problems with index selectable filter

Hello Stephan,

I see that you configured the DC cell to 28.0. This is the correct number format to control the Index Selectable Filter so I would normally expect the filters to change index.

Also, it's usually a good idea to use a DC Blocking filter right after the input block. Otherwise the small DC offset introduced by the converters can pass through the entire schematic.

Can you zip up your project and attach it here?

Joshua

Hi Joshua,

thanks for your answering so quickly, I'm impressed :-))

(typing "return" always sends the message, sorry, seems to be a browser issue). I did not find a way to upload the ZIP file, so you can download it from https://seafile.rlp.net/f/e1a9dce8bdf648d39b86/?dl=1. In the original more complex design I put a 50 Hz high pass filter right after merging the input signals. So I think the DC blocking is obsolete.

Hi Stephan,

I looked into this and there is a problem in the Index Selectable Filter for ADAU1701. I cannot select any filter except the one at Index 0, and the Index Selectable is overwriting parameters for some other blocks.

Until this is fixed, I think you should avoid the Index Selectable Filter for ADAU1701.

As a workaround you can use the standard Second Order Filter blocks followed by an index selectable multiplexer; I tested this and it works nicely. You can grow the multiplexer to match the number of filters you have.

PS, for others reading this - the Index Selectable Filter is working on ADAU176x, ADAU145x, and ADAU146x.

Joshua

Hello, looks like you posted this while I was typing my reply above! A 50Hz HPF will certainly be just as effective at the DC blocking filter. In case you would like to lower the cutoff frequency later, here is where the DC blocking filter is in the library. Its cutoff frequency is 0.1Hz when your system is running at 48kHz sample rate.

Joshua

Hi Joshua, thanks a lot for your support. This solution works like a charm :-) And thanks to all moderators in this forum! For nearly every problem I was running in I found a well explained solution. Great!