diff --git a/lib/usbif/__init__.py b/lib/usbif/__init__.py
index 9893321..f756059 100644
--- a/lib/usbif/__init__.py
+++ b/lib/usbif/__init__.py
@@ -222,9 +222,14 @@ def _close(self):
         pass
 
     def _check(self, want):
+        # Two comparisons rather than `in (want, INOUT)`: the tuple is built
+        # on every call, and read() is polled every few milliseconds by apps
+        # that also move audio, where the garbage it leaves forces a
+        # collection (tens of milliseconds on a large heap) every second or so.
         if not self.is_open:
             raise OSError("MIDI port is closed")
-        if self.direction not in (want, INOUT):
+        direction = self.direction
+        if direction != want and direction != INOUT:
             raise OSError(
                 "MIDI port {!r} is {}-only".format(self.info.name, self.direction)
             )
diff --git a/lib/usbif/native_usb.py b/lib/usbif/native_usb.py
index bab4d72..6aeee1c 100644
--- a/lib/usbif/native_usb.py
+++ b/lib/usbif/native_usb.py
@@ -346,15 +346,20 @@ def uac_pump_rate(self, *args):
         rate the pump's I2S wire is clocked at, and how often it followed."""
         return _require().uac_pump_rate(*args)
 
-    def uac_available(self, *args):
-        return _require().uac_available(*args)
+    # uac_available() and uac_read() take fixed arguments, unlike the
+    # wrappers around them: they are what a Python pump polls every
+    # millisecond, and `*args` builds a tuple per call. That garbage forces a
+    # collection every so often, which on a large heap stalls the pump for
+    # longer than the 4.7 ms the full-speed FIFO holds.
+    def uac_available(self):
+        return _require().uac_available()
 
     def uac_volume(self, *args):
         """The host's playback volume and mute, as the host set them."""
         return _require().uac_volume(*args)
 
-    def uac_read(self, *args):
-        return _require().uac_read(*args)
+    def uac_read(self, buf=None):
+        return _require().uac_read(buf)
 
     def uac_stats(self, *args):
         return _require().uac_stats(*args)