Add EQ effect for AudioSegment (#492)

* Issue #316

Added a Equaliser Function

* Update effects.py

* Update scipy_effects.py

Corrected the Exampled

* Added Mid-Side and Reverse Conversion

* Update README.markdown

* Update README.markdown

* Update utils.py

* Update utils.py

Breathe in Bug out

* Update Documentation for eq()

* New eq function

Updated eq function with channel independent mode and some error handling. Not Tested Thoroughly.

* Cleaning

* Cleaned

* Update scipy_effects.py

* Update utils.py

* Cleaning

MS Filter Bug Removed

Co-authored-by: James Robert <github@jiaaro.com>

pydub/scipy_effects.py

@@ -10,7 +10,7 @@
 provided by pydub.effects.
 """
 from scipy.signal import butter, sosfilt
-from .utils import register_pydub_effect
+from .utils import (register_pydub_effect,stereo_to_ms,ms_to_stereo)
 
 
 def _mk_butter_filter(freq, type, order):
@@ -62,3 +62,114 @@ def high_pass_filter(seg, cutoff_freq, order=5):
 def low_pass_filter(seg, cutoff_freq, order=5):
     filter_fn = _mk_butter_filter(cutoff_freq, 'lowpass', order=order)
     return seg.apply_mono_filter_to_each_channel(filter_fn)
+
+
+@register_pydub_effect
+def _eq(seg, focus_freq, bandwidth=100, mode="peak", gain_dB=0, order=2):
+    """
+    Args:
+        focus_freq - middle frequency or known frequency of band (in Hz)
+        bandwidth - range of the equalizer band
+        mode - Mode of Equalization(Peak/Notch(Bell Curve),High Shelf, Low Shelf)
+        order - Rolloff factor(1 - 6dB/Octave 2 - 12dB/Octave)
+    
+    Returns:
+        Equalized/Filtered AudioSegment
+    """
+	filt_mode = ["peak", "low_shelf", "high_shelf"]
+	if mode not in filt_mode:
+		raise ValueError("Incorrect Mode Selection")
+
+	if gain_dB >= 0:
+		if mode == "peak":
+			sec = band_pass_filter(seg, focus_freq - bandwidth/2, focus_freq + bandwidth/2, order = order)
+			seg = seg.overlay(sec - (3 - gain_dB))
+			return seg
+
+		if mode == "low_shelf":
+			sec = low_pass_filter(seg, focus_freq, order=order)
+			seg = seg.overlay(sec - (3 - gain_dB))
+			return seg
+
+		if mode == "high_shelf":
+			sec = high_pass_filter(seg, focus_freq, order=order)
+			seg = seg.overlay(sec - (3 - gain_dB))
+			return seg
+
+	if gain_dB < 0:
+		if mode == "peak":
+			sec = high_pass_filter(seg, focus_freq - bandwidth/2, order=order)
+			seg = seg.overlay(sec - (3 + gain_dB)) + gain_dB
+			sec = low_pass_filter(seg, focus_freq + bandwidth/2, order=order)
+			seg = seg.overlay(sec - (3 + gain_dB)) + gain_dB
+			return seg
+
+		if mode == "low_shelf":
+			sec = high_pass_filter(seg, focus_freq, order=order)
+			seg = seg.overlay(sec - (3 + gain_dB)) + gain_dB
+			return seg
+
+		if mode=="high_shelf":
+			sec=low_pass_filter(seg, focus_freq, order=order)
+			seg=seg.overlay(sec - (3 + gain_dB)) +gain_dB
+			return seg
+
+
+@register_pydub_effect
+def eq(seg, focus_freq, bandwidth=100, channel_mode="L+R", filter_mode="peak", gain_dB=0, order=2):
+	"""
+	Args:
+		focus_freq - middle frequency or known frequency of band (in Hz)
+		bandwidth - range of the equalizer band
+		channel_mode - Select Channels to be affected by the filter.
+			L+R - Standard Stereo Filter
+			L - Only Left Channel is Filtered
+			R - Only Right Channel is Filtered
+			M+S - Blumlien Stereo Filter(Mid-Side)
+			M - Only Mid Channel is Filtered
+			S - Only Side Channel is Filtered
+			Mono Audio Segments are completely filtered.
+		filter_mode - Mode of Equalization(Peak/Notch(Bell Curve),High Shelf, Low Shelf)
+		order - Rolloff factor(1 - 6dB/Octave 2 - 12dB/Octave)
+	
+	Returns:
+		Equalized/Filtered AudioSegment
+    """
+	filt_mode = ["L+R", "M+S", "L", "R", "M", "S"]
+	if mode not in filt_mode:
+		raise ValueError("Incorrect Channel Mode Selection")
+
+	if seg.channels == 1:
+		return _eq(seg, focus_freq, bandwidth, filter_mode, gain_dB, order)
+
+	if channel_mode == "L+R":
+		return _eq(seg, focus_freq, bandwidth, filter_mode, gain_dB, order)
+
+	if channel_mode == "L":
+		seg = seg.split_to_mono()
+		seg = [_eq(seg[0], focus_freq, bandwidth, filter_mode, gain_dB, order), seg[1]]
+		return AudioSegment.from_mono_audio_segements(seg[0], seg[1])
+
+	if channel_mode == "R":
+		seg = seg.split_to_mono()
+		seg = [seg[0], _eq(seg[1], focus_freq, bandwidth, filter_mode, gain_dB, order)]
+		return AudioSegment.from_mono_audio_segements(seg[0], seg[1])
+
+	if channel_mode == "M+S":
+		seg = stereo_to_ms(seg)
+		seg = _eq(seg, focus_freq, bandwidth, filter_mode, gain_dB, order)
+		return ms_to_stereo(seg)
+
+	if channel_mode == "M":
+		seg = stereo_to_ms(seg).split_to_mono()
+		seg = [_eq(seg[0], focus_freq, bandwidth, filter_mode, gain_dB, order), seg[1]]
+		seg = AudioSegment.from_mono_audio_segements(seg[0], seg[1])
+		return ms_to_stereo(seg)
+
+	if channel_mode == "S":
+		seg = stereo_to_ms(seg).split_to_mono()
+		seg = [seg[0], _eq(seg[1], focus_freq, bandwidth, filter_mode, gain_dB, order)]
+		seg = AudioSegment.from_mono_audio_segements(seg[0], seg[1])
+		return ms_to_stereo(seg)
+
+

pydub/utils.py

@@ -415,3 +415,20 @@ def get_supported_decoders():
 
 def get_supported_encoders():
     return get_supported_codecs()[1]
+
+def stereo_to_ms(audio_segment):
+	'''
+	Left-Right -> Mid-Side
+	'''
+	channel = audio_segment.split_to_mono()
+	channel = [channel[0].overlay(channel[1]), channel[0].overlay(channel[1].invert_phase())]
+	return AudioSegment.from_mono_audiosegments(channel[0], channel[1])
+
+def ms_to_stereo(audio_segment):
+	'''
+	Mid-Side -> Left-Right
+	'''
+	channel = audio_segment.split_to_mono()
+	channel = [channel[0].overlay(channel[1]) - 3, channel[0].overlay(channel[1].invert_phase()) - 3]
+	return AudioSegment.from_mono_audiosegments(channel[0], channel[1])
+