From b27aef78a995fd130f90c69827b5661a0d2168d3 Mon Sep 17 00:00:00 2001 From: Neelay Joglekar Date: Fri, 10 Dec 2021 16:57:21 -0800 Subject: [PATCH] Added documentation --- src/LFO/lfo_freq_sine.m | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/src/LFO/lfo_freq_sine.m b/src/LFO/lfo_freq_sine.m index 3fc4273..bef74a5 100644 --- a/src/LFO/lfo_freq_sine.m +++ b/src/LFO/lfo_freq_sine.m @@ -5,11 +5,13 @@ function output = lfo_freq_sine(amplitude, frequency, phase, fs, duration, input % Neelay Joglekar: Original author % SOURCES: -% Code based off of Benjamin Liou's functions (lfo_sine) -% https://dsp.stackexchange.com/questions/2349/help-with-algorithm-for-modulating-oscillator-pitch-using-lfo +% Code inspired by Benjamin Liou's lfo functions +% Code also inspired by Darren and Anne's pitch envelopes +% Source for frequency modulation equation: +% https://dsp.stackexchange.com/questions/2349/help-with-algorithm-for-modulating-oscillator-pitch-using-lfo % DOCUMENTATION: -% Frequency is modulated by 20 semitones (20 above, 20 below) +% Frequency is modulated by sine wave with given amplitude (in octaves, not Hz) % initialize local variables from input arguments n = fs * duration; % number of samples (length of matrix) @@ -18,12 +20,17 @@ function output = lfo_freq_sine(amplitude, frequency, phase, fs, duration, input % create output array output = zeros([1, n]); - x = 0.0; % theoretical input index, assuming input not discrete + x = 0.0; % the theoretical input index if the input were not discrete % populate output for i = 1:n t = i * dt; % time at the i'th sample - omega_ratio = 2 ^ (20/12 * sin(2 * pi * frequency * t - phase)); + + % Increment x based off of sine wave output + omega_ratio = 2 ^ (amplitude * sin(2 * pi * frequency * t - phase)); x = mod(x + omega_ratio, n); + + % Linearly interpolate the actual indicies adjacent to x + % to get an output value x_0 = floor(x) + 1; x_1 = mod(x_0 + 1, n) + 1; output(i) = (input(x_1) - input(x_0)) * (x - x_0) + input(x_0);