fix(vhs-decode): avoid negative values in linear_filter, use a bit le…

…ss padding in filter_simple, only pass real to filter_simple

vhsdecode/nonlinear_filter.py

@@ -72,14 +72,14 @@ def sub_deemphasis_inner(
     # Get the instantaneous amplitude of the signal using the hilbert transform
     # and divide by the formats specified deviation so we get a amplitude compared to the specifications references.
     amplitude = abs(sps.hilbert(hf_part)) / deviation
-    amplitude = filter_simple(amplitude, filters["NLAmplitudeLPF"])
-
+    # Clip the value after filtering to make sure we don't go negative
+    amplitude = np.clip(filter_simple(amplitude, filters["NLAmplitudeLPF"]), 0, None)
     if debug_const_amplitude:
         amplitude = debug_const_amplitude
 
     if linear_scale_1 is not None:
         amplitude *= linear_scale_1
-    # Scale the amplitude by a exponential factore (typically less than 1 so it ends up being a root function of osrts)
+    # Scale the amplitude by a exponential factore (typically less than 1 so it ends up being a root function of sorts)
     amplitude = np.power(amplitude, exponential_scale)
     if linear_scale_2 is not None:
         amplitude *= linear_scale_2

vhsdecode/process.py

@@ -1121,7 +1121,7 @@ def demodblock(
         # on sharp transitions. Using filtfilt to avoid phase issues.
         if len(np.where(env == 0)[0]) == 0:  # checks for zeroes on env
             if self._high_boost is not None:
-                data_filtered = npfft.ifft(indata_fft)
+                data_filtered = npfft.ifft(indata_fft).real
                 high_part = utils.filter_simple(
                     data_filtered, self.Filters["RFTop"]
                 ) * ((env_mean * 0.9) / env)

vhsdecode/utils.py

@@ -18,7 +18,7 @@ def gen_compl_wave_at_frequency(frequency, sample_frequency, num_samples):
 
 
 def filter_simple(data, filter_coeffs):
-    return signal.sosfiltfilt(filter_coeffs, data, padlen=150)
+    return signal.sosfiltfilt(filter_coeffs, data, padlen=70)
 
 
 @njit(cache=True)