(English) 2019 eBook

Tech TIP: Setting up
IFB MIX MINUS
Sports Remotes
What is a Mix-Minus?
A mix-minus is a broadcast term used to
describe the feed sent from the studio
to a remote site, so that the remote site
can hear the output of the studio, without
the remote site hearing itself back. The
feed from the studio will often include a
full mix of the studio master mix output
(master mix bus), minus incoming audio
from the remote outside broadcast.
Why is a Mix-Minus Required?
Typically, a mix-minus has been used by electronic news gathering crews, radio and
television news reporters and remote outside broadcast trucks to facilitate live audio
crosses that require bidirectional communications. Sending a mix-minus feed from
the studio allows the remote site to hear studio broadcast audio without hearing the
audio from the remote site back on delay. Audio sent via satellite or IP technologies
from a remote site invariably has inherent delay on both the transmit and return
paths, and it would be a significant distraction to hear this audio back at the remote
site on delay.
As an example, if the IP audio latency between the remote site and the studio is
250ms, and the latency back from the studio is also 250ms, then the round-trip
delay is 500ms or half a second. If a mix minus was not created and remote site
announcers heard the full mix back from the studio, including their own audio, they
would hear themselves on a half second delay. This would create an ‘echo effect’ and
make it very difficult to maintain broadcasting.
In the early days a mix-minus was often fed via a telephone hybrid, but increasingly
these days it is fed over IP using devices like smartphone apps and audio codecs.
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