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Filter Implementation AD1941


I am trying to implement FIR and IIR filter in AD1941 DSP board. Can anyone please provide me any guideline from the beginning or help me with the code. 

Another question is AD1941 board is ok or should i change it and any suggestion for other suitable boards?



  •      Hello Shifat,

         To begin, download SigmaStudio and the Eval-AD1940 MINIBZ User Guide if you haven't already.  The User Guide takes you through the basics to get the eval board running and using SigmaStudio to make an audio EQ.  Where to go from there depends upon what sort of filters you need:

    The toolbox includes many stock IIR filters for which SigmaStudio calculates the IIR coefficients for you, such as the top two shown below.  There's also a FIR filter, however its AD1940 implementation doesn't build a kernel (list of coefficients) for you -- you need to calculate them elsewhere and type in or import them.  The example here is a 12-tap moving average lowpass filter:

    Use the Stimulus and Probe cells to predict the frequency response of stock filters and their combinations -- see this document for more info.  For example, the predicted response for these filters is shown below:


    Continued below  ...

  •     Do you need to calculate multiple sets of IIR coefficients?  SigmaStudio's Fixed Point Filter Table Generator (Tools menu) can help with this:

    You can calculate your own IIR coefficients using a spreadsheet like the one attached below.  For example, I calculated the coefficients for a 50 Hz, 6 dB boost filter from the spreadsheet, copied them into a General Second-Order Filter set for IIR Coefficient Entry, and got the response shown below.  You can extract the formulas from this spreadsheet and code them in C for use in a microcontroller if needed to calculate coefficients on-the-fly in your application product.

         Finally, if you wish to get into the theory of FIR and IIR filters, download this book which Analog Devices and its author has made available:  The Engineers and Scientists Guide to Digital Signal Processing  This book includes formulas for calculating FIR kernels as well as IIR coefficients.

         The ADAU1940 is among the older SIgmaDSPs, although still in production.  It can do quite a lot, yet others may be more suitable depending upon your application.  For example:

    The ADAU1701 has built-in converters and can self-boot, making it best for self-contained projects.  It's often considered the ideal chip to cut one's SigmaDSP teeth with.

    The ADAU1761 's low-power operation fits battery-operated devices.  It has built-in converters but no self-boot.

    The ADAU1452 is much more capable than the above & can self-boot, but you need to add external converters

    There's also extremely low-latency SigmaDSPs for noise-cancelling headphones, but these have limited functions.

         Hope this helps you get started with your ADAU1940 board, SgmaStudio and filters.

         Best regards,


  • Hello Bob,

    Thank you very much for your detail reply. It will help me a lot. Actually i want to see the frequency response, step response or magnitude response for different order of iir filter and Also for FIR filter i want to know how much can be the maximum filter length?