 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
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