Hello! Can I kindly ask if it is possible to use the audio analyzer for characterizing an ADC using coherent sampling? the gui does not have possibility to adjust the generated sine frequency with a high precision (example if I set to 101 Hz GUI might set sinewave generation to 105Hz, which might not result in a coherent sampling, not to mention that DAC clock and ADC clock might have phase shift that translates in a skirt around the fundamental even when using blackman harris windowin). Is there any way to clock the ADC using the I2S extension? or is coherent sampling not guaranteed.
A phase shift shouldn’t affect the spectrum (which doesn’t show phase anyway), but a frequency difference will as the peak will then have spectral leakage. Using a good and appropriate window function is essential if not synchronous, which depends on what you are trying to measure and how accurately.
I would imagine the I2S extension can do this - but could you perhaps explain which ADC and what parameters you want to characterize?
Hi Mark! Thanks for your response! The ADC is not available on the market but it is a high resolution one. No problem from THD point of view, but the fundamental tone has a skirt that starts from above the noise floor and even above harmonics and affects the amount of bins I need to take into account for signal power. It would be helpful to synchronize the ADC clock with the DAC clock. Then any phase drift can be tackled. Windowing is a solution but not a perfect one. I tried using the one of the I2S clocks, but it does not seem to work. My question is if anyone can tell me for sure that the clock that is used for the DAC is also the one provided over I2S. Or if there is any way to provide an external clock and use that one for the DAC. Thank you!
Hi @chris.t, yes, the front-panel I2S, DAC and ADC all share the same clocks. The front panel has master (MCK), bit (BCK) and and LRCKs, so you could use those to clock your ADC ensure the clocks are perfectly matched. The LR clock will match the sample rate, the bit clock is 64X that, and the master clock is fixed at 24.576 MHz.
