Oscillator

Eric Ludlam
/
Oscillator
on 9 Oct 2024
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function drawframe(f)
samplerate = 12000;
    
    persistent osc p
    if f==1
        osc = oscillator();
        % Axes to draw into
        p = plot(1:10,'linewidth',2);
        title('Oscillator Signal');
        ylabel('Signal Strength');
        ylim([-32767 32767]);
        xlim tight
    end
    % Basic time changes for frequency, volume, & vibratto freq & depth
    F=cospi(f/48)+1;
    V=sinpi(f/48)/3+.65;
    VF=sinpi(f/24)+1;
    VD=cospi(f/24)+1;
    if f==96
        % Avoid a pop when this repeats.
        V=0;
    end
    
    % Adjust simple number into ranges for those values
    sample = osc.frame(V,F*100+10,VF*10+5,VD*100+50);
    % Plot it
    set(p,'xdata',1:size(sample,1),'ydata',sample);
    %% Audio Playback
    % For testing in desktop MATLAB.  You'll need DSP toolbox.
    %persistent player
    %if f==1
    %    player = audioDeviceWriter('SampleRate',samplerate);
    %end
    %player(sample);
    %if f==96
    %    delete(player)
    %end
    %% Saving the audio
    % For building the MP3 during testing
    %persistent audiotrack
    %if f==1
    %    audiotrack = int16([]);
    %end
    %audiotrack = [ audiotrack
    %               sample ];
    %if f==96
    %    audiowrite('oscillator_tmp.mp3', audiotrack, samplerate);
    %end
    function osc = oscillator()
    % Create a mini stateful oscillator object.
        
        last_freq=0;
        last_vol=0;
        last_space_value=0;
        % Vibratto Freq & Volume
        last_vib_freq=0;
        last_vib_depth=0;
        last_vib_space_value=0;
        osc.frame = @frame;
        function sample = frame(vol,freq,vib_freq,vib_depth)
        % Do one frame computing an oscillating audio signal
        % Based on FPS and SampleRate, returns a sample that will
        % fill one "frame" at that FPS.
        %
        % freq - frequency of signal
        % vol - volume
        % vib_freq - vibratto frequency
        % vib_depth - vibratto depth (how much frequency shift)
            
        % I cobbled this together without being familiar with
        % signal synthisis when I started.  If there is a better
        % way, remix or leave a comment.
            
        % compute length of our sample
            Tlen = samplerate/24; % samplerate/fps;
            % Compute the vibratto pattern.
            if vib_freq > 0 && vib_depth > 0
                vramp = linspace(last_vib_freq, vib_freq, Tlen)';
                venvelope = linspace(last_vib_depth, vib_depth, Tlen)';
                % Just the adjusted wave to be added to ramp
                vib_space = cumsum(vramp/samplerate*2)+last_vib_space_value;
                vib_wave = sinpi(vib_space*2) .* venvelope;
                last_vib_space_value = mod(vib_space(end),2);
                last_vib_freq = vib_freq;
                last_vib_depth = vib_depth;
            else
                vib_wave = 0;
            end
            % Compute a frequency ramp which is flat if last and current
            % are the same.
            ramp = linspace(last_freq, freq, Tlen)';
            % based on sample rate, create the repeating pattern.
            space = cumsum((ramp+vib_wave)/samplerate*2)+last_space_value;
            % Remember last value so our next sample fits in nicely.
            last_space_value = mod(space(end),2);
            % Remember last frequency we used so we can ramp toward any new value.
            last_freq = freq;
            % Generate the wave form.
            %switch wave
            %  case 'sin'
            Wave = sinpi(space*2);
            %  case 'saw'
            %    Wave = -(mod(space,2)-1);
            %  case 'square'
            %    Wave = floor(mod(space,2))*2-1;
            %end
            % Compute the volume envelope to smoothly transition
            % from old to new volume, and then apply.
            vol_envelope = linspace(last_vol,vol,Tlen)';
            doublesample = vol_envelope.*Wave;
            last_vol = vol;
            % Convert to int16.
            int16vol = 32767;
            sample = int16(doublesample*int16vol);
        end
    end
end
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