Ну вот и фсё: "All 1-bit converters produce high levels of ultrasonic noise and they tend to have troublesome low-level idle tones within the audio band. Each additional bit reduces the total noise output by 6 dB. In the late 1990*s, this prompted a move to 1.5, 2, and 3-bit oversampled conversion, and the 1-bit converters became obsolete.
Most modern oversampled multi-bit D/A converters use a number of equally weighted 1-bit converters running in parallel. One early example is Benchmark*s 1997 introduction of the DAC2004, a 20-bit D/A converter built with a 2-bit internal architecture. At that time, we used two one-bit Phillips TDA1547 "bit-stream" converters to create the 2-bit architecture. A short time later, IC manufacturers began introducing single-chip solutions".