Sampling rate on Android phones

Question

I am trying to compare two recorded signals at the same frequency with different sampling rates. the first signal is sent and recorded at 44.1 khz (first spectrogram), and the second sent and recorded at 48KHz (second spectrogram). As you can see, it is clearer with less distortion at 48KHz. i m not sure what these red parallel signals are. is that aliasing effect? echoes? even though at 44.1KHz the signal verifies Nyquist-Shannon theorem (20KHz frequency of the signal).

I should also mention that they are sent from An android tablet and recorded by Nexus 4 phone.

Any explanation plz?

Answer 1

I believe the Nexus 4 phone uses 48kHz native sampling rate. In other words, for the first spectrogram the audio is really sampled at 48kHz, and then resampled and saved at 44.1kHz. What you are seeing on the first spectrogram is likely sampling rate conversion artefacts (from the resampling).

The second recording does not have to be resampled, and correspondingly the second spectrogram does not show such artefacts.