Questions about equivalents of audio/video and digital/analog.

On Aug 19, 7:59 pm, Jerry Avins wrote:

Radium wrote:

2. Decreasing the spatial frequency of the images in the video-signal
without low-pass filtering the images or increasing their sizes. An
example of this would be making the sharp areas of an image look
duller without decreasing the "sharpness" setting [an example of low-
pass filtering] on the monitor or increasing the size of the image.
Normally, when the size of an image is decreased, its sharpness
increases [it's like compressing a lower-frequency sound wave into a
higher-frequency one]. Likewise, when the size of an image is
increased, it looks duller [like stretching a higher-frequency sound
wave into a lower-frequency one]. Low-pass filtering simply decreasing
the sharpness of an image while increasing its dull characteristics --
which is what I don't want.

That's a reasonable summary of what you don't want to do. What do you
think you might do instead?

The video-equivalent of changing the 'pitch' of audio recording
without changing the playback speed.

#1 Decreases the rate at which objects in the video move without
decreasing the video's playback speed or eliminating originally-
rapidly-moving objects [such as the rapidly flapping wings]

Something has to give. If the flapping of the wings is slowed, so is the
motion of everything else.

The motion of 'everything else' *is* slowed. However, the playback
speed remains constant.

Repetitive or cyclical motion (such as a ball bouncing, or a wagon
wheel rotating, or a bird-flapping its wings, or an exposed model of a
piston engine operating, or a flag waving in the wind) in the movie
are slowed without lengthening the clip.

#2 Decreases makes a still image less sharp by stretching everything
within the image without increasing the size of the image or
eliminating sharp portions of the original image

Huh?

Sorry that should read "makes a still image less sharp by stretching
everything within the image without increasing the size of the image
or eliminating sharp portions of the original image"

My bad.

Anyways, this is an original pictu
http://www-dse.doc.ic.ac.uk/~nd/surp...ormalimage.jpg

This is how the picture looks after low-pass filtering -- YUK!:

http://www-dse.doc.ic.ac.uk/~nd/surp...ort.lopass.jpg

I don't want low-pass filtering. I simply want all frequencies to be
downshifted similar to decreasing the pitch of audio without slowing
the playback speed. The analogy is lower the frequencies of all
components in the image w/out increasing the size of the image or
doing any low-pass filtering.

http://www-dse.doc.ic.ac.uk/~nd/surp...ab/report.html

Both #1 and #2 are visual-equivalents of decreasing the pitch of a
recorded audio signal without decreasing the audio's playback speed.

Says who? You're reasoning from false analogy again.

How is it false?

On Aug 19, 8:34 pm, "Bob Myers" wrote:

Sampled analog systems are certainly
not very common today (unless you count certain forms of
modulation as "sampling," and in fact there are some very close
parallels there), but the theory remains the same no matter which
form of encoding is used. In any event, you must sample the
original signal at a rate equal to at least twice its bandwidth (actually,
very slightly higher, to avoid a particular degenerate case which
could occur at EXACTLY 2X the bandwidth) in order to preserve
the information in the original and avoid "aliasing."

Is the CCD [Charge Coupled Device] a "sampled analog system"?

Radium wrote:
On Aug 19, 7:59 pm, Jerry Avins wrote:

Radium wrote:

2. Decreasing the spatial frequency of the images in the video-signal
without low-pass filtering the images or increasing their sizes. An
example of this would be making the sharp areas of an image look
duller without decreasing the "sharpness" setting [an example of low-
pass filtering] on the monitor or increasing the size of the image.
Normally, when the size of an image is decreased, its sharpness
increases [it's like compressing a lower-frequency sound wave into a
higher-frequency one]. Likewise, when the size of an image is
increased, it looks duller [like stretching a higher-frequency sound
wave into a lower-frequency one]. Low-pass filtering simply decreasing
the sharpness of an image while increasing its dull characteristics --
which is what I don't want.

