diff --git a/amodem/calib.py b/amodem/calib.py
index 471b44e..299f5fb 100644
--- a/amodem/calib.py
+++ b/amodem/calib.py
@@ -20,20 +20,17 @@ def volume_controller(cmd):
     return controller if cmd else (lambda level: None)
 
 
-def send(config, dst, volume_cmd=None):
+def send(config, dst, volume_cmd=None, gain=1.0, limit=None):
     volume_ctl = volume_controller(volume_cmd)
     volume_ctl(1.0)  # full scale output volume
 
     calibration_symbols = int(1.0 * config.Fs)
     t = np.arange(0, calibration_symbols) * config.Ts
-    signals = [np.sin(2 * np.pi * f * t) for f in config.frequencies]
+    signals = [gain * np.sin(2 * np.pi * f * t) for f in config.frequencies]
     signals = [common.dumps(s) for s in signals]
 
-    try:
-        for signal in itertools.cycle(signals):
-            dst.write(signal)
-    except KeyboardInterrupt:
-        pass
+    for signal in itertools.islice(itertools.cycle(signals), limit):
+        dst.write(signal)
 
 
 def frame_iter(config, src, frame_length):
@@ -70,13 +67,13 @@ def detector(config, src, frame_length=200):
 
         success = all(flags)
         if success:
-            message = 'good signal'
+            msg = 'good signal'
         else:
-            message = 'too {0} signal'.format(errors[flags.index(False)])
+            msg = 'too {0} signal'.format(errors[flags.index(False)])
 
         yield common.AttributeHolder(dict(
             freq=freq, rms=rms, peak=peak, coherency=coherency,
-            total=total, success=success, message=message
+            total=total, success=success, msg=msg
         ))
 
 
@@ -103,17 +100,29 @@ def volume_calibration(result_iterator, volume_ctl):
             yield result
 
 
+def iter_window(iterable, size):
+    block = []
+    while True:
+        item = next(iterable)
+        block.append(item)
+        block = block[-size:]
+        if len(block) == size:
+            yield block
+
+
 def recv(config, src, verbose=False, volume_cmd=None):
-    fmt = '{0.freq:6.0f} Hz: {0.message:20s}'
+    fmt = '{0.freq:6.0f} Hz: {0.msg:20s}'
     if verbose:
         fields = ['total', 'rms', 'coherency', 'peak']
         fmt += ', '.join('{0}={{0.{0}:.4f}}'.format(f) for f in fields)
 
-    result_iterator = detector(config=config, src=src)
     volume_ctl = volume_controller(volume_cmd)
 
-    try:
-        for result in volume_calibration(result_iterator, volume_ctl):
-            log.info(fmt.format(result))
-    except KeyboardInterrupt:
-        pass
+    result_iterator = detector(config=config, src=src)
+    result_iterator = volume_calibration(result_iterator, volume_ctl)
+    result_iterator = iter_window(result_iterator, size=3)
+    for r in result_iterator:
+        # don't log errors during frequency changes
+        if r[0].success and r[2].success and r[0].freq != r[2].freq:
+            r[1].msg = r[1].msg if r[1].success else 'frequency change'
+        log.info(fmt.format(r[1]))
diff --git a/tests/test_calib.py b/tests/test_calib.py
index fc1e61a..ceedd86 100644
--- a/tests/test_calib.py
+++ b/tests/test_calib.py
@@ -6,6 +6,7 @@ config = config.fastest()
 from io import BytesIO
 
 import numpy as np
+import random
 import pytest
 import mock
 
@@ -26,9 +27,8 @@ class ProcessMock(object):
         pass
 
     def write(self, data):
+        assert self.buf.tell() < 10e6
         self.buf.write(data)
-        if self.buf.tell() > 1e6:
-            raise KeyboardInterrupt
 
     def read(self, n):
         return self.buf.read(n)
@@ -36,24 +36,53 @@ class ProcessMock(object):
 
 def test_success():
     p = ProcessMock()
-    calib.send(config, p)
+    calib.send(config, p, gain=0.5, limit=32)
     p.buf.seek(0)
     calib.recv(config, p)
 
 
+def test_too_strong():
+    p = ProcessMock()
+    calib.send(config, p, gain=1.001, limit=32)
+    p.buf.seek(0)
+    for r in calib.detector(config, src=p):
+        assert not r.success
+        assert r.msg == 'too strong signal'
+
+
+def test_too_weak():
+    p = ProcessMock()
+    calib.send(config, p, gain=0.01, limit=32)
+    p.buf.seek(0)
+    for r in calib.detector(config, src=p):
+        assert not r.success
+        assert r.msg == 'too weak signal'
+
+
+def test_too_noisy():
+    r = random.Random(0)  # generate random binary signal
+    signal = np.array([r.choice([-1, 1]) for i in range(int(config.Fs))])
+    src = BytesIO(common.dumps(signal * 0.5))
+    for r in calib.detector(config, src=src):
+        assert not r.success
+        assert r.msg == 'too noisy signal'
+
+
 def test_errors():
     class WriteError(ProcessMock):
         def write(self, data):
             raise KeyboardInterrupt()
     p = WriteError()
-    calib.send(config, p)
+    with pytest.raises(KeyboardInterrupt):
+        calib.send(config, p, limit=32)
     assert p.buf.tell() == 0
 
     class ReadError(ProcessMock):
         def read(self, n):
             raise KeyboardInterrupt()
     p = ReadError()
-    calib.recv(config, p, verbose=True)
+    with pytest.raises(KeyboardInterrupt):
+        calib.recv(config, p, verbose=True)
     assert p.buf.tell() == 0