diff --git a/scripts/filters.py b/scripts/filters.py
index a9daf50..763fca7 100644
--- a/scripts/filters.py
+++ b/scripts/filters.py
@@ -1,20 +1,35 @@
 
+import numpy as np
 from scipy.signal import butter, lfilter, decimate
 
 def anti_alias(data, sample_rate, max_frequency):
+    FILTER_HEADROOM = 1.2
     nyquist_rate = 2 * max_frequency
+    downsample_factor = 1
 
     if sample_rate > nyquist_rate:
-        filtered_data = lowpass_filter(data, max_frequency, sample_rate)
+        filtered_data = lowpass_filter(data, max_frequency * FILTER_HEADROOM, sample_rate)
 
         downsample_factor = int(sample_rate / nyquist_rate)
-
         filtered_data = decimate(filtered_data, downsample_factor)
         sample_rate = sample_rate // downsample_factor
     else:
         filtered_data = data
 
-    return filtered_data, sample_rate
+    return filtered_data, sample_rate, downsample_factor
+
+def smoothing_filter(data, window_size=256):
+    window = np.ones(window_size) / window_size
+    return np.convolve(data, window, mode='same')
+
+# Stolen from selcald
+def note(freq, length, amp=1.0, rate=44100):
+    if freq == 0:
+        data = np.zeros(int(length * rate))
+    else:
+        t = np.linspace(0, length, int(length * rate))
+        data = np.sin(2 * np.pi * freq * t) * amp
+    return data
 
 # These originally came from https://scipy.github.io/old-wiki/pages/Cookbook/ButterworthBandpass,
 # but they've been copied around the internet so many times that ChatGPT now produces them verbatim.
diff --git a/scripts/selcal-detect.py b/scripts/selcal-detect.py
index 72078a0..bcfafc8 100755
--- a/scripts/selcal-detect.py
+++ b/scripts/selcal-detect.py
@@ -5,85 +5,31 @@ import sys
 import numpy as np
 from scipy import signal
 from scipy.io import wavfile
-from scipy.signal import butter, lfilter
-
-
-tones = {}
-with open('tones.csv', newline='') as csvfile:
-    reader = csv.DictReader(csvfile)
-    for row in reader:
-        tones[row['designator']] = float(row['frequency'])
-
-'''
-def freq_of_key(midi_key):
-    return 440.0 * (2 ** ((midi_key - 69)/12))
-
-tones = {}
-for c in range(65, 90):
-    tones[c] = freq_of_key(c)
-'''
-
-# Shamelessly lifted from
-# https://scipy.github.io/old-wiki/pages/Cookbook/ButterworthBandpass
-def butter_bandpass(lowcut, highcut, fs, order=5):
-    nyq = 0.5 * fs
-    low = lowcut / nyq
-    high = highcut / nyq
-    b, a = butter(order, [low, high], btype='band')
-    return b, a
-
-def butter_bandpass_filter(data, lowcut, highcut, fs, order=5):
-    b, a = butter_bandpass(lowcut, highcut, fs, order=order)
-    y = lfilter(b, a, data)
-    return y
-
-# tone synthesis
-def note(freq, cycles, amp=32767.0, rate=44100):
-    len = cycles * (1.0/rate)
-    t = np.linspace(0, len, int(len * rate))
-    if freq == 0:
-        data = np.zeros(int(len * rate))
-    else:
-        data = np.sin(2 * np.pi * freq * t) * amp
-    return data.astype(int)
-
-def decimate_from_sample_rate(sample_rate):
-    if sample_rate == 44100:
-        return 4  # rate = 11025, Fmax = 5512.5 Hz
-    elif sample_rate == 48000:
-        return 5  # rate = 9600, Fmax = 4800 Hz
-    elif sample_rate == 22050:
-        return 2  # rate = 11025, Fmax = 5512.5 Hz
-    elif sample_rate == 11025:
-        return 1  # rate = 11025, Fmax = 5512.5 Hz
-    else:
-        raise ValueError("Sample rate not supported")
+from tones import TONES
+from filters import bandpass_filter, note, smoothing_filter, anti_alias
 
+pure_sample_length = 0.1
 
 if __name__ == '__main__':
-    # TODO JMT: What is this?
-    FLT_LEN = 2000
-
     file_name = sys.argv[1]
     sample_rate, data = wavfile.read(file_name)
-
     print(f"{file_name}: {len(data)} samples @ {sample_rate} Hz")
 
-    decimate = decimate_from_sample_rate(sample_rate)
-    if decimate > 1:
-        data = signal.decimate(data, decimate)
-        sample_rate = sample_rate / decimate
+    if len(data.shape) == 2:
+        data = data.mean(axis=1)
 
-    print(f'Length after decimation: {len(data)} samples')
+    # Normalise
+    print(np.max(data))
+    data = data / np.max(data)
 
-    data = butter_bandpass_filter(data, 270, 1700, sample_rate, order=8)
+    # TODO JMT: Find out why the correlation step fails when max frequency <= 2 * nyquist rate
+    data, sample_rate, decimation = anti_alias(data, sample_rate, 4800)
+    print(f'Length after decimation: {len(data)} samples (/{decimation}, {sample_rate})')
 
-    pure_signals = {tone:note(freq, FLT_LEN, rate=sample_rate) for tone,freq in tones.items()}
+    pure_signals = {tone:note(freq, pure_sample_length, rate=sample_rate) for tone,freq in TONES.items()}
     correlations = {tone:np.abs(signal.correlate(data, pure, mode='same')) for tone,pure in pure_signals.items()}
+    massaged = {tone:smoothing_filter(correlation) for tone,correlation in correlations.items()}
 
-    N = FLT_LEN // 8 # Rolling average length
-    cumsum_convolution = np.ones(N)/N
-    massaged = {tone:np.convolve(correlation, cumsum_convolution, mode='valid') for tone,correlation in correlations.items()}
 
     # Only import if we're actually plotting, these imports are pretty heavy.
     import pyqtgraph as pg
@@ -100,7 +46,7 @@ if __name__ == '__main__':
     legend.setParentItem(legend_view)
 
     color_map = pg.colormap.get('CET-C6s')
-    colors = color_map.getLookupTable(nPts=len(tones))
+    colors = color_map.getLookupTable(nPts=len(TONES))
 
     for (tone, correlation), color in zip(massaged.items(), colors):
         line = plot.plot(correlation, pen=pg.mkPen(color=color), fillLevel=0.1, name=tone)