Ducking System

The ducking function serves several purposes:

• It provides “aesthetic” control over the caller that many programmers prefer and allows the announcer to “override” the caller in a way that sounds natural and appropriate.

• It reduces feedback when the Hx is used as a speakerphone in an “open loudspeaker’” situation.

• It dynamically improves effective trans-hybrid loss to reduce leakage when necessary.

When the ducking function is enabled, the Hx inserts a controlled loss (reduction in gain) into whichever audio path (send or receive) is not active at the moment. When the caller is speaking, this loss is inserted in the announcer path; when the announcer is speaking, caller gain is reduced.

The effect is "seesaw-like" and normally, the amount of gain reduction is symmetrical. However, if Feedback Reduction is also enabled, the hybrid will have more ducking in the announcer-to-caller direction.

More ducking is typically necessary when using an open loudspeaker. As noted above, ducking helps prevent feedback and reduces the amount of echo returned to the caller.

Exactly how much of this effect is applied is selectable, from Half Duplex (which makes the hybrid operate like a "one-way-at-a-time" speakerphone) to Full Duplex (0 dB) which disables ducking altogether. The default setting is -6 dB.

Audio Processing and Ducking Signal Flow

Figure 1 below illustrates the signal processing chain in both the SEND input to the caller as well as the caller receive to the RCV output path. The ducking system is involved in both processing paths.

This figure also shows which processing stages are adjustable via the SETTINGS and OPTIONS bank of DIP switches in the rear of the hybrid unit. See the on DIP Switch settings for details.