When I multiply my signal with a DC ( = 1 ) I don't get any response in probe. is that so ?
The easiest way to implement custom filters in SigmaStudio would be to generate your filter coefficients with your favorite filter design tool, and just enter the coefficients in the IIR filter block (one of the options in general filters). This still uses the same direct form II biquad structure. This cell works with the stimulus/probe blocks. In general, you won't be able to use the probe window when you're building custom filters with low-level blocks (multiply, delay, etc.)
What sort of custom filters are you trying to build that aren't part of the standard SigmaStudio library?
You are correct that the probe window will not show a signal multiplied by a dc source. The output of a multiplication block will not be shown in the probe because it is not "aware" of the actual signals, only the frequency response of the signal flow. If you implement this same flow with a volume control, which is essentially just a multiplier, the change in level will be properly displayed in the probe window. This is because the multiplier value is saved in the parameter RAM, rather than being a data value passed from one block (dc output) to the multiplier.
But how can I build and check an own digital filter using unit-delays and coefficiants ?
Is there another possibility to use coefficiants to multiply with the signal AND to check the result with stimulus/probe ?
I'd like to build a custom filter with low-level blocks , because I want to vary coefficiants with an external contol ( ADC Input )
Each biquad filter is controlled by five coefficients, so I'm not sure that you'd be able to directly control those from an ADC input. If you need external control of the filters without a microcontroller, it might be better for you to try the lookup filters blocks. This allows you to save an array of filters in the parameter memory and toggle between the different settings through some external control. There are example projects showing this included with the SigmaStudio installation, and I believe that there have also been some threads on this forum related to their use.
You may be able to get some ideas of how to use the Auxiliary ADC to change parameter values by reading this application note.
The section called AUXILIARY ADC SLEW MULTIPLEXER might help.
Thanks Brett, very good document and advices in there !
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