This read-only INTEGER indicates which tone frequency (none, 1950Hz, or 2175Hz) should be filtered out from the radio input for this voice class. Administrators use it to confirm that a specific LMR signaling tone frequency, often used by radio squelch or signaling systems, is being filtered from the audio path as configured. For example, if unwanted signaling tone bleed-through is heard on an LMR interconnect, checking this object confirms whether the correct filter frequency was actually applied for that voice class.