dBu is an absolute measurement. 0dBu is referenced to 0.775 volts RMS
Headset Microphone Input
Input Type: Dynamic, Electret
Input Impedance: 1kΩ
Max Input Level: -60dBu to -40dBu switchable
Headset Output
Load Impedance: >= 4Ω
Output Impedance: 47Ω
Output Limiter Threshold: -4dBu, + 3dB
Max Output Level Before Distortion: -4dBu
Partyline Output
Off Noise: <-80dBu
Output Impedance: >10kΩ
Maximum Output: -4dBu
Partyline Input
Maximum Level Before Clipping: +3dBu
Sidetone Null Capability: >25dB
Frequency Response
Dynamic Mic - Partyline: 40Hz - 22kHz, + 3dB
Dynamic Mic - Line Out: 20Hz - 22kHz, + 3dB
Dynamic Mic - 4-Wire Out: 100Hz - 22kHz, + 3dB
IFB Input - Headset Out: 100Hz - 22kHz, + 3dB
Partyline - Headset Out: 150Hz - 22kHz, + 3dB
Max Distortion Dynamic Mic - Partyline: <0.1%
Dynamic Mic - Line Out: <0.05%
IFB Input - Headset Out: <0.5%
Partyline - Headset Out: <0.1%
Noise
Dynamic Mic - Partyline: <-75dBu
Dynamic Mic - Line Out: <-85dBu
IFB Input - Headset Out: <-65dBu
Partyline - Headset Out: <-65dBu