T12 input...does the "instrument" switch trigger any different impedance or levels in the insert jack?
Assume you're referring to Input 1 & Input 2, and not Track 12?
A typical electric guitar has an impedance of 40kOms. The instrument impedance switch converts the input to a very high 1M Ohms to adjust for the guitar's impedance.
OM Spec Page:
LINE (BAL)/INST input jacks (1-6)
Connectors: 6.3mm (1/4”) standard TRS jacks
(Tip: HOT, Ring: COLD, Sleeve: GND)
Maximum input level: +22 dBu (LINE)/19.8 dBV (INST)
Nominal input level: +4 dBu (LINE)/ 1.8 dBV (INST)
Gain adjustment range: -10 - +40 dB
Input impedance: 22 kΩ (LINE)/1 MΩ (INST)
L/MONO(BAL)/INST input jacks (7, 9)
Connectors: 6.3mm (1/4”) standard TRS jacks
(Tip: HOT, Ring: COLD, Sleeve: GND)
Maximum input level: +22 dBu (LINE)/19.8 dBV (INST)
Nominal input level: +4 dBu (LINE)/ 1.8 dBV (INST)
Gain adjustment range: -20 - +30 dB
Input impedance: 18 kΩ (LINE)/ 1 MΩ (INST)
R (BAL) input jacks (8, 10)
Connectors: 6.3mm (1/4”) standard TRS jacks
(Tip: HOT, Ring: COLD, Sleeve: GND)
Maximum input level: +22 dBu
Nominal input level: +4 dBu
Gain adjustment range: -20 - +30 dB
Input impedance: 18 kΩ
INSERT jacks (1-2)
Connectors: 6.3mm (1/4”) standard TRS jacks
(Tip: SEND, Ring: RETURN, Sleeve: GND)
RETURN (Ring)
Nominal input level: 0 dBu
Maximum input level: +18 dBu
Input impedance: 5 kΩ
SEND (Tip)
Nominal output level: 0 dBu
Maximum output level: +18 dBu
Output impedance: 100 Ω