# -*- coding: utf-8 -*-
from numpy import array, empty, log10
[docs]
def equal_loudness_contours(phones):
""" "This function will return a 29-point equal loudness contour for your desired phon level. The frequencies
evaluated in this function only span from 20Hz - 12.5kHz, and only 29 selective frequencies are covered. This is
the limitation of the ISO standard".
Function based on the MATLAB project from Jeff Tackett, 'ISO 226 Equal-Loudness-Level Contour Signal'
(es.mathworks.com/matlabcentral/fileexchange/7028-iso-226-equal-loudness-level-contour-signal).
Parameters
----------
phones: int
Logarithmic unit for the evaluation curve of the perceived sound (1phon = 1dB @ 1kHz).
Returns
-------
spl_array: numpy.array
Sound pressure level ('SPL') values.
frequencies_array: numpy.array
Frequencies in which the function computes the resulting 'SPL' values.
"""
n_frequencies = 29
freq_array = array([20.0, 25.0, 31.5, 40.0, 50.0, 63.0, 80.0, 100.0, 125.0, 160.0, 200.0, 250.0, 315.0, 400.0,
500.0, 630.0, 800.0, 1000.0, 1250.0, 1600.0, 2000.0, 2500.0, 3150.0, 4000.0, 5000.0, 6300.0,
8000.0, 10000.0, 12500.0])
af = array(
[
0.532,
0.506,
0.480,
0.455,
0.432,
0.409,
0.387,
0.367,
0.349,
0.330,
0.315,
0.301,
0.288,
0.276,
0.267,
0.259,
0.253,
0.250,
0.246,
0.244,
0.243,
0.243,
0.243,
0.242,
0.242,
0.245,
0.254,
0.271,
0.301,
]
)
Lu = array(
[
-31.6,
-27.2,
-23.0,
-19.1,
-15.9,
-13.0,
-10.3,
-8.1,
-6.2,
-4.5,
-3.1,
-2.0,
-1.1,
-0.4,
0.0,
0.3,
0.5,
0.0,
-2.7,
-4.1,
-1.0,
1.7,
2.5,
1.2,
-2.1,
-7.1,
-11.2,
-10.7,
-3.1,
]
)
Tf = array(
[
78.5,
68.7,
59.5,
51.1,
44.0,
37.5,
31.5,
26.5,
22.1,
17.9,
14.4,
11.4,
8.6,
6.2,
4.4,
3.0,
2.2,
2.4,
3.5,
1.7,
-1.3,
-4.2,
-6.0,
-5.4,
-1.5,
6.0,
12.6,
13.9,
12.3,
]
)
# Ln = phones
# Lp = SPL
spl_array = empty(n_frequencies, dtype=float)
# Deriving sound pressure level from loudness level (iso226 sect 4.1). Ln = phones
Af = (4.47 * (10 ** (-3))) * ((10 ** (0.025 * phones)) - 1.15) + (
(0.4 * (10 ** (((Tf + Lu) / 10) - 9))) ** af
)
spl_array = ((10. / af) * log10(Af)) - Lu + 94
return spl_array, freq_array
