Twenty-fourth octave filter and output level measurement - ADAU1761?

Gerry1 Question

Sep 21, 2010 00:00

Hi

I need to implement a 1/24 octave BW filter for use in stepped sine frequency response testing (20-20000 Hz) in a prototype test and measurement setup. The filter would be centered on each measurement frequency in turn and the signal amplitude measured (also 1/24 octave spacing of measurement frequencies).

I'm wondering if it might be possible to do this with the ADAU1761 - using the EVAL-ADAU1761Z board and SigmaStudio?

Is it possible to implement such a loop structure in SigmaStudio, where the digital filter would be stepped through center frequencies in turn?

Could the ADAU1761 eveluation board be used to carry out the level measurement of the filter output? An accuracy of +/-0.5 dB would be adequate.

Any advice would be appreciated.

thanks

Gerry

Audio Signal Processors

octave

filter

SigmaDSP Audio Processors

adau1761

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ADIApproved Reply

Sep 21, 2010 00:00

It is certainly possible to do this using the ADAU1761. You can make a large index table of filters and then step through the indices to select each filter for the measurement. However, it would be a bit complicated. Having a microcontroller do this for you would actually be much simpler. Will there be a microcontroller in your design? I assume there would have to be, in order for you to read back and store the measured level for each band.

This post should help explain how the signal monitoring would work:

Monitoring average and instantaneous signal levels

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Gerry1 Reply

Sep 21, 2010 00:00

Brett

Thanks very much for your help and for the very useful enclosure.

I wondered if I might be able to use the actual evaluation board and PC for my prototype measurement system. I would eventually like to use a microcontroller - provided I could do it with minimal or no assembler - I'm not a good assembler programmer and I know it would take me too long to put together

thanks again

Gerry

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ADIApproved Reply

Sep 22, 2010 00:00

If you are using the PC and eval board, then this will be easy! It won't really be that easy to automate, but changing the filters and making the measurements is relatively simple. For a very early prototype, you could do it manually.

At first you could do this with a simple white noise generator connected to the output and then the input connected to a single bandpass filter and RMS level detector, followed by a DSP readback cell. Most of that is already detailed in the forum topic from my previous link. You then simply need to manually update the filter center frequency and make the measurements.

All the time, the Capture Window in SigmaStudio is showing you exactly what needs to be read and written on the microcontroller side in order to duplicate the operations you're executing via the GUI. When you eventually do the implementation, all of the control writes will already be readily available in the capture window. So, it's all written out for you - you just need to implement it.

Most modern microcontrollers have a C compiler, so I don't really think Assembly will be necessary if you don't have experience with it.