Proper way to bandpass oscillators to prevent aliasing
I'm using the 1467 evaluation board and Im trying to output tones ranging from 20-20,000hz. Im using the generators and according the the wiki I need to bandpass these to prevent aliasing. Its very noticeable and Ive had some success using LP-filters but I think Im doing it wrong. Even with a sine-wave the reflections as I sweep the frequency higher are noticeable starting around 10k.
Any help would be appreciated.
The EVAL-ADAU1467 allows programming of the AD1937 codec over I2C by changing the switch from "standalone" to I2C and using MP24 and MP25 in secondary I2C mode. A sample rate of 48 kHz can theoretically generate a 20 kHz tone, but it only leaves 2.4 samples per cycle. Also, the antialiasing filter is never a complete brick wall allowing some foldback as you are seeing. I would strongly recommend using the SigmaDSP and CODEC at 96 kHz if you can handle the MIPS hit.
Ken
Many thanks. I thought changing the sample rate in Sigma Studio would also set the codec to that rate and the standalone switch was for self booting the unit.
A word of caution: Changing the sample rate at the top of the screen only changes the sample rate used for calculations by the compiler. You must also adjust the M/N ratio in the clock generator register page.
The Master Control Port IO block can be used to send the programming sequence to the CODEC. The simplest way to generate the XML file is to drag an AD1937x block into your Hardware Configuration tab, configure the CODEC registers, hit compile-link-download, copy the instructions from the output window to the sequence window, then save the sequence as an XML file.
Ken
Hi to all, this is my first post on this forum.
I've find this post becouse I heve the same difficulty.
My project is to feed this board with two signals, One at 48kHz band and One at 192kHz band.
In the Output I want each type of signal like input. I set the software at 192kHz and the correspondent output1 at fs 48kHz and output2 at 4xfs this last output don't feed audio.
I think that the codec isn't setted to work at other frequency more 48.
there is a procedure to control the parameter of AD1937 onboard?
thanks in advance
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