What is Instrument Level?

Instrument level signals represent the audio signal strength generated from musical instruments. Generally, these are stronger than microphone levels but reside in a middle-ground between line level and mic level signals. They also have a high-impedance characteristic, meaning they have high output impedance and very low current relative to the output voltage.

the difference between Pro line level and Consumer line level

Pro line level and consumer line level are designed for different applications and requirements. Pro line level is suited for high-impedance and long-distance transmission, using balanced signal transmission. Consumer line level is optimized for short-distance unbalanced signal transmission and is relatively less expensive to manufacture.

What is Pro line level?

In pro line levels, +4dBu is commonly used as the reference level.
+4dBu corresponds to a signal level based on 1.228V, and it is the standard signal strength commonly used among professional audio equipment. Transmitting at levels higher than this would be inefficient due to excessive power consumption of the preamplifier, and transmitting at lower levels may result in signal degradation due to the typical impedance of XLR or TRS cables.