It’s hard to imagine creating great radio without listener interaction, and the classic form of interaction is the telephone. The basic technology of an analog telephone line (plain old telephone service, or POTS) hasn’t changed much over the years, but the ability to send and receive high-quality audio through that phone line certainly has.

Digital technology has given the telephone hybrid outstanding audio specifications in send and receive audio isolation, as well as the ability to adapt for ever-changing telephone line conditions. Digital audio processing has also improved the sonic performance.

While newer technology for telephony exists, the POTS line is still in common use. We picked four popular single-line telephone hybrids to compare.