Sampling: What Nyquist Didn't Say, and What to Do About It

Dnia 20-12-2010 o 08:34:44 Tim Wescott napisa=B3(= a):

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My first thought was that fonts look a little bit to thin and bright. I use AcrobatReader 9.4.1, preferences/rendering: LCD,all options checke= d.

I've not looked at the document(s). But, if you think carefully about how you build a PDF (e.g., which fonts you embed, what resolution you use for images, etc.) you can exert a great deal of control over the finished size of the document. (you also need to consider which PDF version you support -- it's annoying each time Adobe creates a new version of Reader/Acrobat and you are forced to upgrade just to view someone else's "new" document).

For example, when I include detailed photos, I deliberately chose high enough resolutions that allow the user (reader) to "zoom" to examine high levels of detail without the image being rendered with jaggies, etc.

Also, note that cropping an image in the PDF doesn't discard the "invisible" portion of the image. This can be embarassing if you think you've hidden (not included) a portion of the image that isn't "visible" :>

Finally, note that the PDF is tagged with several items from your "writing environment" (user name, etc.). Just be sure you know what's embedded "behind the scenes".

HTH

I agree, the font makes it very difficult to read, and is not conducive to enhancing reading over a long term, namely longer than one page..

Good idea, it looks good.

I have looked at the document - but not read it. I'll do that when I have time to do it justice.

Tim has used pdfLaTeX - the usual tool of choice for publishing technical or academic papers. So the CMR fonts are embedded as needed to make the document self-supporting. The images appear to be vector format rather than bitmap, so they scale nicely.

No sane person /chooses/ to use Acrobat Reader any more. It is annoying and insecure bloatware, and spreads itself over far too much of your system (hint to Adobe - it's been a decade since it was acceptable for a simple application to require a reboot of windows during installation). It is /far/ slower, and takes orders of magnitude more memory than common alternatives like Foxit on windows or Evince on Linux. And it has such a bad security record that I am considering banning it from our company. Unfortunately, there are occasions when someone has made a document that will only work with the latest Acrobat Reader - and I fully agree with you that it is annoying. But Tim's documents are pdf

That's a good plan, and something people often forget about - the result being documents that look good on-screen, but poor in printout. In this particular case, however, it seems the graphics are in a vector format (pdf files support eps), which is the best choice for drawings.

This is seldom an issue with pdf files (though it be, depending on the tools used to create it) - it is commonly found in MS Word files. But Tim has used pdfLaTeX - the pdf file contains exactly what he wants it to contain.

Again, pdfLaTeX adds the tags /you/ want it to add, and nothing else. But since Tim has his name on the front page, and every page's footer, I'm guessing he won't mind if the pdf file is also tagged with his user name!

The fonts are terrible. They seem to be bitmap fonts and not vector. It looks like you used TeX to generate the document. Go to

Regards Anton

On a sunny day (Mon, 20 Dec 2010 01:40:32 -0800) it happened Robert Baer wrote in :

I think the fonts look great, watching full screen on a 1680x1050 LCD with xpdf in Linux. wget

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Tank you, I found Foxit a fast an suitable pdf viewer. I like it. I also agree that Adobe Reader is extremely annoying and slow and uncompatible with his own previous versions. Now Tim's document look better.

No, they do look a bit "bitmapped" I'm afraid. I am also using xpdf in linux. A minor detail though, still quite readable IMO.

Dang, it's like people haven't seen Computer Modern before. Maybe you need to use Times New Roman, turn off kerning, and ditch the ligatures so that it "looks right." Maybe it's the em-dashes. Jeez...

I, for one, salute your leet Latex skilz. And thank you for taking the time to make these available.

Getting /almost/ on-topic again, the issue is, I think, that xpdf doesn't do anti-aliasing very well and so the fonts look a bit poor at low resolution. Evince does better. But in general, CMR fonts are better on high-resolution devices - they were designed for use on laser printers, not to look nice on screens.

What reader are you using? I'm getting a two-valued distribution here: "looks great!", and "looks nasty!". If it's a reader issue -- particularly if you're using Adobe -- then I'd like to test on the 'bad' reader.

What reader were you using? I'm trying to figure out (a) why some people think it looks peachy and some think it looks terrible (it looks great on Evince), and (b) make sure I test it on enough different readers that I get a true picture of what it looks like to the world at large.

it looks peachy and some think it looks terrible (it

readers that I get a true picture of what it looks like to

Tim,

I just looked at it using Adobe acroread under Fedora 13, with TeXLive 2010 installed (so that even if you hadn't embedded the fonts I should still have them available without substitution), and I agree with Anton - the fonts are bit-mapped and not vector. I use the TeX->ps->pdf route (using dvips and ps2pdf14) and, other than the -Pdownload35 option to dvips, do nothing special to embed my fonts and ensure they are vector.

Em 20/12/2010 05:34, Tim Wescott escreveu:

Tim,

I gave a diagonal look at the paper, as I got curious about the complaints on the font. They look OK to me :-) I'm used to read math's articles written in CMR fonts so perhaps I'm not a good judge on this.

However, my attention was caught on a link you quote in the footnote number 13 and I discovered it is not longer available at that address :-(

Maybe you can get the paper updated at some time!?

Regards,

It was there last week when I double-checked it! I'll see if I can chase it down.

I sold a couple hundred thousand channels of an AC power meter, used for utility end-use surveys, that sampled the power line voltage and current signals at 27 Hz. I had a hell of a time arguing with "Nyquist" theorists who claimed I should be sampling at twice the frequency of the highest line harmonic, like the 15th maybe.

John

If you've got something like an SCR spike that lands on a different spot in the cycle each time then subsampling isn't going to build up a true picture. But for truly repetitive signals, it's got a lot going for it (it's how really really fast sampling scopes work -- even today you can build a sampler that'll work a lot faster than an ADC, fill in the blanks).

I don't see anything at all wrong with the font. The one thing that I would change is the line length. It looks like a typical line is upwards of 110 characters. That's a bit too much to read comfortably. If you want to use a font that small, and don't want wide margins, I'd recommend going to a two-column format.

John,

If your AC signal had more than 13.5 Hz of bandwidth, how were you able to accurately sample them at 27 Hz? As far as I know, even subsampling assumes the _bandwidth_ is less than half the sample rate (for real sampling).