It takes a minute or so tо adjust the biasing modes. The idea behind the circuit is to always force a mid point bias for the modulator, so that when the circuit is used for something useful (like a Class D amp), the output waveform should stay without offset. The design still needs optimizing for full range audio, because most frequency sensitive components in the circuit were designed for quickest simulation. In reality to cover the full audio spectrum, a more precise frequency response is needed.
