Digital-to-analog converter boxes became a necessity for owners of older televisions with analog tuners to receive over-the-air TV signals when full-power stations in the U.S. completed the transition to digital broadcasts in 2009. However, these converters are only designed to receive and decode OTA signals, and they will have no effect on cable TV reception.
A digital converter box acts as a liaison between the antenna and the TV, receiving the signals available at that location, which are broadcast as streams of digital data, and converting them into the analog audio and video portions of the signal to be processed and displayed by a TV with an analog tuner. In essence, it serves as an external tuner for older model TVs, as the channels to be viewed are selected through the converter instead of by changing the channel on the TV.
Standard Cable TV
One advantage to even the most basic cable TV service is that cable viewers were unaffected by the digital TV transition, regardless of the type of TV being viewed, though you can view only the channels the TV can physically tune to. Basic cable signals, including the channels broadcast digitally over the air, are still transmitted in an analog format through the copper wires in the coaxial cabling, giving even TVs with analog tuners the ability to display them without the aid of a converter.
Digital cable service and channels differ from basic cable in that the transmitted signals are encrypted, requiring more than just a digital tuner to display those channels. Connecting a set-top receiver box or DVR supplied by the cable provider is the most common way for subscribers to gain access to digital cable channels and the features that accompany the service, such as the on-screen guide, though a digital cable-ready TV can provide that access without the box.
The encryption used with digital cable service is specific to that cable provider, meaning that even if a digital converter box also worked with cable transmissions, it still wouldn't have the ability to bypass the encryption and convert the signals for viewing. One device that you can use instead of a set-top box, also supplied by the cable provider, is a CableCARD. The subscriber inserts the CableCARD into the card slot of a capable digital cable-ready TV to gain access to all channels in the subscriber's programming package.