Max FIR size for ADAU1761

Hello Yair,

The two filters fit easily, as shown here. In theory there's enough chip resources to go much larger, although the compiler hiccuped when I tried it.

For all FIR filters in SigmaStudio, you need to come up with your own kernel coefficients, save them as a text file and import them into the FIR table provided (or type them in yourself, which of course is practical only for small filters). Thus you'll need to use an external program or spreadsheet to figure the coefficients for whatever FIR filter you desire.

Best regards,

Bob

Hi Bob,

Thanks for your answer. One last question:

I assume that there is a way (via SPI/2C) to download the required coefficients at run time using another processor? Specifically I'm looking at the EVAL-BF706-EZKIT board, that has this device and the BF706 on it.

Am I right?

Regards,

Yair

Hi,

On the ADAU1761 end, the answer is yes -- loading its code from another processor is frequently done. The exact implementation depends upon the other processor and its programming language, which is why documentation on this subject is unfortunately rather vague. I'm not familiar with Blackfin, so perhaps another member might be willing to help with that end of things.

Come to think of it, it's not practical to update a FIR filter at runtime due to the number of coefficients needed to change. SigmaDSP incorporates a Safeload feature to update up to five parameters at runtime without pops or clicks -- but this is designed for IIR filters.

Hello,

I'm coming back to my post after a long time, as I'm considering this device to a high volume consumer device.

The picture shown above shows that indeed the fitters can fit (but there is note saying that parameter RAM used is 1038 out of 1024). Is that a problem?

Also, this is a 50 MIPS device. Can it handle 2 x 512 tap FIR at 48KHz sample rate?

Hi Yair:

My suggestion is for you to use the ADAU1940, ADAU144x or ADAU145x. All these run above 75 MHz and have enough coefficient memory. Unfortunately neither one of them have audio converters built in. Alternatively slightly shrinking your coefficients for them to fit both in MIPS and memory will also work. On Bob's response I'm not sure why the assembler is yielding 80% utilization (we'll look into that). For FIRs on the 1761, it takes one instruction per coefficient (tab). This is very close to 100% utilization.

FYI, the ADAU145x can perform 4 tabs per cycle and therefore with it's 300 MHz performance, you can do a lot more FIRs if you need.

Miguel