That's a reasonable summary of what you don't want to do. What do you
think you might do instead?

The video-equivalent of changing the 'pitch' of audio recording
without changing the playback speed.

That's just arm-waving words. Describe the result, not as an analogy,
but as a specification. If it turns out that you can't think critically
after all, I have no time for you.

#1 Decreases the rate at which objects in the video move without
decreasing the video's playback speed or eliminating originally-
rapidly-moving objects [such as the rapidly flapping wings]

Something has to give. If the flapping of the wings is slowed, so is the
motion of everything else.

The motion of 'everything else' *is* slowed. However, the playback
speed remains constant.

Explain how everything can slow town without increasing the time to
complete a motion. Sounds have duration and pitch. motion has no analog
of pitch in that sense. Describe the result you want, not "something
like" the result.

Repetitive or cyclical motion (such as a ball bouncing, or a wagon
wheel rotating, or a bird-flapping its wings, or an exposed model of a
piston engine operating, or a flag waving in the wind) in the movie
are slowed without lengthening the clip.

Tell me again how the crankshaft can take run one fifth speed without
using more time to make a turn.

#2 Decreases makes a still image less sharp by stretching everything
within the image without increasing the size of the image or
eliminating sharp portions of the original image

Huh?

Sorry that should read "makes a still image less sharp by stretching
everything within the image without increasing the size of the image
or eliminating sharp portions of the original image"

Tell me again how everything in an image can be stretched to double size
without making the image twice as big.

My bad.

You betcha.

Anyways, this is an original pictu
http://www-dse.doc.ic.ac.uk/~nd/surp...ormalimage.jpg

OK

This is how the picture looks after low-pass filtering -- YUK!:

http://www-dse.doc.ic.ac.uk/~nd/surp...ort.lopass.jpg

Fine detail (and noise) is gone.

I don't want low-pass filtering. I simply want all frequencies to be
downshifted similar to decreasing the pitch of audio without slowing
the playback speed. The analogy is lower the frequencies of all
components in the image w/out increasing the size of the image or
doing any low-pass filtering.

http://www-dse.doc.ic.ac.uk/~nd/surp...ab/report.html

Justify why you think that images and sounds are subject to the same
transformations.

Both #1 and #2 are visual-equivalents of decreasing the pitch of a
recorded audio signal without decreasing the audio's playback speed.

Says who? You're reasoning from false analogy again.

How is it false?

Images have no visual equivalent of pitch. Pitch is temporal. Images are
spatial.

Here's the deal: From now on, I'll only answer your technical questions
if you make a good effort to state all the assumptions behind it. I'll
work with you to get the assumptions out into the open, but I won't
answer a question until the assumptions are clear. Most of your
questions are so far into fantasy that the assumptions, once made
explicit, will likely seem contradictory even to you, and the question
will go away. E.g.: Don't ask me to explain the meaning of life without
our first establishing that life has a meaning.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Radium wrote:
On Aug 19, 8:34 pm, "Bob Myers" wrote:

Sampled analog systems are certainly
not very common today (unless you count certain forms of
modulation as "sampling," and in fact there are some very close
parallels there), but the theory remains the same no matter which
form of encoding is used. In any event, you must sample the
original signal at a rate equal to at least twice its bandwidth (actually,
very slightly higher, to avoid a particular degenerate case which
could occur at EXACTLY 2X the bandwidth) in order to preserve
the information in the original and avoid "aliasing."

Is the CCD [Charge Coupled Device] a "sampled analog system"?

Yes.

Jerry
--
A good newspaper is one that prints only what you want others to know.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Aug 19, 8:54 pm, (Dave Platt) wrote:

The fact that it's an AC (inherently-varying) signal being recorded,
means that *something* has to move... if only some amount of
electrical charge. If the electrons don't move, the output can't vary
and all you have is a DC voltage.

