Manual

6
EarShot IFB does not offer studio-side audio output functionality. No output ports to hear callers are provided.
By default, EarShot IFB is a “one-to-many” device that sends only its own feed audio to callers. Callers can, via
DTMF, enable their source audio to be added to the mix (to send to other callers on that feed). This creates a
conferencing function.
Also by default, incoming callers are placed into a “waiting room” until they input a PIN for a specific feed. As an
option, Feed 3 can be chosen to be the “waiting room” feed before any PIN is sent by the caller.
EarShot IFB interfaces only to Voice-over-IP (VoIP) telephone circuits. These virtual phone lines are provided to
EarShot IFB over its Ethernet connection. VoIP phone lines can be delivered from cloud-based VoIP providers, VoIP-
based PBXs (in many cases), and via hardware gateways devices that bridge legacy phone circuits (e.g. T1/E1,
POTS) to VoIP. Separate setup menus are available for each of these. EarShot IFB interfaces to VoIP services using
the SIP protocol.
EarShot IFB can interface to most normal calls using standard telephony audio encoding (G.711). In some
circumstances, EarShot IFB can deliver audio to “pure” end-to-end VoIP callers with higher fidelity, using encoders
like G.722 and Opus.
EarShot IFB can handle thirty calls from standard telephone sources, spread across one, two, three, or four audio
feeds. It can handle up to ten simultaneous high fidelity feeds to VoIP callers. It can also handle a mix of both, at
varying capacities.
EarShot IFB is housed in a 1U 19” rackmount mainframe chassis. Level of each feed is displayed on front panel
LEDs. The mainframe serves a web page that provides all controls and configuration. Initial setup requires use of
the Comrex Device Manager software utility.
About Mix-Minus
Comrex support spends a lot of time discussing mix-minus, as it is not an obvious concept. In studio telephony
integration, there is a golden rule: People connecting from outside the studio must never be sent their own audio
back to themselves. If this rule is not followed, the result will be an unpleasant echo in the caller’s ear. It is the
responsibility of the studio tech to connect a feed to each feed on EarShot IFB that is a mix of all important audio
sources--in-studio mics, spots, automation etc., minus the caller. Of course, this is only true for EarShot IFB listeners
who are “on-air”. Producers, camera operators and others can monitor the full program feed. That’s why EarShot
IFB’s selectable feeds are so useful.