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pruning channels


Meredith Pecukonis
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Hi - I'm hoping to use the prune channels function in Homer3 but I'm not sure the best values to use.

I want to exclude channels if the magnitude of the signal is greater than 98% or less than 2% of the total range for longer than 5 s during the recording. Any tips on what values to enter for the prune channel function?

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Meryem Yücel
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These numbers may change from system to system. (For the techen system ideal values would be 10^4 to 10^7 for instance). Similar SNR threshold can be used across systems, a value of 5 should get rid of most of the noisy channels.

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Verena Schäfer
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Hello,

I would like to use prune channels and in the videos it is said that you only use dRange if you have the appropriate system such as Techen and if not then you should set it to 0 and work with the SNR threshold. When I do that, I get an error message (error at line 95: Index exceeds matrix dimensions) and it doesn't work. Can someone help me there? Kind regards

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admin
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@verena sorry for missing this earlier... it went into the moderator pile. Can you share the full error message?

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Verena Schäfer
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@admin

Hello the error message is: "Index exceeds matrix dimensions" Error at line 95.

kind regards🙂 

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David Boas
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There is usually more to the error message than "Index exceeds matrix dimensions" Error at line 95.

It should report the file name and/or function name. Odds are that this is an error that is arising in the hmrR_PruneChannels function. I looked at line 95 in that function which is

 lst2 = find(dmean(lst)>dRange(1) & dmean(lst)<dRange(2) & (dmean(lst)./dstd(lst))>SNRthresh & rhoSD>=SDrange(1) & rhoSD<=SDrange(2));

I suspect you are getting the error because dRange and/or SDrange don't have two elements each. These are the user supplied parameters for the intensity range in the data which must have two values, a min and a max, and for the source detector distance range, again must have a min and a max.

Can you show us the parameters you used for this function? I suspect you didn't provide the min and max.

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Verena Schäfer
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@dboas

we do not know what would be suitable values for dRange for our system (Hitachi ETG 4000) so we have set this to 0 and SNRthresh to 5 and SDrange from 0 to 45.

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David Boas
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@verena dRange needs to have 2 values separated by a space. So give it 0 and a very large number. Try 0 9999999

 

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Verena Schäfer
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@dboas

oh thank you very much!! It works now 😀 

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David Boas
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I'll note that we have on our to do list to check to see if the user has not provided proper inputs for the functions and to warn them of that in a user friendly way.

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