Telos NX12 user manual Studio Audio Connections, Mix-Minus

Installation  11

The other thing to investigate is whether the PBX offers ‘Loop Current Wink’ or ‘CPC’ (Call- ing Party Control) on the analog ports. Without this supervision, the Nx12 will not detect that a caller on hold has hung up, and your talent will get a recording “please hang up and dial again…” or dial tone when attempting to air such calls.

2.7 Studio Audio Connections

Mix-Minus

The Nx12 must be fed send-to-caller audio that is free of the caller audio, a mix-minus. A mix-minus is a mix of all of your audio sources that will be placed on-air (or recorded) except the caller audio – thus the mix-minus designation. The European term M-1 (mix minus one) is perhaps a clearer name. A mix-minus is also sometimes referred to as a clean feed. The important thing to remember is that the hybrid must not “chase its tail” – the condition when its output makes its way somehow back to the input.

Hot Tip

Many hybrid installation problems are caused by an inadvertent signal path which creates a loop from the hybrid’s output back to its own input. Some consoles allow this when certain control combinations are selected by the user. In some cases, it may be as simple a mistake as assigning the hybrid to whichever bus is feeding the hybrid. This is the first place to look when strange or erratic performance is experienced. The quickest test is to bring up only the hybrid in question on the board and select a line. Dial tone should not appear on the send meter of the hybrid in question.

Using a modern broadcast console’s mix-minus capability

Most modern broadcast consoles have provision for multiple mix-minus busses. The best allow selective feeds to the phone system. This is useful since sometimes you want only one micro- phone feeding the phone, but sometimes you want three or four mics (during the morning show, for instance), and sometimes you want to play some audio piece that callers need to hear and react to such as contest sound effects, etc. Some even provide for separate ‘on-air’ and ‘off line’ (recording) telephone modes.

When multiple hybrids are used, each caller will need a separate mix-minus that includes the other hybrids so that callers can hear one another.

Hot Tip

The Axia Element mixing console was designed with today’s extensive use of phones and remote codecs in mind. It has all the features described above. It can have as many mix- minuses as faders. It offers an integrated phone controller module that works smoothly with the Nx12 over Ethernet. It has a one-button Record function that does everything needed to record an announcer + phone call off-line. Because it uses Livewire networking, only one RJ-45 is needed to connect the Nx12’s four hybrids input and output, two program-on-hold inputs, and all needed control.