. Now and then there will be
> rectangular ones
> in the middle of the road. My impression is they are more prone to
> clatter from
> being slightly off-flat. The not falling in is as a minor advantage but
> not enough
> to cause the middle of the road rectangles to be fixed.
>
> The not falling in is a standard trick question and I have always
> assumed it was
> more an urban legend than actual civil engineerng practice.
I have a few times in my capacity sitting on the board of a sewerage
authority removed and replaced round manhole covers with only a hook and
chain. I had no difficulty managing their substantial weight on my own.
The time that I removed a much lighter rectangular catch-basin grate in
order to retrieve my car keys, I was very lucky to have the assistance
of a passing policeman when putting it back. Maybe "so they can't fall
in" is too simplistic. "So one can be sure they won't fall in and can
therefore manipulate them with ease and tranquility" might be more accurate.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Gordon Sande●January 4, 20102010-01-04
On 2010-01-04 11:39:20 -0400, Chris Bore <chris.bore@gmail.com> said:
> On Jan 3, 5:31�pm, Jerry Avins <j...@ieee.org> wrote:
>> Chris Bore wrote:
>>> On Jan 3, 2:27 am, Jerry Avins <j...@ieee.org> wrote:
>>>> Chris Bore wrote:
>>>>> On Dec 31 2009, 5:49 pm, Randy Yates <ya...@ieee.org> wrote:
>>>>>> Jerry Avins <j...@ieee.org> writes:
>>>>>>> Randy Yates wrote:
>>>>>>>> Jerry Avins <j...@ieee.org> writes:
>>>>>>>>> [...]
>>>>>>>>> Relying on a large brittle flange extending out from a stress rai
> ser
>>>>>>>>> (abrupt change in section) is an engineering sin you wouldn't com
> mit.
>>>>>>>> So when you asked the question, "Why are manhole covers round?", y
> ou
>>>>>>>> expected the answer to be based on such knowledge of materials?
>>>>>>> The expected answer is "So they don't fall through." Knowledge of
>>>>>>> materials is needed only to deal with nitpicking. :-)
>>>>>>> This was dealt with here before.
>>>>>> I don't think it has yet been dealt with properly until now. See my
>>>>>> recent (like, 2 minutes ago) post to Muzaffer Kal.
>>>>>> --
>>>>>> Randy Yates � � � � � � � � � � �% "She has an
> IQ of 1001, she has a jumpsuit
>>>>>> Digital Signal Labs � � � � � � �% � � � � �
> �on, and she's also a telephone."
>>>>>> mailto://ya...@ieee.org � � � � �%http://www.digitalsignal
> labs.com%� � � 'Yours Truly, 2095', *Time*, ELO �
>>>>> Manhole covers here (Surrey, England) are rectangular.
>>>> How frequently do they need to be fished out of the sewer?
>>
>>>> Jerry
>>>> --
>>>> Engineering is the art of making what you want from things you can get
> .- Hide quoted text -
>>
>>>> - Show quoted text -
>>
>>> They do get stolen, but I never heard of one going down the sewer.
>>> Maybe the sewer operatives are PhDs...
>>
>> Is it possible that when an open hole is seen and the assumption is that
>> the cover was stolen, the cover fell in instead? Do you know about the
>> "stolen" Revolutionary War canon on the Princeton University campus?
>>
>> Jerry
>>
>> There is an old canon on the campus said to be a relic of the Battle of
>> Monmouth, buried muzzle down, with about a foot and a half projecting
>> above ground. The weight is estimated to be about a ton. One morning,
>> there was a large hole in the ground with dirt piled along side it and
>> no canon in sight. Campus. municipal, and state police combed the campus
>> looking for clues, wheel tracks, anything. Nothing. Two days later, a
>> notice appeared on a bulletin board neat campus police office "LOOK
>> UNDER THE DIRT". The canon had not been moved, merely buried.
>> --
>> Engineering is the art of making what you want from things you can get.
>> ������������������������
> �������������������������
> ����������������������- Hide qu
> oted text -
>>
>> - Show quoted text -
>
> It would appear that round manhole covers are typical in the USA
> though not so much in England and Europe. I could find no round ones
> on a recent tour of the local area that I undertook with the specific
> intention to research the typical manhole cover shape. Most are
> rectangles, some are square, some are triangular, but I could not find
> any round ones. The "can't fall in the hole" argument does not apply
> here, as most square covers are in fact in two pieces - both
> triangles. I can only assume that British manhole users are specially
> trained not to drop the covers down the hole.
>
> I have lodged an information request with Surrey County Council to ask
> how many, if any, manhole covers do fall down the hole. Nobody I know
> has ever heard of a manhole cover falling fown its hole. The thefts
> are verified by the cover not being down or near the hole.
>
> There is a British Standard for manhole covers (and a European one,
> but we don't mention that..).
>
> I would guess that Surrey manhole covers are rectangular because their
> design aims to fit in with rectangular paving.
>
> By the way, since the USA evidently leads in manhole cover design to
> avoid the cover falling down the hole, can I ask why US manholes seem
> to be in the middle of busy roads (ours are usually at the verge)? I
> would be interested to know how many US manhole users are crushed by
> passing traffic?
>
> Chris
> =======================
> Chris Bore
> BORES Signal Processing
> www.bores.com
Locally (meaning within walking distance of home) the round one are for water
and sewage and in the middle of the road while rectangular ones are for storm
sewer draining or electircal and at the edge of the road. I had always
asumed that
the round ones were that way so there would not be a high stress point from
the traffic while the others were to allow storm water or personel
easier access.
The round ones are much harder to match to the hole beneath then as the
hole also
requires special bricks etc etc but they are easier to make good matches as big
lathes are standard insustrial gear. Now and then there will be
rectangular ones
in the middle of the road. My impression is they are more prone to clatter from
being slightly off-flat. The not falling in is as a minor advantage but
not enough
to cause the middle of the road rectangles to be fixed.
The not falling in is a standard trick question and I have always
assumed it was
more an urban legend than actual civil engineerng practice.
Reply by brent●January 3, 20102010-01-03
On Jan 3, 3:29�pm, "invalid" <inva...@invalid.invalid> wrote:
> "brent" <buleg...@columbus.rr.com> wrote in message
>
> news:348ec1e2-dd29-41b3-b771-18366ac0790c@h9g2000yqa.googlegroups.com...
>
> > I think you err in wanting everything to come together in one sitting
> > or reading.
>
> I made no statement to that effect, nor did I express such a wish.