Fader Resource

Fader Resources are used in the AlphaCom System for providing clickfree audio switching between sources in group audio features.

Usage

One fader resource is used when activating one of the following functions:

• Groupcall - switch between gong tone and microphone, fade in/out when m-key is pressed/released.
• Simplex conference

In a MultiModule, one fader is needed in each participant module.

A fader is used along with two timeslots. The audio source is connected to the source timeslot. The fader loops the audio to the distribution timeslot. All listeners listen on the distribution timeslot. When switching sources, the fader fades out the source audio, and keep feeding the distribution timeslot during the switch. The listeners are not involved in the switch.

Realization

We use the otherwise unused SBI subchannel 0 of the Audio Scanners as Fader Resource. (All SBI Channel has a fader function on subchannel 0). The SBI subchannel is set in Loopback mode when used as Fader Resource.

Fader resources are found on these boards:

• AMC-IP: 12 faders (from AMC 10.31)
• ASLT: 2 faders
• ATLB-12: 4 faders
• ATLB: 2 faders

The AMC-IP board provides 12 fader resources, by using unused "SBI channels" realized by the FPGA. These faders limits the audio to 7 kHz bandwidth. The AMC SW will use SBI based faders if available, and fall back to FPGA faders if no SBI faders are available. For FPGA faders, audio is looped via the DSP. This is because treble deemphasis is done in FPGA, while the preempasis is done in DSP.

Also see: AlphaCom Audio Switching Hardware.