##############################################################################
#
# Morse sound file generator
#
# Generate a .wav file playing user text in Morse code
#
# Copyright (C) 2012-2025 Christophe DAVID ( ON6ZQ | AC6ZQ )
#
##############################################################################

clear;
clc;
close all;

# User-configurable parameters
text = "73 de ON6ZQ";
WordsPerMinute = 20;
OutputDirectory = '';
ToneFrequency = 600;       # in Hertz
SamplingRate = 22500;      # samples per second
BitDepth = 16;             # 8, 16, 24, 32 bits
EnvelopeSmoothingMethod = 2; # 0: none, 1: cosine, 2: Gaussian
RiseTime = 0.010;          # seconds
FallTime = 0.010;          # seconds

##############################################################################
# Convert input text to Morse code
function OutputMatrix = TextToMorse(InputString)
    morse = cell(1, 128);

    morse{48+1} = '-----'; morse{49+1} = '.----'; morse{50+1} = '..---';
    morse{51+1} = '...--'; morse{52+1} = '....-'; morse{53+1} = '.....';
    morse{54+1} = '-....'; morse{55+1} = '--...'; morse{56+1} = '---..';
    morse{57+1} = '----.';

    letters = {
        '.-', '-...', '-.-.', '-..', '.', '..-.', '--.', '....', '..', '.---', ...
        '-.-', '.-..', '--', '-.', '---', '.--.', '--.-', '.-.', '...', '-', ...
        '..-', '...-', '.--', '-..-', '-.--', '--..'
    };

    for k = 65:90
        morse{k+1} = letters{k-64};
        morse{k+33} = letters{k-64};  # lower-case
    end

    InputString = char(InputString);
    OutputMatrix = cellstr("");
    M = double(InputString);

    for i = 1:length(M)
        if M(i) <= length(morse) && ~isempty(morse{M(i)+1})
            OutputMatrix{i} = morse{M(i)+1};
        else
            OutputMatrix{i} = "";
        end
    end
endfunction

##############################################################################
# Gaussian envelope function
function f = GaussDistribution(x, mu, s)
    f = exp(-0.5 * ((x - mu) ./ s).^2) ./ (s * sqrt(2*pi));
endfunction

##############################################################################
# Morse timing units
UnitsPerDit = 1;
UnitsPerDah = 3;
UnitsBetweenElements = 1;
UnitsBetweenCharacters = 3;
UnitsBetweenWords = 7;
UnitDuration = 1.2 / WordsPerMinute;

InterElements = zeros(1, round(UnitsBetweenElements * UnitDuration * SamplingRate));
InterCharacters = zeros(1, round(UnitsBetweenCharacters * UnitDuration * SamplingRate));
InterWords = zeros(1, round(UnitsBetweenWords * UnitDuration * SamplingRate));

Dit = 0:1:(UnitsPerDit * UnitDuration * SamplingRate);
Dah = 0:1:(UnitsPerDah * UnitDuration * SamplingRate);
Dit = sin((Dit / SamplingRate) * 2 * pi * ToneFrequency);
Dah = sin((Dah / SamplingRate) * 2 * pi * ToneFrequency);

# Apply envelope smoothing
if EnvelopeSmoothingMethod > 0
    SmoothRise = 1:(RiseTime * SamplingRate);
    SmoothFall = (FallTime * SamplingRate):-1:1;

    switch EnvelopeSmoothingMethod
        case 1  # Cosine
            SmoothRise = sin((SmoothRise / SamplingRate) * (pi/(2 * RiseTime)));
            SmoothFall = sin((SmoothFall / SamplingRate) * (pi/(2 * FallTime)));
        case 2  # Gaussian
            mu = RiseTime * SamplingRate;
            s = mu / 2;
            SmoothRise = GaussDistribution(SmoothRise, mu, s);
            SmoothFall = GaussDistribution(SmoothFall, mu, s);
            SmoothRise = SmoothRise / max(SmoothRise);
            SmoothFall = SmoothFall / max(SmoothFall);
        otherwise
            error("Unsupported smoothing method.");
    end

    figure; plot(SmoothRise, 'g'); hold on; plot(SmoothFall, 'r'); legend("SmoothRise", "SmoothFall");
    FileName = sprintf("%sMorseSoundFileGenerator_Envelope_%da.jpg", OutputDirectory, EnvelopeSmoothingMethod);
    print(FileName, "-djpg");

    printf("Envelope smoothing plot saved to %s\n", FileName);
    input("Press Enter to continue...\n", "s");
    clf;

    Dit(1:length(SmoothRise)) = Dit(1:length(SmoothRise)) .* SmoothRise;
    Dah(1:length(SmoothRise)) = Dah(1:length(SmoothRise)) .* SmoothRise;

    Dit(end-length(SmoothFall)+1:end) = Dit(end-length(SmoothFall)+1:end) .* SmoothFall;
    Dah(end-length(SmoothFall)+1:end) = Dah(end-length(SmoothFall)+1:end) .* SmoothFall;
end

figure; plot(Dit);
FileName = sprintf("%sMorseSoundFileGenerator_Dit_%db.jpg", OutputDirectory, EnvelopeSmoothingMethod);
print(FileName, "-djpg");

printf("Modified 'Dit' waveform plot saved to %s\n", FileName);
input("Press Enter to continue...\n", "s");
clf;

##############################################################################
# Generate the Morse signal
MorseText = TextToMorse(text);
SoundData = [];

for i = 1:length(MorseText)
    symbol = MorseText{i};
    if isempty(symbol)
        SoundData = [SoundData, InterWords];
    else
        for j = 1:length(symbol)
            switch symbol(j)
                case '-'
                    SoundData = [SoundData, Dah];
                case '.'
                    SoundData = [SoundData, Dit];
                otherwise
                    printf("Cannot send: %s\n", symbol(j));
            end
            SoundData = [SoundData, InterElements];
        end
        SoundData = [SoundData, InterCharacters];
    end
end

##############################################################################
# Save to WAV file
FileName = sprintf("%sMorseSoundFileGenerator_%d.wav", OutputDirectory, EnvelopeSmoothingMethod);
audiowrite(FileName, SoundData', SamplingRate, 'BitsPerSample', BitDepth);

printf("\nMorse code audio saved to: %s\n", FileName);