A Bitstream or 1-bit DAC is a consumer electronics

Consumer electronics

Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...

 marketing term describing an oversampling

Oversampling

In signal processing, oversampling is the process of sampling a signal with a sampling frequency significantly higher than twice the bandwidth or highest frequency of the signal being sampled...

 digital-to-analog converter

Digital-to-analog converter

In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...

 (DAC) with an actual 1-bit DAC (that is, a simple "on/off" switch) in a delta-sigma

Delta-sigma modulation

Delta-sigma modulation is a method for encoding high-resolution or analog signals into lower-resolution digital signals. The conversion is done using error feedback, where the difference between the two signals is measured and used to improve the conversion...

 loop operating at multiples of the sampling frequency. The combination is equivalent to a DAC with a larger number of bits (usually 16-20).
The advantages of this type of converter are high linearity combined with low cost, owed to the fact that most of the processing takes place in the digital domain and requirements for the analog anti-aliasing

Anti-aliasing

In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...

filter after the output can be relaxed. For these reasons, this design is very popular in digital consumer electronics (CD/DVD players, set-top boxes and the like).