ST-VP2 Automatic Ducking Module
The automatic ducking unit shall be an RDL ST-VP2. The unit shall provide two line-level inputs and one line-level output. One input shall be designated for music and one input shall be designated for voice. The unit shall sense audio at the voice input and automatically fade down the volume of the music for the duration that audio is present at the voice input. After completion of a detected voice message and subsequent defined delay, the unit shall fade up the volume of the music. The voice input shall be active when audio is detected and shall otherwise remain fully muted.

Each input shall be electronic balanced bridging with an input impedance no less than 20 kOhms and shall be fully compatible with either an unbalanced or balanced audio source. Normal rated operation and output from the unit shall be adjustable for an input level range of at least -20 dBu to +18 dBu.

Four continuously adjustable multi-turn trimming controls shall be provided. Two trimmers shall be provided to set the proper gain of the inputs. A corresponding LED indicator shall be provided to indicate the correct operating level for each input. One trimmer shall be provided to set the attenuation of the music during a voice announcement. One trimmer shall be provided to set the delay between the end of the detected voice announcement and the fade-up of the music source.

The unit shall provide an audio frequency response of 25 Hz to 20 kHz (± 1 dB) with total harmonic distortion plus noise of <0.02% (20 Hz to 20 kHz) and a noise floor exceeding 70 dB below the normal rated output level. The music input shall include an integral analog audio compressor/limiter with 18 dB of range, an attack time of 25 ms and a release time of 2.5 seconds.  The voice input signal detector shall trigger at 24 dB below the normal input operating level. The fade depth of the music input shall be adjustable from 0 dB to 25 dB and shall include a provision to duck the music input fully off.  The delay time between the end of the voice input detection and the subsequent fade-up of the music source shall be adjustable from 2 to 4 seconds.

The unit shall provide a line-level balanced audio output at a nominal rated output level of 0 dBu into a balanced 600 O load. The output circuit shall be configured to produce an unbalanced output of proper phase between the positive output leg and ground. 

The unit shall be constructed in an electrically non-conductive, thermally conductive enclosure. Internal circuitry shall be protected from moisture and vibration using a thermally conductive compound that permanently secures the circuitry within the enclosure.

The face of the unit shall provide graphical labels identifying wiring connections and operating controls. Indicators and controls shall be oriented toward the front edge of the unit.

Connection to external wiring shall be provided using a fixed terminal block on the edge of the unit. The terminal block shall accept wiring gauges from 14 to 22 and shall include a positive electrically conductive mechanism to prevent wire abrasion by the terminal screws.

The unit shall measure 3” (7.6 cm) x 1.6” (4 cm) x 0.7” (1.7 cm) and be compatible with all RDL STICK-ON mounting accessories. The unit shall be supplied with a two part re-closable polypropylene fastener system equipped with a rubber adhesive that bonds to low surface energy materials.

Power requirements shall be 24 Vdc ground-referenced with a maximum current not exceeding 35 mA. The unit shall utilize an external power supply. The unit shall be engineered, assembled and tested in the U.S.A. and be specified for continuous duty in professional installed systems. The unit shall be specified for operation in an ambient temperature between 0 and 55 degrees C. The unit shall comply with relevant EMC requirements and shall bear the CE marking.

The unit shall be an RDL ST-VP2.