Audio-Technica M3 Handbuch Seite 12

How to select a frequency
Note: Because these frequencies are shared with TV broadcasting
(depending on country of use), frequency selection is largely
dependent upon which TV broadcast channels are in operation
where the wireless system is to be used.
Squelch Control
(continued)
Setting Levels
(no attenuation)
Aux In jack
Aux Level
(Receiver)
Note: If you connect a stereo source (such
as an MP3 player) into the M3R Stereo Receiver's Aux Input,
be certain to use a mono adapter to protect your equipment
from the DC voltage that is applied to the ring of the stereo
connector.
Trim Control
0
Mic Vol
Aux Level