|Then you see a schematic like following. This has one AM modulator and
two demodulator. Lower portion of the schematic is the demodulator by a multiplier.
Do left click to select WAVIN (U_30) and right click to choose "Open a Monitor".
This is a 3kHz sine wave. Its frequency is the same as Carrier in modulator (U_1).
There is a DELAY (U_36) after WAVIN. Let's open a monitor.
This executes four samples delay. Since it's 3kHz and the sampling frequency is 48kHz, the phase will be shifted by 4 / (48k/3k) * 360 = 90 [degree]. This is to cancel the difference between two carriers