Hello Ed,
For the I2S part, you can check the following examples: sai_interrupt_record_playback and sai_edma_record_playback. You will need the playback part of this example for your own project.
Regarding the SD card, unfortunately, the SDK doesn't have any example that reads an audio file. However, there's an example that reads a JPEG file out of the SD card, you can use this example as a starting point for your project.
Hope it helps!
Victor.
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