Spectrum Filter Components

All filters now using LM324 op-amp
Using the LM324 op amp causes the filters passband to not be completely flat, there is a slop, most extreme for the Presence Filter
Started sourcing the passive components - Resistors and capacitors
- Seems that the site I was using the build the active Butterworth filters https://tools.analog.com/en/filterwizard/ takes into account what the discrete value of passive components are
  - All of the capacitor values seem to be standard
- Using Metal Film Resistors that have tolerances of %1, as every percentage a passive component is off from its nominal value "It turns out that the total variation of the filter frequency then in percent is the sum of the tolerances of the components." however, that is for RC filters, could be different for more advanced filter types
  - https://www.quora.com/For-an-RC-filter-taking-analog-signals-audio-what-is-the-effect-of-choosing-a-5-tolerance-resistor-versus-a-1-tolerance-resistor
- Seems like it is standard for capacitors to have 20% tolerance... If the above is true that could be troubling
- Will source from Mouser as shipping is free, Digi-key has an additional shipping costs of $20 for anything under $100

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