bat wrote:but it just quiets all the rest (in the middle) wonder why?
One of the time settings is probably too long. Try starting with all the time settings at zero, then work from there.
Typically you would just use ducking against a strong beat that is not too fast, for example a kick drum or a thumping bass beat. You wouldn't tend to use it against a full drum mix as that would just make the ducking jump around all over the place and sound messy (not what you're after).
It's easiest to hear what's happening if you have the duck amount quite high to start with (say -12 to -18 dB).
I would start with the attack and release times (in the case of Audacity's Auto Duck these are made up of 5 time settings) very fast (try zero as suggested).
Then adjust the threshold so that it ducks on the peaks of the beat. If the threshold is too high (above the level of the beat) then nothing will happen. If it is too low, then the ducking will be triggered by background noise and ringing / sustain rather than the beat itself and it will duck continuously.
Once you have the threshold set right, you can gradually relax the time values to get a smoother response.
With the Audacity Auto Duck, increasing the outer fade time a little will give a bit more space for the beat to come through. Increasing the inner fade time a little will make the effect more subtle by creating an overlap between the beat and the sound that is ducking. Too long on any setting will loose the effect altogether by either ducking everything or ducking nothing.
The Maximum pause (hold) needs to stay very short - say around 0.01 to 0.05 seconds (10 to 50 milliseconds). If this is too long it won't work. If it is too short and you are using a bass track as the trigger then you can get the ducking being triggered by the wave peaks rather than the beat. (Actually, I don't think the Audacity will go that fast, so you are probably protected from that problem even with the Maximum Pause set to zero, but it can be an issue with other software or hardware devices).
When you have your time and threshold set, you can then adjust the "Amount" according to taste (you may also want to tweak the attack and decay times a just little as you adjust the amount).
With a real side-chain compressor you can get a bit fancier by Eq'ing both the trigger and processed signal paths, then mixing the processed signal back in with the original. If you want to get really fancy you can also do this with Audacity by making duplicates of your tracks, then muting the Eq'd trigger track after the effect has been used and adjusting the volume sliders of the processed track and it's original version, but this gets quite complicated and not easy to do without real-time processing.
I think i will if i can't find another way...