[sdiy] Shruthi 4PM (was re something else...)

Dave Manley dlmanley at sonic.net
Thu Nov 28 08:48:18 CET 2013

rburnett at richieburnett.co.uk wrote:
>If you take a look at Olivier's technical description here...
>...you can see that the cascaded 4-pole filter intrinsically produces 
>the four low-pass responses.  So these responses will be of good
>and not subject to resistor matching tolerances.
>It is the other responses (band-pass, high-pass and notch) that are 
>constructed from carefully chosen weighted sums of the input and the 
>four lowpass outputs.  So the purity of these "constructed responses" 
>depends on how accurate the weightings of the various signals are in
>final mix.  This is where tight tolerance on the mixing resistors will 
>reduce "non ideal" artifacts in the constructed responses, like LF 
>bleed-through in the stop-band of a high-pass filter.

This is exactly my point.  The non-LP modes are very sensitive to tolerance of the summing resistors.  I'd really like to see in bench testing how well the other modes match their calculated response.


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