J. Kissel

As I'm trying to make changes to other filters in the h1calcs model -- whose foton file is 
    /opt/rtcds/userapps/release/cal/h1/filterfiles/
        H1CALCS.txt 
-- I keep seeing foton's "File Errors" red box appear next to the filter file listed in the GUI interface -- see attached.

The error message is referring to the low pass filters in the I and Q banks of the new(ish) PCAL XY comparison, e.g. 
Warning: filter 1 module CS_TDEP_PCAL_X_COMPARE_ERR_DEMOD_I had at least one pole with a small
  frequency. Poles with frequency less than 10^(-6) as fraction of
  sample frequency will suffer from low precision.
  Consider running the filter at a lower sample frequency.

I'm never sure if foton counts from 0 or 1 in its messaging, so I'm not sure if "Filter 1 module" is FM1 or FM2. So, I list all three filters that are in these banks below:

FM1 "LP300s"
    Command: butter("LowPass",4,0.0033)
    Alternate:     zpk([],[0.003048802457154851+i*0.001262977001249471;0.003048802457154851-i*0.001262977001249471;
        0.00126285532697085+i*0.003048788768825331;0.00126285532697085-i*0.003048788768825331],
        0.9999794439618445,"n")

FM2 "LP30m"
    Command: butter("LowPass",4,0.000555)
    Alternate: zpk([],[0.000512753140477464+i*0.0002128241445590586;0.000512753140477464-i*0.0002128241445590586;
        0.0002123893051084369+i*0.0005125483540322335;0.0002123893051084369-i*0.0005125483540322335],
        1.000081799778788,"n")

FM3 "LP60s"
    Command: butter("LowPass",4,0.017)
    Alternate: zpk([],[0.01570595205275844+i*0.006505637221348701;0.01570595205275844-i*0.006505637221348701;
        0.006505618350371988+i*0.01570594367905692;0.006505618350371988-i*0.01570594367905692],
        1.000000060520675,"n")

My guess is that it's the 30 minute low pass in FM2 "LP30m" (so counting starts at 0 for this error messaging system), since that would be the low pass filter lowest frequency poles. This filter has poles at 0.55 mHz, which means they're 0.55e-3 Hz / 16384 Hz = 3.39e-8, which is definitely lower than 10^-6.

It looks like the team has chosen to use FM1 "300s", browsing through the DEMOD settings as they stand; see e.g. the attached screenshot of PCAL_Y_COMPARE_DEMOD overview.

So -- we should just delete these filters that foton complains about.

But, rather than just deleting it, I aLOG it 
    (a) for the team to understand what the issue is, 
    (b) for them to conscious for these warnings next time, and 
    (c) to document it for the CDS team, since I wonder what impact this has*** and if we can instead push this message to the user as soon as the design string is written such that the user knows that this is against the rules.

*** Impacts?
    - What happens if I switch to *using* such a filter that has this error? Does it round the frequency up and still low pass?
    - What happens if I save the file after making an entirely independent filter?