Renders real HDLC + NRZI + AFSK/MFSK audio with the actual modulator, adds white noise to a target SNR, feeds it to the actual demodulator, and asserts frames decode — all in memory, no audio devices touched. If your live config (300 baud AFSK) passes here but fails over AVD, the modem is fine and the fault is in the RDP/cable audio path, not the DSP.
Click “Run DSP self-test”.