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Downsampling by averaging

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Downsampling by averaging

Postby robios » Wed Nov 25, 2015 5:19 pm

Hi,

I have PicoScope 4224 and I'm looking for an option to perform a downsampling by averaging but can't find it.

What I want to do is to capture a few millisecond waveforms without having aliasing. To avoid aliasing I set a sampling rate to 40Msps or more, but it unnecessary increases a number of samples. So I manually decimate (by averaging) the captured waveforms, but it's just a waste of time. Can PicoScope 6 do it for me?

BTW, the resolution enhancement applies a moving-average filter to captured waveforms, but it should decimate (by averaging like CIC filter) instead. The higher frequency band above fnyq/N, where N is N in https://www.picotech.com/library/oscill ... nhancement, is just useless since it is already eliminated by the moving-average filter.

Regards,
Kazuhiro
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Re: Downsampling by averaging

Postby Hitesh » Mon Nov 30, 2015 3:28 pm

Hi Kazuhiro,

The PicoScope 6 software has a Math Channel feature which will continuously average the waveforms collected since the start of the data capture.

This will limit the number of samples collected per waveform to 2MS (PicoScope 6.10.18 stable or earlier) or 5MS in the PicoScope 6.11.7 Beta version.

Please note that if the data is saved to file and later reloaded, the average displayed will only be of the waveforms in the data file.

If you are using the API functions in order to collect data using the Software Development Kit, then you can retrieve averaged data using downsampling.

I will feedback your comments about the moving average filter to our Development Team.

Regards,
Hitesh

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Re: Downsampling by averaging

Postby robios » Wed Dec 02, 2015 6:24 am

Hi Hitesh,

The averaging I meant is in other words rebinning. Say we have 10 samples (not 10 waveforms) t[0] to t[9] and want to down-sample by 2, we want to get 5 samples (t[0]+t[1])/2, (t[2]+t[3])/2, ..., (t[8]+t[9])/2.

Kind regards,
Kazuhiro
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Re: Downsampling by averaging

Postby Hitesh » Wed Dec 02, 2015 9:32 am

Hi Kazuhiro,

For downsampling with averaging, you would need to use the Software Development Kit.

We do provide support for a range of programming languages including C/C++, C#, (MS Excel) VBA, LabVIEW, MATLAB and VB .NET.

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Hitesh

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Re: Downsampling by averaging

Postby robios » Wed Dec 02, 2015 4:07 pm

Hi Hitesh,

I see. No official python support yet?

Kind regards,
Kazuhiro
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Re: Downsampling by averaging

Postby Hitesh » Thu Dec 03, 2015 9:11 am

Hi Kazuhiro,

Not at the present moment - please e-mail support@picotech.com in order to discuss this further.

Thanks,
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Re: Downsampling by averaging

Postby hexamer » Sat Dec 05, 2015 4:10 pm

robios wrote:Hi,

I have PicoScope 4224 and I'm looking for an option to perform a downsampling by averaging but can't find it.

What I want to do is to capture a few millisecond waveforms without having aliasing. To avoid aliasing I set a sampling rate to 40Msps or more, but it unnecessary increases a number of samples. So I manually decimate (by averaging) the captured waveforms, but it's just a waste of time. Can PicoScope 6 do it for me?

BTW, the resolution enhancement applies a moving-average filter to captured waveforms, but it should decimate (by averaging like CIC filter) instead. The higher frequency band above fnyq/N, where N is N in https://www.picotech.com/library/oscill ... nhancement, is just useless since it is already eliminated by the moving-average filter.

Regards,
Kazuhiro


I would strongly second the recommendation for a CIC decimator on the scope. In developing my application I was considering implementing a CIC decimator to solve a specific problem, but ended up solving it a simpler way - all the while wishing the scope already had true decimation. A modern PC is plenty powerful to perform decimation with a CIC+FIR compensator. But a significant benefit of doing this on the scope would be reduction in size of the transferred data. I don't know if it's realistic to do this with the current scope's FPGA (via upgrade), but maybe it could be considered on future scopes.
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Re: Downsampling by averaging

Postby Hitesh » Mon Dec 07, 2015 3:11 pm

Hi hexamer,

I have forwarded your comments to the Development Team for consideration.

Thanks,
Hitesh

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