Order of Hi Pass + Low Pass filters?

Jan 18, 2012 at 11:02pm

Order of Hi Pass + Low Pass filters?

Hello I have a Low pass filter + Hi pass filter in my patch, each controlled by a single pot (dial) in an attempt to mimic a typical EQ section on a mixing desk. Anyway my question is would the signal chain go:

Signal>HI pass> Lo Pass> Out (or Vice Versa)

>HI Pass
OR Signal > Out
>Lo Pass

Hope the question is clear enough, thanks!

Jan 18, 2012 at 11:11pm

Typically these are shelving filters with fixed frequencies, but however, if i understand your question,
The Lowpass-highpass or Highpass-Lowpass
really shouldn’t make an audible difference, does it? But i think you can easily search the web for cicuit plans of any mixer.
I don’t understand
“>HI Pass
OR Signal > Out
>Lo Pass”

Are you thinking about patching them serial/parallel?
in the typical mixer, they are serial.


Jan 18, 2012 at 11:32pm

Hi thanks or the reply, yeah wasn’t the best worded question sorry about that, my diagrams could do with a bit of work but yeh it was whether they are serial or paralell, thanks!

Jan 19, 2012 at 2:16am

Actually, since the typical bands of those filters don’t cross, it also doesn’t matter if they are serial or parallel :)

Jan 19, 2012 at 4:18am

they need to be in series otherwise they just wont work
the exception to this is band pass which are generally in parallel

Jan 19, 2012 at 4:44am

oops sorry youre right, serial

Jan 19, 2012 at 4:51am

sorry but wouldn’t they work if they are shelving filters and turning the knobs is adjusting the gain? Clearly, their efficiency would be decreased a lot, but they would do *some* attenuation of the corresponding frequencies, no? And with bandpass you mean the mid attenuation? why is that parallel?

Jan 19, 2012 at 11:04am

if a hp filter is in parallel with a low pass, then the frequencies you want filtered out by the high pass (low frequencies) will be passed by the low pass and vice-versa, so everything gets passed. It will have an effect on the sound, but not as generally intended as indicated by the names “high-” and “low-pass”. tHis also applies to notch filters– they should be done in series

The converse is true for band pass filters, and therefore they should be aligned in parallel

Jan 19, 2012 at 4:59pm

This is not answering your question exactly, but if you want to create an EQ you will probably have more luck with the cross~ object which is purpose built for frequency splitting while every day use high / low / band pass filters are not :)


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