After some work and helpful web resources, one of our Raspberry Pi’s is now generating I2S signals.
You can see, that this is a 44.1kHz playback, the LRCLK frequency is 44.17kHz, the bit clock frequency is 2.778MHz which is about 64x LRCLK (almost, the frequency counter on the oscilloscope is not extremely accurate).
Having a look at the signal curves, you can see that there is a lot of noise and ringing on the signals. However, this is no problem, the voltages are never in the forbidden area.
Another interesting question is: How much jitter do we see on both clock signals? Using the statistics functions on the oscilloscope (which are not the best method to measure jitter) we see a jitter on the clock signal of about 800 ps. On the lower frequency LRCLK, the jitter can’t be measured with my oscilloscope anymore. It is too low – which is a good sign for a high quality sound reproduction.
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