This is a simple script that brings up a Yad interface when I plug in my USB audio card. The interface then activates JACK. JACK is then killed when I remove the card. You won't be able to do this for a normal user through Udev, since it is a root process. This script is run from the autostart section of my window manager (JWM).

start-JACK-on-USB-insert

#!/bin/bash
#you will need to modify the device names for JACK...
choose_params() {
	qy=$(yad --form --item-separator="|" --field "Purpose:CB" "CD|Live|HD")
	jackparams=$(echo $qy | awk -F '|' '{print $1}')
	case $jackparams in
	CD)
	jackd -dalsa -r44100 -p4096 -n3 -D -dhw:Device &
	export JACK_SAMPLE_RATE=44100
	export JACK_SETTING="REC"
	;;
	HD)
	jackd -dalsa -r48000 -p4096 -n3 -D -dhw:Device &
	export JACK_SAMPLE_RATE=48000
	export JACK_SETTING="HD"
	;;
	Live)
	jackd -R P88 -dalsa -r96000 -p64 -n2 -s -S -D -dhw:Device &
	export JACK_SAMPLE_RATE=48000
	export JACK_SETTING="LIVE"
	;;
	esac
	}

while true; do
 inotifywait -m /dev/snd/ -e create -e delete | while read dir action card; do
#this could probably be better implemented to work on a wider range of systems
  if [ $card == "controlC1" ]; then
   if [ $action == "CREATE" ]; then
   sleep 2
   choose_params
   elif [ $action == "DELETE" ];then
   pkill -9 jackd 
   unset JACK_SAMPLE_RATE
   unset JACK_SETTING
   fi
  fi
 done
done

You may be wondering about the sample rate numbers. This script was written for my system and a cheap Xenta Sound Pocket.

No matter what I don't record at 96kHz because it REALLY doesn't matter. Our ears can theoretically perceive frequencies up to around 22kHz; and Nyquist still applies. If the sample rate is higher than about 50kHz, you're recording things that cannot be heard and may not be perceived. If your sound "is better" at 96kHz it's because all the distortion that you were getting at lower sample rates has been pushed into a frequency range that you cannot hear. The quality of the hardware that is more important than the sample rate. There will (of course) be people who say "no, but [fill in anecdote showing how much of an audiophile they are here]" but belief is a powerful thing that drives us all to odd conclusions.

But the sound card I have has lower latency when I trick it into duplexing at 96kHz. This makes it much better for live looping and audio processing.

If the numbers upset you, just change the numbers to suit you.