Add a convenience method for producing a FrequencyBand instance repre…

…senting the audible frequency range of a given audio sample rate

zounds/__init__.py

@@ -18,7 +18,7 @@
     SpectralFlatness, AWeighting, LinearScale, FrequencyBand, \
     FrequencyScale, FrequencyDimension, GeometricScale, HanningWindowingFunc, \
     FrequencyAdaptiveTransform, ExplicitScale, ExplicitFrequencyDimension, \
-    FrequencyAdaptive, FrequencyWeighting, Hertz, BarkScale, MelScale, \
+    FrequencyAdaptive, FrequencyWeighting, Hertz, Hz, BarkScale, MelScale, \
     ChromaScale, fir_filter_bank
 
 from loudness import \

zounds/spectral/__init__.py

@@ -17,7 +17,7 @@
 
 from frequencyscale import \
     LinearScale, FrequencyBand, FrequencyScale, GeometricScale, ExplicitScale, \
-    Hertz, BarkScale, MelScale, ChromaScale
+    Hertz, Hz, BarkScale, MelScale, ChromaScale
 
 from frequencyadaptive import FrequencyAdaptive
 

zounds/spectral/frequencyscale.py

@@ -12,11 +12,14 @@ def __neg__(self):
         return Hertz(-self.hz)
 
     def __add__(self, other):
-        return Hertz(self + other)
+        return Hertz(self.hz + other.hz)
+
+
+class Hz(Hertz):
+    pass
 
 
 # TODO: What commonalities can be factored out of this class and TimeSlice?
-# TODO: Deprecate stuff in psychoacoustics.py in favor of these classes
 class FrequencyBand(object):
     """
     Represents an interval, or band of frequencies in hertz (cycles per second)
@@ -71,6 +74,10 @@ def intersect(self, other):
         highest_start = max(self.start_hz, other.start_hz)
         return FrequencyBand(highest_start, lowest_stop)
 
+    @classmethod
+    def audible_range(cls, samplerate):
+        return FrequencyBand(Hz(20), Hz(samplerate.nyquist))
+
     def bandwidth_ratio(self, other):
         return other.bandwidth / self.bandwidth
 

zounds/spectral/test_frequencyscale.py

@@ -1,7 +1,7 @@
 from __future__ import division
 import unittest2
 from frequencyscale import \
-    FrequencyBand, LinearScale, ExplicitScale, GeometricScale, Hertz
+    FrequencyBand, LinearScale, ExplicitScale, GeometricScale, Hertz, Hz
 from zounds.timeseries import SR44100
 import numpy as np
 
@@ -11,6 +11,14 @@ def test_can_negate_hertz(self):
         hz = -Hertz(10)
         self.assertIsInstance(hz, Hertz)
 
+    def test_can_add_hertz(self):
+        hz = Hertz(20) + Hertz(30)
+        self.assertEqual(Hertz(50), hz)
+
+    def test_can_subtract_hertz(self):
+        hz = Hz(100) - Hz(20)
+        self.assertEqual(Hz(80), hz)
+
 
 class FrequencyBandTests(unittest2.TestCase):
     def test_can_create_from_center_frequency(self):
@@ -46,6 +54,15 @@ def test_intersection_ratio(self):
         ratio = fb1.intersection_ratio(fb2)
         self.assertEqual(0.5, ratio)
 
+    def test_audible_range_lower_bound(self):
+        band = FrequencyBand.audible_range(SR44100())
+        self.assertEqual(20, band.start_hz)
+
+    def test_audible_range_upper_bound(self):
+        sr = SR44100()
+        band = FrequencyBand.audible_range(sr)
+        self.assertEqual(int(sr) // 2, band.stop_hz)
+
 
 class FrequencyScaleTests(unittest2.TestCase):
     def test_get_slice_converts_frequency_band_to_integer_based_slice(self):