Logarithmic charts in Numbers?

Question

Level 1

39 points

Logarithmic charts in Numbers?

Hi,
I'm sitting here with a report in my Electronics class where I'm supposed to visualize my filter measurements in a table and an attached chart. This is fine, no probs. I've done the math in Numbers and I've got my chart just fine.

However, I'm supposed to represent the frequency (x-axis) in logarithmic scale so instead of 20 40 80 160 320 640 1280 and so on up to 20 000 it'll read 20 200 20000.

Is this possible?

MacBook 2GHz, Mac OS X (10.4.9)

Posted on Oct 1, 2007 12:33 PM

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Answer 1

jaxjason

Level 5

5,063 points

Oct 1, 2007 7:56 PM in response to JonesH

It depends on the kind of chart which axis is allowed to be shown logarithmic. Basically, the axis that is "parallel" with the bars is allowed to be Logged. Scatters don't allowit it seems.

This si one place that I personally would like to see some improvement. I think the charts look great, but I really would like some more choices about how the charts look. Data point size and such that I cannot seem to change to my liking.

Please be sure to submit Feedback using the Feedback option under the Numbers menu.

jason

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Answer 2

5-vv

Level 3

685 points

Oct 1, 2007 8:25 PM in response to JonesH

This has no bearing on your question about Numbers, but just so you're clear: 20, 40, 80, 160, 320, 640, 1280, ... is a logarithmic sequence, log2(n/10), just as 20, 200, 2000, ... is logarithmic, log10(n/2).

And now for your question...

Are you trying to graph normal (non-logged) data in a table using chart with a log (non-linear) scale or does your table need to display logged data, which you then plot on a linearly scaled chart?

Jason's answer pertains to the former situation. If it is the latter, you should be able to introduce columns in you data table containing formulas for transforming into the log space. Then you can chart those using a standard linearly scaled chart (with units appropriately labeled as being 'log(data)' for clarity)

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Answer 3

JonesH Author

Level 1

39 points

Oct 2, 2007 12:23 AM in response to jaxjason

Hi,
Thanks a lot for your efforts.

My chart consists of frequency data on the x-axis (wich I want to display in log10, thank you 5|=vv) ranging from 20Hz to 20 000Hz, and level data on the y-axis (wich consists of corresponding data for each frequency, and is a formula that looks like this: =LOG10(Vin/Vout)*20.)

This is supposed to be represented in a chart (I think it should either be a scatter chart with the dots connected or a line chart), but I'm unsure how to do this and get it correct. If you could guide me I'd be really grateful!

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Answer 4

jaxjason

Level 5

5,063 points

Oct 2, 2007 9:06 AM in response to JonesH

send me some sample data your actually using, that would be easier to work with than making up something that might not match what your doing.

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Answer 5

JonesH Author

Level 1

39 points

Oct 2, 2007 9:18 AM in response to jaxjason

Thank you. As I've said, I'm matching frequencies against gain. This is the frequencies that sets the bounds for the x axis:

20
25
31
40
50
60
80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
12500
16000
20000

and these are my measurements in dB, corresponding to every frequency:

-16,250
-14,379
-12,468
-10,545
-8,826
-7,151
-5,564
-4,265
-3,160
-2,169
-1,514
-1,032
-0,696
-0,455
-0,309
-0,211
-0,140
-0,096
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044
-0,044

The x axis, frequency axis, ought to be logarithmic in 10's, it should read 20 200 2000 20000.

Thank you so much,

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Answer 6

jaxjason

Level 5

5,063 points

Oct 2, 2007 9:19 AM in response to JonesH

Click my name in this post. I opened my email address so you can send me an email with the file.

I cannot get to it till tonight when I get home, But I promise to look at it.

Jason

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