remove deemph.plt

app/src/main/cpp/sox/deemph.plt

@@ -1,118 +0,0 @@
-# 15/50us EIAJ de-emphasis filter for CD/DAT
-#
-# 09/02/98 (c) Heiko Eissfeldt
-#
-# 18/03/07 robs@users.sourceforge.net: changed to biquad for slightly
-# better accuracy.
-#
-# License: LGPL (Lesser Gnu Public License)
-#
-# This implements the inverse filter of the optional pre-emphasis stage
-# as defined by IEC 60908 (describing the audio cd format).
-#
-# Background: In the early days of audio cds, there were recording
-# problems with noise (for example in classical recordings). The high
-# dynamics of audio cds exposed these recording errors a lot.
-#
-# The commonly used solution at that time was to 'pre-emphasize' the
-# trebles to have a better signal-noise-ratio. That is trebles were
-# amplified before recording, so that they would give a stronger signal
-# compared to the underlying (tape) noise.
-#
-# For that purpose the audio signal was prefiltered with the following
-# frequency response (simple first order filter):
-#
-# V (in dB)
-# ^
-# |
-# |~10dB                    _________________
-# |                        /
-# |                       / |
-# |      20dB / decade ->/  |
-# |                     /   |
-# |____________________/_ _ |_ _ _ _ _ _ _ _ _ Frequency
-# |0 dB                |    |
-# |                    |    |
-# |                    |    |
-#                 3.1kHz    ~10kHz
-#
-# So the recorded audio signal has amplified trebles compared to the
-# original.  HiFi cd players do correct this by applying an inverse
-# filter automatically, the cd-rom drives or cd burners used by digital
-# sampling programs (like cdda2wav) however do not.
-#
-# So, this is what this effect does.
-#
-# This is the gnuplot file for the frequency response of the deemphasis.
-#
-# The absolute error is <=0.04dB up to ~12kHz, and <=0.06dB up to 20kHz.
-
-# First define the ideal filter:
-
-# Filter parameters
-T = 1. / 441000.          # we use the tenfold sampling frequency
-OmegaU = 1. / 15e-6
-OmegaL = 15. / 50. * OmegaU
-
-# Calculate filter coefficients
-V0 = OmegaL / OmegaU
-H0 = V0 - 1.
-B = V0 * tan(OmegaU * T / 2.)
-A1 = (B - 1.) / (B + 1.)
-B0 = (1. + (1. - A1) * H0 / 2.)
-B1 = (A1 + (A1 - 1.) * H0 / 2.)
-
-# helper variables
-D = B1 / B0
-O = 2 * pi * T
-
-# Ideal transfer function
-Hi(f) = B0*sqrt((1 + 2*cos(f*O)*D + D*D)/(1 + 2*cos(f*O)*A1 + A1*A1))
-
-# Now use a biquad (RBJ high shelf) with sampling frequency of 44100Hz
-# to approximate the ideal curve:
-
-# Filter parameters
-t = 1. / 44100.
-gain = -9.477
-slope = .4845
-f0 = 5283
-
-# Calculate filter coefficients
-A = exp(gain / 40. * log(10.))
-w0 = 2. * pi * f0 * t
-alpha = sin(w0) / 2. * sqrt((A + 1. / A) * (1. / slope - 1.) + 2.)
-b0 = A * ((A + 1.) + (A - 1.) * cos(w0) + 2. * sqrt(A) * alpha)
-b1 = -2. * A * ((A - 1.) + (A + 1.) * cos(w0))
-b2 = A * ((A + 1.) + (A - 1.) * cos(w0) - 2. * sqrt(A) * alpha)
-a0 = (A + 1.) - (A - 1.) * cos(w0) + 2. * sqrt(A) * alpha
-a1 = 2. * ((A - 1.) - (A + 1.) * cos(w0))
-a2 = (A + 1.) - (A - 1.) * cos(w0) - 2. * sqrt(A) * alpha
-b2 = b2 / a0
-b1 = b1 / a0
-b0 = b0 / a0
-a2 = a2 / a0
-a1 = a1 / a0
-
-# helper variables
-o = 2 * pi * t
-
-# Best fit transfer function
-Hb(f) = sqrt((b0*b0 + b1*b1 + b2*b2 +\
-    2.*(b0*b1 + b1*b2)*cos(f*o) + 2.*(b0*b2)* cos(2.*f*o)) /\
-  (1. + a1*a1 + a2*a2 + 2.*(a1 + a1*a2)*cos(f*o) + 2.*a2*cos(2.*f*o)))
-
-# plot real, best, ideal, level with halved attenuation,
-#   level at full attentuation, 10fold magnified error
-set logscale x
-set grid xtics ytics mxtics mytics
-set key left bottom
-plot [f=1000:20000] [-12:2] \
-20 * log10(Hi(f)),\
-20 * log10(Hb(f)),\
-20 * log10(OmegaL/(2 * pi * f)),\
-.5 * 20 * log10(V0),\
-20 * log10(V0),\
-200 * log10(Hb(f)/Hi(f))
-
-pause -1 "Hit return to continue"