This one will do it.
http://www.db-audioware.com/sidechain-compressor.html

http://www.kvraudio.com/get/1315.html
The freeware 'Slim Slow Slider Side Chain Compressor' allegedly works with Vegas,
there are other side chain comps that work w/ Vegas I have run across but can't find at the moment.


For stereo:
Input ch1: Signal input L
Input ch2: Signal input R
Input ch3: Key input L
Input ch4: Key input R
For mono:
Input ch1: Signal input
Input ch2: Key input
Other controls: ratio, attack, hold, release, knee, gain and key volume.

I'll give them a try, thanks!
How do you route audio in vegas to 3&4?

Jesse

I stand corrected, at least in regards to the db-audioware "Sidechain Compressor", which appears to have the ability to internally buss between instances inserted into different mixer channels. User is stuck with that flavour of compressor and any internal sidechain EQ. BTW the demo video on their website is excellent!

However the 'Slim Slow Slider Side Chain Compressor' has no chance to work in Vegas as it requires distinct 4-chan architecture within a mixer channel to side-chain correct e.g. 2 inputs for L/R signal, 2 inputs for sidechain signal; BTW it crashes Vegas if inserted into a 5.1 Master channel!

In general, the Vegas mixer is not well setup to do flexible sidechaining, because of it's limited channel & buss architecture, where user should have complete control of every aspect of the necessary sidechain signal.

It is possible with Wave Hammer also.
Got this from sony a long time ago.


Vegas 8 is able to set up pseudo side-chain compression/gate effects due to the new pan-linked bus sends and the flexibility of the Wave Hammer Surround plugin. Below are notes on the routing setups needed to simulate various side-chain situations.

The side-chain simulation is done by hard panning channels to busses, and having the Wave Hammer operate on either the left or right signal only. Then, the bus is panned so that the compressor source material is muted. Finally, in the case of mono compression, the signals are re-panned on additional busses so that they are
positioned in the center on final output.


1. Sidechain Ducking
Mono
Two tracks, three busses.
-Track 1 (foreground audio)
Pan: Hard Left - Pan mode: Constant Power
Bus A Send: 0dB - Link to main track pan activated
Main output: Bus C
-Track 2 (background audio)
Pan: Hard Right - Pan mode: Constant Power
Main output: Bus A
-Bus A
Volume: 0.0 dB
Pan: Hard Right - Pan mode: Constant Power
Main output: Bus B
Insert plugin: Wave Hammer Surround
Compressor Tab: Set compression parameters to desired ducking amount
Volume Maximizer Tab: Bypass
Routing tab:
Channel(s) to use for control signal: L only
Channel(s) to affect: All
-Bus B
Volume: 6.0 dB
Pan: 50% L - Pan mode: Add Channels (0 dB Center)
Main Output: Master
-Bus C
Volume: 6.0 dB
Pan: 50% R - Pan mode: Add Channels (0 dB Center)
Main Output: Master


2. Sidechain Ducking
Stereo


Four tracks, two busses.
-Track 1 (foreground audio, left channel)
Main output: Master
Pan: Hard Left - Pan mode: Constant Power
Bus B Send: 0 dB - Link to main track pan activated
-Track 2 (foreground audio, right channel)
Main output: Master
Pan: Hard Right - Pan mode: Constant Power
Bus A Send: 0 dB - Link to main track pan activated
-Track 3 (background audio, left channel)
Main output: Bus A
Pan: Hard Left - Pan mode: Constant Power
-Track 4 (background audio, right channel)
Main output: Bus B
Pan: Hard Right - Pan mode: Constant Power
-Bus A
Volume: 0.0 dB
Pan: Hard Left - Pan mode: Constant Power
Main output: Master
Insert plugin: Wave Hammer Surround
Compressor Tab: Set compression parameters to desired ducking amount
Volume Maximizer Tab: Bypass
Routing tab:
Channel(s) to use for control signal: R only
Channel(s) to affect: All
-Bus B
Volume: 0.0 dB
Pan: Hard Right - Pan mode: Constant Power
Main output: Master
Insert plugin: Wave Hammer Surround
Compressor Tab: Set compression parameters to desired ducking amount
Volume Maximizer Tab: Bypass
Routing tab:
Channel(s) to use for control signal: L only
Channel(s) to affect: All


3. Sidechain Project WH (simulation of original PEF project)

Two tracks, three busses.
-Track 1 (Compressor Listen Audio)
Volume: -1.2 - Volume envelope: -inf. dB over entire track
Pan: Hard Left - Pan mode: Constant Power
Bus A Send: 0dB - Link to main track pan activated
Main output: Bus C
-Track 2 (Compressed Audio)
Pan: Hard Right - Pan mode: Constant Power
Main output: Bus A
-Bus A
Volume: 0.0 dB
Pan: Hard Right - Pan mode: Constant Power
Main output: Bus B
Insert plugin: Wave Hammer Surround
Compressor Tab: Set compression parameters to desired ducking amount
Volume Maximizer Tab: Bypass
Routing tab:
Channel(s) to use for control signal: L only
Channel(s) to affect: All
-Bus B
Volume: 6.0 dB
Pan: 50% L - Pan mode: Add Channels (0 dB Center)
Main Output: Master
-Bus C
Volume: 6.0 dB
Pan: 50% R - Pan mode: Add Channels (0 dB Center)
Main Output: Master