By "moving parts" I mean mechanical parts. Not electrons.

And, in fact, this concept of moving electrical charges is the basis
for one type of analog signal storage and playback device which has no
moving (mechanical) parts... the CCD, or Charge Coupled Device. It
consists of a large number of charge storage devices (typically MOSFET
transistors with dielectrically-isolated gates) hooked up as a sort of
shift register or "bucket brigade". Each gate stores a charge which
is proportional to the input signal present at a given moment in time.
Several thousand times per second, a clock pulse causes each storage
cell to generate an output voltage proportional to the charge in its
storage gate, and then to "capture" onto its gate the signal being
presented by the previous gate in the chain.

In effect, the signal is propagated down the chain at a rate
proportional to the clock rate.

Is CCD a form of analog non-volatile RAM?

Why aren't these devices used more than they are? They're not very
efficient, and they're noisy. Every time the charge is copied from
one cell to the next, a bit of imprecision (noise) creeps in... so the
fidelity isn't great. And, because the device has to be able to hold
a very wide range of charges (since the charge is directly
proportional to the signal level) the storage gates have to be fairly
large.

I wonder how a PC would perform if it used CCDs in place of digital
storage devices. Lots of errors.

The net result is that an audio CCD is capable of storing a
decent-quality signal for only a few tens or hundreds of milliseconds,
from input to output.

What is the highest frequency an audio CCD can input and output? My
guess is 0.5x the clock rate.

Another sort of a purely analog signal-storage device, with no moving
parts other than the electrons which convey the signal, is a simple
length of transmission line (with perhaps some amplifiers mid-way).

Where is the "storage" in this device?

Put a signal in at one end, get the same signal back out the other end
some number of microseconds or milliseconds later.

Where is the signal being stored?

Dave Platt wrote:
In article . com,
Radium wrote:

I'm curious to why there are no purely-analog devices which can
record, store, and playback electric audio signals [AC currents at
least 20 Hz but no more than 20,000 Hz] without having moving parts.
Most of those voice recorders that use chips [i.e. solid-state] are
digital. Analog voice recorders, OTOH, use cassettes [an example of
"moving parts"].

The fact that it's an AC (inherently-varying) signal being recorded,
means that *something* has to move... if only some amount of
electrical charge. If the electrons don't move, the output can't vary
and all you have is a DC voltage.

And, in fact, this concept of moving electrical charges is the basis
for one type of analog signal storage and playback device which has no
moving (mechanical) parts... the CCD, or Charge Coupled Device. It
consists of a large number of charge storage devices (typically MOSFET
transistors with dielectrically-isolated gates) hooked up as a sort of
shift register or "bucket brigade". Each gate stores a charge which
is proportional to the input signal present at a given moment in time.
Several thousand times per second, a clock pulse causes each storage
cell to generate an output voltage proportional to the charge in its
storage gate, and then to "capture" onto its gate the signal being
presented by the previous gate in the chain.

In effect, the signal is propagated down the chain at a rate
proportional to the clock rate.

Why aren't these devices used more than they are? They're not very
efficient, and they're noisy. Every time the charge is copied from
one cell to the next, a bit of imprecision (noise) creeps in... so the
fidelity isn't great. And, because the device has to be able to hold
a very wide range of charges (since the charge is directly
proportional to the signal level) the storage gates have to be fairly
large.

The net result is that an audio CCD is capable of storing a
decent-quality signal for only a few tens or hundreds of milliseconds,
from input to output.

Another sort of a purely analog signal-storage device, with no moving
parts other than the electrons which convey the signal, is a simple
length of transmission line (with perhaps some amplifiers mid-way).
Put a signal in at one end, get the same signal back out the other end
some number of microseconds or milliseconds later.

Once again, they're not terribly efficient and are prone to be noisy.

For storage of large amounts of information, in a small space, with
high fidelity, using digital storage techniques is much more
efficient - largely because each storage cell must only store 2
different information states (0 and 1) rather than a large number of
possible levels.

