Using ADAU1772 for microphone beamforming

We used an ADAU1772 to create a simple microphone beamforming application, with two omnidirectional ADMP504 MEMS microphones mounted in an endfire configuration. While the ADAU1772 has no delay cells in its library, you can still create delay by using IIR filters and manually setting the coefficients to create delay paths. Setting coefficient B2 to 1 (and all other coefficients set to 0) creates a delay path of 2 samples, whereas setting coefficient B1 to 1 (and all other coefficients set to 0) creates a delay path of 1 sample. Using the attached Excel sheet to perform the calculations, we calculated that a total of 12 IIR filters are required to generate a delay appropriate for a microphone spacing of 42 mm. Distance between microphones (mm) 42 Speed of sound (mm per sample @ 48 kHz) 7 Speed of sound (mm per sample @ 192 kHz) 1.75 Samples to cover microphone distance @ 192 kHz 24 IIR Filters with B2 = 1 required to produce delay 12 The following project was created to realize the signal flow. The first 11 filters have IIR coefficients set with B2=1 and all other coefficients set to 0. The very last filter serves as a delay and an inverter, with B2 set to -1 instead of 1. Reference materials: Microphone Beamforming Application Note ADMP504 MEMS Microphone Datasheet ADAU1772 Datasheet Attachments: ez.analog.com/.../1817.ADAU1772_5F00_Beamforming_5F00_Test.dspproj.zip ez.analog.com/.../2514.EndfireCardiodBeamformingCalc_5F00_ADAU1772.xls

How to create an EEPROM image for the ADAU1772 that has different filter coefficients in Bank A and Bank B

The ADAU1772 has two separate filter coefficient banks. Here are the steps to create an EEPROM image that has different values in each bank using SigmaStudio. For this example, I will create a simple schematic with a single biquad that puts coefficients for a LPF in bank A and coefficients for a HPF in bank B. - In SigmaStudio, drag a USBI, ADAU1772, and E2PROM cell into the Hardware Configuration tab. Connect them as shown. - Create your schematic in SigmaStudio. Here I am using the stereo analog input on the EVAL-ADAU1772Z and routing the audio to the DACs. Create a LPF (or any type of filter for that matter). - Navigate to the Hardware Configuration tab and then to the Bank Select section of the Read/Write tab. Choose ‘Bank Switch via Register Control’. Then select ‘Bank A’. - Go to the Capture Window on the bottom of the screen (If you can’t see the capture window go to view/capture window). Then click the ‘Display Sequence Window’ button on the top right to open up the sequence window. - Click the red ‘X’ in the top left corner of the window to clear all output data. Now, click the Link/Compile/Download button. You will see the download sequence appear in the Capture window on the bottom of the screen. Highlight all of the writes and drag them into the sequencer window. Once completed it will look like this. - Now, go back to the schematic and change the value of the filter to a HPF. - Navigate to the Hardware Configuration tab, Read/Write tab, and Bank Select section again. Select Bank B. - Click the Link/Compile/Download button. In the capture window, you will see a write under the parameter name Bank B Parameters toward the bottom of the list. - Highlight this write. In the sequence window, locate the write for Bank A Parameters. Drag the Bank B Parameter write in the Capture window to the sequence window and place it directly below the Bank A Parameter write. - Save your sequence as an XML file by clicking on the ‘save’ button in the sequence window. - In the Hardware Configuration Tab, right click on the ADAU1772 cell and select “Create E2PROM image from sequence file”. This will write the sequence file to the EEPROM. Enable Selfboot and each power cycle will load up the schematic with the different coefficients in Bank A and Bank B. This FAQ was generated from the following discussion: How to create an EEPROM image for the ADAU1772 that has different filter coefficients in Bank A and Bank B