i tried listening to a radio microphone. The signal was in zero span mode very bad with a lot of hiss. Is this normal?
best regards
Patrick
Wireless mics usually have proprietary compander schemes, where the audio signal is heavily compressed before transmitting, often with pre-emphasis that effectively boosts the high end. When you receive the signal with hardware that doesn't expand and de-emphasize the signal, you'll hear tinny sounding audio.
The expansion threshold and ratio must be exactly as the manufacturer prescribes for normal operation. Each mfg. uses slightly different schemes, with variations from model to model. Sennheiser's 3000 series receivers allow you to switch compander schemes for compatibility with their different transmitter models, and Shure's UR series RX can change compander schemes for use with 900/1000 IEM TX in point-to-point mode.
It is highly unlikely that 3rd party measurement instruments will have RX companding capability of any kind, let alone the correct prescriptions for the multitude of pro audio TX's. The listen function is generally useful to determine if there is severe interference occurring, and little more. There are exceptions, though. I've found that by adjusting a Signal Hound's software HF filter settings in its listen function, you can get acceptable sounding reception for monitoring Telex BTR series and other mono TX com systems.