diff --git a/src/trx-core/src/audio.rs b/src/trx-core/src/audio.rs
index da9bf70..c833c68 100644
--- a/src/trx-core/src/audio.rs
+++ b/src/trx-core/src/audio.rs
@@ -59,6 +59,9 @@ pub const AUDIO_MSG_VCHAN_REMOVE: u8 = 0x11;
 /// Server → client: a virtual channel was destroyed server-side (e.g. went out of bandwidth).
 /// Payload: 16-byte UUID of the destroyed channel.
 pub const AUDIO_MSG_VCHAN_DESTROYED: u8 = 0x12;
+/// Client → server: update the audio filter bandwidth of an existing virtual channel.
+/// Payload: JSON `{"uuid": "<uuid>", "bandwidth_hz": <u32>}`.
+pub const AUDIO_MSG_VCHAN_BW: u8 = 0x13;
 
 /// Maximum payload size for normal messages (1 MB).
 const MAX_PAYLOAD_SIZE: u32 = 1_048_576;
diff --git a/src/trx-core/src/vchan.rs b/src/trx-core/src/vchan.rs
index 203a810..aeab095 100644
--- a/src/trx-core/src/vchan.rs
+++ b/src/trx-core/src/vchan.rs
@@ -95,6 +95,9 @@ pub trait VirtualChannelManager: Send + Sync {
     /// Update the demodulation mode of an existing channel.
     fn set_channel_mode(&self, id: Uuid, mode: &RigMode) -> Result<(), VChanError>;
 
+    /// Update the audio filter bandwidth of an existing channel.
+    fn set_channel_bandwidth(&self, id: Uuid, bandwidth_hz: u32) -> Result<(), VChanError>;
+
     /// Subscribe to decoded PCM audio from a channel.
     /// Returns `None` if the channel UUID does not exist.
     fn subscribe_pcm(&self, id: Uuid) -> Option<broadcast::Receiver<Vec<f32>>>;