Cleanfeeds, N-1, foldback, outside source return, cough signal:
There is a lot of confusion mainly about the names of the same kind of signals so let’s take a closer
look:
CLEANFEED or N-1 or OUTSIDE SOURCE:
Basically this is the (mono) signal that goes back to a caller into a telephone hybrid. The signal
consists of a mix of all signals in a program MINUS the signal that comes FROM the hybrid INTO the
channel of the mixing desk. This signal from the hybrid back into the mix will cause a feedback and
that is something we do not want. In radio broadcast mixing desks this signal can be a separate POST
FADE AUX bus without the incoming signal from the hybrid.
In some analog mixing desks this is not a separate bus but the signal is made from the total sum and
mixing this with a phase reversed version of the unwanted signal. This is OK as long as it is limited in
frequency range so it is mainly used for telephone hybrids.
Also upon switching on the TalkBack the signal is replaced by the microphone signal in order to talk to
the caller off air without the public hearing this conversation. If the damping of the hybrid allows this
can also be done on-air.
In the D4 a dedicated STEREO full bandwidth AUX bus is used for this purpose. Other than only
hybrids also full bandwidth stereo communication devices can be used (ISDN Codec).
With this system you can also couple 2 or more D4 mixing desks in separate rooms together without
the danger of feedback.
A special mode is putting the AUX-es in “pre-fader mode”, this allows incoming callers to talk to each
other off-air: CONFERENCE mode. This can be useful when 2 or more reporters are active that need
to know about each others activities. However they should be aware when they are on and off-air!
HEADPHONES FOLDBACK:
The signal that is fed to the headphones of a presenter. Basically the total mix of the main signal.
In order to allow the technician behind the mixing desk to talk to the presenter this signal is replaced
by the microphone signal if the TalkBack button is pushed.
With the D4 an AUX bus is used for this purpose and you can even built a dedicated mix e.g. lower
volume of the music contributions. It is not a cleanfeed signal as the presenter headphones needs the
own signal back to hear his/her own voice!
COUGH:
The cough signal is engaged with a pushbutton in the studio. Pushing this button switches the
microphone off the main mix and switches on the pfl. In this way the presenter can talk to the
technician off- air. In the D4 you can connect an external switch to one GPI and select both “mute”
and “remote pfl” of the microphone channel to the same GPI. If an external “mute” is applied the
START button LED will blink slowly.
Eela Audio D4 manual
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