Come on, Dave, a CCD is a digital device, subject to aliasing. The
charges represent the signal at a particular instant of its average over
a particular interval. (My CCD digital camera can take time exposures.)
A CCD's content may not be quantized in amount, but it is quantized in
time. In a camera, where the charges pertain to individual pixels, the
result is also quantized in space.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Come on, Dave, a CCD is a digital device, subject to aliasing. The
charges represent the signal at a particular instant of its average over
a particular interval. (My CCD digital camera can take time exposures.)
A CCD's content may not be quantized in amount, but it is quantized in
time. In a camera, where the charges pertain to individual pixels, the
result is also quantized in space.

"Digital" and "subject to aliasing" are two different things.

As I believe the term "digital" is usually meant, it implies a
two-state (on/off) storage representation. It's not just that the
signal amplitude is quantized, but that the quantization uses a
power-of-two representation and storage system of some sort.

In that sense, an audio CCD uses a digital clocking structure to move
the charge along, but uses a non-digital system for representing the
signal level (a linear number of electrons). Yes, it's quantized in
time, and the electron charges themselves are quantized... but I don't
think that either of these qualifies it as "digital".

"Analog" is a very fuzzy and imprecise term, and I think that a CCD
can reasonably be called an analog system.

Even audio cassette tape is quantized in both time and amplitude, at
the level of the individual magnetic domains in the oxide or metal
particles.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Aug 19, 10:08 pm, Jerry Avins wrote:

Radium wrote:

The video-equivalent of changing the 'pitch' of audio recording
without changing the playback speed.

That's just arm-waving words. Describe the result, not as an analogy,
but as a specification. If it turns out that you can't think critically
after all, I have no time for you.

The purpose of this visual "pitch-shifting" is like a way to record/
playback/transmit/receive/store supreme-quality video while using the
least bandwidth and storage space necessary when low-pass filtering is
not an option.

Using this video frequency-shifting, a high-quality video can be
stored in an extremely slow moving video-cassette with limited amount
of tape. Due to the video-tape's extremely slow speed the temporal and
spatial frequencies of the incoming video signals must be downshifted
in order to be encoded at such slow speeds. Due to the limited length
of film in the cassette, the movie must not be made longer than what
it originally is. Due to other inadequacies in the film, the spatial-
frequency must also be decreased, but the image size must not
increase.

The motion of 'everything else' *is* slowed. However, the playback
speed remains constant.

Explain how everything can slow town without increasing the time to
complete a motion. Sounds have duration and pitch. motion has no analog
of pitch in that sense. Describe the result you want, not "something
like" the result.

A 2 hour high-quality movie should be able to be stored in device with
limited high-frequency response and limited amount of storage space.
There should be absolutely no aliasing -- temporal or spatial - but at
the same time, the length of the movie should not be increased, sizes
of objects in images should not increase, image size should not
increase and no low-pass filtering should be used.

Repetitive or cyclical motion (such as a ball bouncing, or a wagon
wheel rotating, or a bird-flapping its wings, or an exposed model of a
piston engine operating, or a flag waving in the wind) in the movie
are slowed without lengthening the clip.

Tell me again how the crankshaft can take run one fifth speed without
using more time to make a turn.

I wish I knew. This 'pitch-shifting' is a lot more confusing than I
thought. Yet I still find it so interesting. Sorry.

Sorry that should read "makes a still image less sharp by stretching
everything within the image without increasing the size of the image
or eliminating sharp portions of the original image"

Tell me again how everything in an image can be stretched to double size
without making the image twice as big.

Nothing in the image has its size increased. They are simply smoothed
out.

This is similar to a graph of digital audio in Adobe Audition. You
decrease the pitch of the audio in the file by half [without changing
the tempo] and the waves in the graph will appear twice as long but
without increasing the horizontal length of the graph.

