Sony STR-DA1000ES Technical Background page 6

Block diagram of the S-Master Pro amplifier.
Sony generates a 1-bit pulse stream to switch a pair of FET power output
transistors on and off. The resulting output has more than enough wattage to
drive a loudspeaker.
The output transistors act like an electronic on/off switch for the power
supply voltage. The Low Pass Filter (LPF) converts the amplified
pulses to a smooth, continuous analog waveform.
The S-Master 1-bit pulse stream has much in common with the Direct
Stream Digital signal that Sony developed for Super Audio CD. If you look
carefully at the pulses, you'll see that where the audio waveform is positive, the
pulses are mostly 1. Where the audio waveform is negative, the pulses are
mostly 0. In this way, a 1-bit pulse stream can represent the audio signal. As
with a DSD signal, a Low Pass Filter (LPF) is all you need to recover the original
audio signal.
In the diagram above, (A) represents the output power pulse stream.
This combines two components, the original audio signal (B) and a
noise component (C). The audio signal (B) looks smooth and
continuous because the frequencies are low. The noise component (C)
looks abrupt and spiky because the frequencies are high. The Low
Pass Filter (LPF) effectively separates out the audio signal, for
extremely accurate music reproduction.
ES Receivers V3.0 Page 6