Phone calls can create a unique bond with your listeners. It enables them to be part of the show with a level of interaction that is far more personal than reading a text or a tweet.
Traditional Analogue Line
This is the traditional way that phone lines are handled in studios. A single analogue landline is used in the studio and a piece of equipment called a Telephone Balance Unit (TBU) is used to interface between the phone line and your mixing desk.
TBU's also require your mixer to generate what is known as a 'cleanfeed' which means the audio that is sent to the phone line excludes the voice of the person on the phone (to avoid echos). Most broadcast mixers and all of the mixing consoles that we sell generate at least one cleanfeed for a single TBU but not all mixing desks can, so please check the specification of your mixer.
TBU's work with traditional phone lines but if you have a digital phone exchange or SIP system, we can provide converters (called Gateways) to make it work.
TBU Options
Sonifex CM-TBU
The Sonifex CM-TBU is a budget system that provides a simple TBU solution for all analogue direct exchange lines.The unit is powered directly from the phone line making it easy to install. You can connect and disconnect the phone calls using the 'Line Connect' button. You can adjust the Send and Return volumes knobs on the front of the unit.

Sonifex HY-03
The Sonifex HY03 is the modern version of Sonifex's classic TBU which is been in use in radio studios around the world for over two decades. The HY-03 offers a high quality audio interface as well as remote connections to allow it to be controlled directly from most mixing desks. It can also output signals to signage systems such as SmartSign to provide visual indications when the phones ring.
The HY-03 is available as a desktop unit or in a rackmount configuration.
Sonifex DHY-04
The Sonifex DHY-04 is often described as the best sounding TBU in the World and whilst we cannot substantiate that claim, it certainly is as good as any we have ever heard!The DHY-04 offers improved audio fidelity compared with a HY-03 and boasts advanced features such as digital (AES/EBU) input/output, four 'speed-dial' buttons on the front and a web interface to allow configuration, line hold changes and call dialling.
The DHY-04 is available in three models:
- Standard - Works with traditional phone landlines (POTS)
- GSM - Works on any GSM network, just add a SIM card!
- GSM HD - Works on 3G data networks for hi quality calls
AEQ TH03 Digital Hybrid
The TH03 Digital TBU is available as a single line or dual line unit. In single line format it acts like a standard digital TBU converting a standard phone line into either analogue or digital (AES/EBU) input/outputs. It also includes the standard hardware I/O needed for remote control and triggering studio signage.In dual line format, the TH03 can generate it's own 'cleanfeed' between the lines meaning you can simply 'conference' the lines together to allow the studio presenters and both calls all via a single audio interface between the TH03 and the mixing console.
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