The Gentner DH20 is a specialized professional audio interface engineered to bridge broadcast studio consoles with standard telephone lines, enabling high-quality, on-air telephone conversations for radio talk shows, interviews, and listener call-in segments. It operates by interfacing directly with a telco line via an RJ11 connection and processing the two-way audio to manage levels, reduce noise, and prevent objectionable artifacts common in telephone audio, such as clipping, echo, and line noise. The unit serves as a critical link, extracting the caller's voice from the phone line and feeding it cleanly into the broadcast mixer while simultaneously injecting the host's audio from the console back onto the line for the caller to hear, all while maintaining proper impedance matching and isolation to prevent hum and ensure broadcast compliance. Its design is focused on delivering reliable, intelligible telephone audio that meets the stringent quality expectations of professional broadcasting, transforming the inherent limitations of a standard phone line into a usable broadcast source.

A core feature of the DH20 is its sophisticated hybrid circuit and digital signal processing, which work in tandem to achieve exceptional sidetone cancellation and echo suppression. This prevents the caller from hearing their own voice delayed (an effect known as talker echo) and stops the studio's program audio from feeding back into the broadcast mix, which are common pitfalls in telephone interfaces. The device typically includes comprehensive control over key audio parameters, such as adjustable input and output levels for both the line and studio sides, variable noise reduction or gating to minimize line hiss during caller pauses, and often a "cue" output that allows the producer to monitor the raw line audio before it is sent on-air. These controls enable the audio engineer to tailor the sound of each caller in real-time, compensating for varying line conditions and handsets to present a consistent, professional on-air product.

Physically, the DH20 is constructed as a rugged, half-rack or standalone desktop unit built for the demanding 24/7 environment of a broadcast studio. Its front panel provides immediate access to essential controls and status indicators, while rear-panel connections accommodate XLR or quarter-inch TRS connections for studio-level audio interfacing. The device represents a dedicated, single-purpose tool from an era when high-quality telephone interfaces were essential broadcast infrastructure, offering a level of audio processing and reliability that generic phone couplers or simple hybrid boxes could not match. It ensures that listener interactions, a vital part of many radio formats, are integrated into the broadcast seamlessly and with clarity, preserving the production value of the program.