I don't want low-pass filtering. I simply want all frequencies to be
downshifted similar to decreasing the pitch of audio without slowing
the playback speed. The analogy is lower the frequencies of all
components in the image w/out increasing the size of the image or
doing any low-pass filtering.

http://www-dse.doc.ic.ac.uk/~nd/surp...ab/report.html

Justify why you think that images and sounds are subject to the same
transformations.

The less sample rate you have in digital audio, the lower the
frequency of the audio must be in order to prevent aliasing. There
isn't enough bandwidth to include the higher-pitches.

Similarly an imaging device with insufficient spatial bandwidth will
result in image distortion if excessively fine detail is put into the
camera.

Hence, if you want to get decent imagery in a low-bandwidth imaging
device, your best bet is to decrease the spatial frequency because
transferring it into the imaging device.

Just like if you have an 11.025-KHz-sample-rate digital audio device,
you need to make sure the pitch of the audio you are inputting into
the device does not exceed 5.5125 KHz.

How is it false?

Images have no visual equivalent of pitch. Pitch is temporal. Images are
spatial.

Spatial frequency is how fine or dull an image is. Pitch is determined
by audio frequency. I am using the spatial frequency as an analogy.

Dave Platt wrote:
Come on, Dave, a CCD is a digital device, subject to aliasing. The
charges represent the signal at a particular instant of its average over
a particular interval. (My CCD digital camera can take time exposures.)
A CCD's content may not be quantized in amount, but it is quantized in
time. In a camera, where the charges pertain to individual pixels, the
result is also quantized in space.

"Digital" and "subject to aliasing" are two different things.

As I believe the term "digital" is usually meant, it implies a
two-state (on/off) storage representation. It's not just that the
signal amplitude is quantized, but that the quantization uses a
power-of-two representation and storage system of some sort.

I can buy that, but it's not how I would have used the term. I call a
two-state representation "binary". A storage system that is clocked is
subject to most of the restrictions and permits most of the useful
techniques of digital signal processing. Early transversal filters used
op-amps, with the coefficients being set by the resistor values.

In that sense, an audio CCD uses a digital clocking structure to move
the charge along, but uses a non-digital system for representing the
signal level (a linear number of electrons). Yes, it's quantized in
time, and the electron charges themselves are quantized... but I don't
think that either of these qualifies it as "digital".

I agree to use your term for the sake of this discussion.

"Analog" is a very fuzzy and imprecise term, and I think that a CCD
can reasonably be called an analog system.

Yet I'd lay a bet that you call the pictures made by means of a CCD
image sensor "digital".

Even audio cassette tape is quantized in both time and amplitude, at
the level of the individual magnetic domains in the oxide or metal
particles.

Oh, sure. In that case, the crystal radio that I built in the 40s was
digital too. The electrons came down the antenna one at a time even if
closely spaced. We need to draw a line somewhere, and I don't like the
idea of calling a flashlight a digital photonic device.

There are in principle purely analog storage devices. A loop of analog
delay line with a repeater in it qualifies. A memory based on that
principle was used to store digital signals in an early computer, even
though the device itself is analog. It used an acoustic delay in a
column of mercury.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Sun, 19 Aug 2007 23:26:16 -0700, (Dave Platt)
wrote:

"Digital" and "subject to aliasing" are two different things.

As I believe the term "digital" is usually meant, it implies a
two-state (on/off) storage representation. It's not just that the
signal amplitude is quantized, but that the quantization uses a
power-of-two representation and storage system of some sort.

My reading of the possible systems goes like this.

analogue - a continuous representation of the original signal
sampled - a representation of the signal at discrete time points
quantized - a sampled signal, but with the possible levels constrained
to a limited set of values
digital - a quantized signal, with the individual levels represented
by numbers

Aliasing is going to happen as soon as you move beyond the first line
of that list.

d

--
Pearce Consulting
http://www.pearce.uk.com