diff --git a/modem/arq_session_iss.py b/modem/arq_session_iss.py
index c33144f5..b56a7032 100644
--- a/modem/arq_session_iss.py
+++ b/modem/arq_session_iss.py
@@ -26,7 +26,7 @@ class ARQSessionISS(arq_session.ARQSession):
     # DJ2LS: 3.5 seconds is working well WITHOUT a channel busy detection delay
     TIMEOUT_CHANNEL_BUSY = 0
     TIMEOUT_CONNECT_ACK = 3.5 + TIMEOUT_CHANNEL_BUSY
-    TIMEOUT_TRANSFER = 3.5 + TIMEOUT_CHANNEL_BUSY
+    TIMEOUT_TRANSFER = 2.0 + TIMEOUT_CHANNEL_BUSY
     TIMEOUT_STOP_ACK = 3.5 + TIMEOUT_CHANNEL_BUSY
 
     STATE_TRANSITION = {
diff --git a/modem/modem.py b/modem/modem.py
index 38a79f56..a5f6b393 100644
--- a/modem/modem.py
+++ b/modem/modem.py
@@ -162,7 +162,7 @@ class RF:
                 callback=self.sd_output_audio_callback,
                 device=out_dev_index,
                 samplerate=self.AUDIO_SAMPLE_RATE,
-                blocksize=600,
+                blocksize=256,
             )
             self.sd_output_stream.start()