Help designing a variable HPF/LPF with adjustable resonance?

Hello Filterproject,

There are so many posts with example project on the forum.

Sure DSP - Crossover function - Q&A - SigmaDSP Processors & SigmaStudio Dev. Tool - EngineerZone

Audio filtering for radio communications using ADAU1700/1 - Q&A - SigmaDSP Processors & SigmaStudio Dev. Tool - EngineerZone

You can take some idea from these posts and build your own.

If you want to know any info reg any modules, just drag and drop them, highlight the module and click F1, you will get the block's info from wiki page.

You can also search the forum with key words to get similar posts.

Regards,

Harish

It looks like the 1701 isn't suitable for my intentions. With a lookup table limit of 63 the sweep across the range of frequencies I'm looking to cover would be very choppy. Guess I just need to purchase or build a true analog solution. 

Hello Filterproject,

You are not 100% correct about the limit of 63. If you set the input format to fractional then 63 is the limit because it is looking for a 5.23 number but if you set it for Integer input then it takes a 28.0 number so the table could be huge!! You will run into memory issues eventually. 

Then, your comment about it being choppy does not take into account that we have a slew for the filter. When you change between two filters it will slew the filter coefficients from the old filter setting to the new one. This will help it not be choppy but also keeps the filter stable. 

The ADAU1701 is one of our early SigmaDSP but is still a great solution and cost effective. If you need higher performance then jump up to the ADAU1452 and an external codec. 

I am planning on making some videos about how to use lookup tables. It is high on my "ToDo" list for this spring!

Dave T

Hi Dave, 

Thanks for the reply. I guess I'm in well over my technical understanding level. The reason I am trying to work with the 1701 is because I just happen to have one on hand that I was previously using for a basic 2.1 audio project and hoped to re-purpose.

My inspiration is the filter on this and similar mixers - starting at 9:57 

youtu.be/RS0wm4n_C7M

In retrospect I'm not even sure that I need variable Q, especially if that's going to take valuable processing headroom needed for the frequency table. At the end of the day I am just looking for is a sweepable filter (or filters) with a 250Hz starting low cut point and a 2.5 KHz starting high cut point on an 18db/oct slope, but I need it to have a smooth, organic sweep like that mixer. If the 1701 is capable of pulling that off then I'm all ears. 

Hi Dave, 

Thanks for the reply. I guess I'm in well over my technical understanding level. The reason I am trying to work with the 1701 is because I just happen to have one on hand that I was previously using for a basic 2.1 audio project and hoped to re-purpose.

My inspiration is the filter on this and similar mixers - starting at 9:57 

youtu.be/RS0wm4n_C7M

In retrospect I'm not even sure that I need variable Q, especially if that's going to take valuable processing headroom needed for the frequency table. At the end of the day I am just looking for is a sweepable filter (or filters) with a 250Hz starting low cut point and a 2.5 KHz starting high cut point on an 18db/oct slope, but I need it to have a smooth, organic sweep like that mixer. If the 1701 is capable of pulling that off then I'm all ears.