Fix chebyshev band pass and band stop returning all NaN

.github/workflows/run_unix.yml

@@ -354,6 +354,8 @@ jobs:
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/transforms.py
     - name: Downsampling Python
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/downsampling.py
+    - name: Chebyshev Band Filters Python
+      run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/chebyshev_band_filters.py
     - name: ICA Python
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/ica.py
     - name: CSP Python

python_package/examples/tests/chebyshev_band_filters.py

@@ -0,0 +1,56 @@
+import numpy as np
+
+from brainflow.data_filter import DataFilter, FilterTypes
+
+SAMPLING_RATE = 256
+PASS_FREQ = 10.0
+STOP_FREQ = 50.0
+CENTER_LOW = 5.0
+CENTER_HIGH = 15.0
+ORDER = 4
+RIPPLE = 1.0
+
+
+def amplitude_at(signal, freq):
+    spectrum = np.abs(np.fft.rfft(signal)) * 2 / len(signal)
+    return spectrum[int(round(freq * len(signal) / SAMPLING_RATE))]
+
+
+def main():
+    samples = SAMPLING_RATE * 4
+    t = np.arange(samples) / SAMPLING_RATE
+    # One tone inside the 5 to 15 Hz band and one well outside it.
+    signal = np.sin(2 * np.pi * PASS_FREQ * t) + np.sin(2 * np.pi * STOP_FREQ * t)
+
+    assert np.isclose(amplitude_at(signal, PASS_FREQ), 1.0, atol=0.01)
+    assert np.isclose(amplitude_at(signal, STOP_FREQ), 1.0, atol=0.01)
+
+    # Chebyshev type 1 band pass and band stop take five design parameters and expect the
+    # ripple after the band width. Writing it into slot 3 overwrote the band width, which
+    # produced an unusable design and an all-NaN output.
+    for name, apply_filter, kept, removed in (
+        ('bandpass', DataFilter.perform_bandpass, PASS_FREQ, STOP_FREQ),
+        ('bandstop', DataFilter.perform_bandstop, STOP_FREQ, PASS_FREQ),
+    ):
+        filtered = np.copy(signal)
+        apply_filter(
+            filtered,
+            SAMPLING_RATE,
+            CENTER_LOW,
+            CENTER_HIGH,
+            ORDER,
+            FilterTypes.CHEBYSHEV_TYPE_1.value,
+            RIPPLE,
+        )
+
+        assert np.all(np.isfinite(filtered)), '%s produced non-finite samples' % name
+        # The tone the filter is meant to keep survives close to full amplitude.
+        assert amplitude_at(filtered, kept) > 0.8, (name, amplitude_at(filtered, kept))
+        # The tone it is meant to reject is pushed far down.
+        assert amplitude_at(filtered, removed) < 0.05, (name, amplitude_at(filtered, removed))
+
+    print('chebyshev band filter regression passed')
+
+
+if __name__ == '__main__':
+    main()

src/data_handler/data_handler.cpp

@@ -294,14 +294,17 @@ int perform_bandpass (double *data, int data_len, int sampling_rate, double star
     }
 
     Dsp::Params params;
+    params.clear ();
     params[0] = sampling_rate; // sample rate
     params[1] = order;         // order
     params[2] = center_freq;   // center freq
-    params[3] = band_width;
+    params[3] = band_width;    // band width
     if ((filter_type == (int)FilterTypes::CHEBYSHEV_TYPE_1) ||
         (filter_type == (int)FilterTypes::CHEBYSHEV_TYPE_1_ZERO_PHASE))
     {
-        params[3] = ripple; // ripple
+        // band pass and band stop chebyshev designs take 5 params and expect the ripple after
+        // the band width, unlike the low pass and high pass designs which take 4
+        params[4] = ripple; // ripple
     }
     f->setParams (params);
     f->process (data_len, filter_data);
@@ -362,14 +365,17 @@ int perform_bandstop (double *data, int data_len, int sampling_rate, double star
     }
 
     Dsp::Params params;
+    params.clear ();
     params[0] = sampling_rate; // sample rate
     params[1] = order;         // order
     params[2] = center_freq;   // center freq
-    params[3] = band_width;
+    params[3] = band_width;    // band width
     if ((filter_type == (int)FilterTypes::CHEBYSHEV_TYPE_1) ||
         (filter_type == (int)FilterTypes::CHEBYSHEV_TYPE_1_ZERO_PHASE))
     {
-        params[3] = ripple; // ripple
+        // band pass and band stop chebyshev designs take 5 params and expect the ripple after
+        // the band width, unlike the low pass and high pass designs which take 4
+        params[4] = ripple; // ripple
     }
     f->setParams (params);
     f->process (data_len, filter_data);