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166/266xs Sidechain Input Questions

PGR50PGR50 Posts: 3
edited January 2013 in Connectivity
Hi everyone! I have a 166xs and a 266xs and I want to use one of them to duck stereo background music when someone speaks into a mic and my question is about connecting a mono send into the sidechain inputs. When an Alesis 3630's channels are linked in stereo mode you can duck both channels with just one send into a single sidechain input by plugging a blank (unconnected) TS or TRS plug into the unused sidechain jack to disconnect that channel's input from the detection circuit.

Can the same thing be done with the 166xs and 266xs or will I have to connect the mono send to both sidechain inputs? Obviously the Stereo Couple feature will be active and I assume I'll need to turn on SC Enable for both channels.

Also, the explanation of the sidechain jack says "The RING acts as a Send, carrying a buffered version of the signal present at the 166xs INPUT jack, at an impedance of 2kΩ." Can someone explain in a little more detail what "buffered" means in this application and what a send like that would be used for?

Thank you,



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    PGR50PGR50 Posts: 3
    Here's the answer to my own question:

    I also sent this question to the dbx Tech Support Department via the form found in the Support tab in their website and received the following response from Travis (thanks, Travis!):
    You are correct. You will need to have both channels sidechain enable button pressed, and you will need to either run the sidechain signal to both channels or place an unused or dummy connector into the sidechain insert jack to activate the sidechain trigger. Then with the stereo couple button engaged the compressor will duck both channels depending on how channel one is set. Let me know if you need more help setting this up.
    I've also verified this with my own experimentation. My "announcer" setup includes a laptop running MediaMonkey to provide background music, a pair of wireless microphones (1 handheld and one headset), a mixer, and at least 1 dual-channel compressor. The laptop is patched directly into the inputs on the compressor with a stereo Y cable (1/8" TRS to dual 1/4" TS) and the outputs of the compressor are patched into the L/R line inputs of a stereo channel on the mixer with 1/4" TRS cables. The microphones are plugged into individual mono channels via XLR and I'm using the pre-fader buss (mono) as the sidechain send which is patched into the compressor's channel 1 sidechain jack via a 1/4" TS cable. Finally, I have an unused 1/8" TS to 1/4" TS adapter plugged into the channel 2 sidechain jack (more on this later).

    To use the system I simply turn up the pre-fader buss control on each mic channel I want to duck the background music with. Needless to say I leave that control turned all the way down on the music channel because I don't want the music ducking itself. I'm still experimenting with various compressor and mixer settings, but I'm quite satisfied with the results. But I've only used headphones during my experimentation so far and I'm sure my settings will have to change when I start using active speakers, so I'm not prepared to share any control settings yet.

    Here's an interesting observation about the blank plug in the channel 2 sidechain insert: The sidechain jacks on the 166 & 266 are TRS which (in addition to providing input via the TIP) also supply a send carrying a buffered version of the signal present at the 166xs INPUT jack on the RING. The user's manual says "You can also drive the 166xs SIDECHAIN INSERT with the output of most equipment, by using a 1/4� mono phone plug", but I noticed a subtle difference in the output level of channel 2 when I switched between blank TS and TRS plugs in the sidechain jack. With a blank TRS plug the ducking effect on the two channels seemed asymmetric, but with a TS plug the ducking effect seemed more symetric.

    The conclusion I've come to is that shorting the RING to the SHIELD in the sidechain jack (with a TS plug) attenuates the music signal a little, but it was subtle enough that it may not even be apparent through speakers. The truth of the matter is it was subtle enough that the difference might be a product of my imagination, but I think not. Regardless, I've decided that I'll be using a TS blank in the channel 2 sidechain jack if I'm using a TS input cable in the channel 1 sidechain jack. I'll add that I'm using the 1/8-1/4" TS adapter for a blank because it was convenient.

    On a final note, I'll be replacing the 166xs with a 266xs in the music ducking role and using the 166sx in the microphone paths. About the only difference in setup will be that the 266xs won't have SC Enable buttons to push, but otherwise the setup and functionality should be the same for both units, at least when used in this application.

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    When I first tried this, the compressor would do exactly the opposite of what was expected. Each time the narrator (voice) would say something, the compressor would mute the music track! Here's what I found works:

    Behringer x1622usb mixer
    dbx 166 xs compresor
    Rode NT1-A Mic

    dbx 166xs front panel settings:
    Stereo link ON
    Channel 1 SC enable ON
    Channel 2 SC enable ON
    Expander/Gate Threshold = 3 notches above off. Turn clockwise until green light stays on while MIC is open. If using a recoded voice, a small amount of background noise behind the voice over is desirable to keep the gate from closing.
    Expander/Gate Release Slow
    Compressor Threshold -32db
    Overeasy ON
    Auto ON
    Output Gain +4
    Limiter +5

    dbx 166xs Back Panel Inputs:
    Channel 1 and 2 Inputs from background music source
    Channel 1 SC input from preamped MIC source (use a send from the mixer for this)
    Channel 2 SC input - plug in an unused unconnected TR plug or TR adapter

    Alternatively for Channel 1 SC input: If you have pre-recordeed voice material, connect a
    pre-recorded voice track with line level output (from a computer, ipod or other line level source)
    with y adapter. Plug ONE output from the y adapter into the sidechain input of channel 1
    on the compressor and the other output from the y adapter to a mono line input on the mixer.
    Set mixer to 0db for this input. If you have additional sends on your mixer, you could do it that way.

    dbx 166sx Back Panel Outputs:
    Connect Ch1 and Ch2 outputs to stereo line inputs on mixer board and set mixer to 0 db for these.

    On the mixer: Set the MIC and stereo line inputs to SUB. If using a y-adapter, set that mixer input to SUB also then use the SUB controls to set levels. Set the send output levels on the MIC and AUX SEND 1 to about 3/4 of the way up.

    You will need to play with the Expander/Gate Threshold setting to get this to work just right. Hope this helps someone.
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