Low pass filter modulation

Can anyone suggest the best way to implement "low-pass filter modulation" which removes high frequencies in square (or compound) waves at the specified rate per second?

In addition to hardware, is there a DSP software application that can perform this function?

Claus Jensen

Reply to
Claus Jensen
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I can understand each word here, but I have no idea of what are you trying to say. Would you care to explain what kind of processing do you need?

Tunable filter? Adaptive filter? Nonlinear filter?

What function? It depends :)

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Not totally sure what you mean. A lowpass with controllable cutoff? That would be called a tracking filter and is customary on ultrasound machines and radar. Tracking means that the cutoff is scooted so you reduce bandwidth for echoes originating farther away from the transducer/antenna, IOW trading off signal bandwidth versus SNR.

I'll have to leave that question to others but you haven't mentioned frequency ranges.

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Reply to
Joerg

Let's say I want to low pass modulate white noise with a 20Hz sine wave.

IOW the upper cut-off frequency, to some predetermined extent, would vary sinusoidally at 20Hz.

Claus Jensen

Reply to
Claus Jensen

IOW, a voltage-controlled low-pass filter:

20Hz ~ >-----. \\ .-------. White | | | noise >------| |-. |---------> Vout | |__\\_ | '-------'

-- Cheers, James Arthur

Reply to
dagmargoodboat

1) DSP IIR filter with coefficents moved in real time based on this sine wave 2) switched cap filter where the clock frequency is moved based on this sine wave 3) tracking filter using variable transconductance amplifiers with the sine wave altering the transconductance. 4) fixed LPF and some sort of mixer scheme where the baseband is mixed up then down with an offset. The only reason this would work is the source is noise, so the frequency offset shouldn't be an issue. There is a dual of this using DSP.
Reply to
miso

u

Hey if that's what he wants, this looks like the perfect place to use the Voltage coefficient of the ZU5 (YU7 whatever the 'crappy' ones are.) tantalum caps. Except I'm not sure how to make it work at DC for his low pass filter.

George H.

Reply to
George Herold

Boy, that would be dirt-simple wouldn't it?

-- Cheers, James Arthur

Reply to
dagmargoodboat

Guys, don't spill the beans and broadcast all of the unorthodox analog tricks :-)

It works but when there is substantial signal amplitude you'll have to live with distortion.

(Harold, I can't see your posts because of gmail but I can when someone answers)

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Reply to
Joerg

What, Joerg? You can't white-list with your news-reader? Sheeesh! ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

Haven't found out how (yet). I am using Thunderbird. It does have a white-listing method for email but when trying to use that for a news account the feature is grayed out :-(

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Regards, Joerg

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Reply to
Joerg

Real men don't try to use an E-mail client as a news-reader ;-)

If you're into a single program-that-does-all, Agent _does_ both E-mail _and_ news-reading. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

Yeah, but I am not going through the hassle just because of one provider with sub-par ethics. Interestingly, it seems that (very few) of your posts get chopped by my new news provider. Like the one with the topic "IE crap". Maybe their filter took offense with the wording :-)

Also, in foreign NGs it seems hardly anyone uses the gmail domain anymore because there are never gaps in threads like here on s.e.d.

Anyhow, why would people have to use gmail when there are so many better option including free ones?

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Regards, Joerg

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Reply to
Joerg

d)

u

o you

d

DC

Yeah... And if he's looking at noise he probably doesn't care about DC anyway.

George H.

Reply to
George Herold

you

DC

No worries Joerg, I've been thinking of signing up at 'eternal- september.org' they give free access to Usenet. And then I can have access to all the sages at SED.

George H.

PS. would someone please respond so Joerg can 'see it' Thanks Geo

Reply to
George Herold

I have 53 entries in my white-list (covering google, yahoo, gmail and hotmail) before the blanket kill of those groups.

I would frown on any news provider who filtered on offensive language or any other form of censorship.

Obama has already indicated a desire to "regulate" the Internet, otherwise known as "suppress" dissent :-(

My attitude is different than yours... most "free" stuff sucks ;-)

I switched to Giganews a few months ago when Agent's "APN" source became too ratty for yet one more time. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I think the term "low pass modulate" is extremely misleading, if not just plain self-contradictory.

You want to apply the signal to a low-pass filter with a modulated corner frequency (maybe).

I'm with 'miso' -- there are a lot of ways to do this, choose the one that's best. Think about what's important to you, and make sure you understand the issues -- some filter topologies will 'pump' the signal at the modulation frequency, some won't, some (if not all) may not pump some classes of signals but will pump others.

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Reply to
Tim Wescott

Gmail is a free e-mail service, nothing else. It has nothing to do with Google groups.

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The movie \'Deliverance\' isn\'t a documentary!
Reply to
Michael A. Terrell

Maybe so but it's the same company and it was spewing spam like crazy. Until I deep-sixed it, after that it became nice and quiet in all the groups I follow. I wrote to them, didn't even get a response and nothing was done about it, so ...

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Reply to
Joerg

Shooting off your nose to spite your face ?:-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

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