Potentiometer controlled Hi Shelving Filter

OK, I got a basic version working using one of the index select-able filters, but I can only adjust the gain. (I forgot to add a DC multiply to the ADC before)

Are there any filters with two control lines?

I tried adding multiple filters and a mux but ran out of system resources

Rich

Hi Rich,

What kind of application is this going to be for? There are no filters with controls for both frequency and level, but there are a couple ways you could "fake" it, depending on what the final use is going to be.

Regards,

Tyler

thanks for the reply. Its an audio project but must have a variable HF shelving boost. (long story....)

I have something working but its not ideal. I'm using a 2nd order lookup/slew control set to tone which works fine for the gain, then having multiple banks of these set to different frequency, and a multiplexer to select which to use controlled by the 2nd pot to select the frequency. it works, but I only have enough mips for three banks which is not ideal.

any other options?

Rich

Hi Rich,

Unfortunately, that's about the best solution possible for the 1701. The issue is that, when creating a filter in SigmaStudio, the filter coefficients are calculated on the PC side, then programmed to the chip. This relieves the chip of having to compute the filter itself, but it means that there isn't a good way to change filter parameters on the fly.

However, on newer chips (e.g. ADAU1452), the chip is capable of calculating filter coefficients on its own. If you're able to change out your 1701 for a 1452, I can come up with an example of how you could go about making an adjustable filter.

Regards,

Tyler

Hello Rich,

I tried making an adjustable shelf using the State-Variable Filter but it didn't work very well. Nonetheless, you may find the project shown below helpful. It plots frequency response of this and other circuits not amenable to the Stimulus-Probe tool (see Stimulus-Probe Capability and Limitations ):

Best regards,

Bob

Hi Bob

Thanks for attempting it anyway! The project is useful for me thanks for that too.

For now I am stuck with the 1701 so will have to accept its limitations

Rich