6 | Section 2
2.2 Studio Audio Connections
Mix-Minus
e Hx 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. e European term M-1 (mix minus one) is per-
haps a clearer term. A mix-minus is also sometimes referred to as a ‘clean feed’. e 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 rst 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. e best
consoles allow selective feeds to the phone system. is is useful since sometimes you want only
one microphone feeding the phone, but sometimes you want to 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 eects, etc. Some even provide for separate ‘on-air’
and ‘o line’ (recording) telephone modes.
‘Making do’ with an older console
Consoles made before around 1990 rarely had good support for mix-minuses, and almost never
for more than one or two. With one of these oldsters, some clever improvisation is going to
be needed. Here we describe a possible scenario that can be used as a starting point for your
situation. We assume an older console with Program and Audition as the main busses. ere
is another bus of some kind that can be adapted for mix-minus application. We’ll call this the
‘Utility’ bus. All sources, including the hybrid, will be assigned to Program, so the audience can
hear them, as usual. We will also assign most of these sources to Utility as well, just never the
fader with the hybrid’s own audio.
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