hello Joshua
this is my suggestion / code below.
It shows how to update the contents of a plot without (re)creating the entire plot structure at each time iteration (which can be pretty slow for complex figures)
so the plot is created only once and then we update some data and axes properties / values
I tested my code also on dummy sine waves just to make sure the correct data is displayed in the correct subplot.
a few things I added :
- apply a window to data before doing the fft (as the buffer of data does not start neither ends with zero)
- optional : use a exponential averaging of the fft data (a factor)
hope it helps
clc
load('ch1_first_5s.mat');
load('ch2_first_5s.mat');
fs = 128;
n1 = 0:1:((5 * fs) - 1);
n2 = 1:1:(fs - 1);
%%% FFT exponential averaging coefficient
a = 0 ; % a = 0 : no averaging; a = 0.9 : highly averaged ; do not exceed 0.99 !!
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% % my test data % debug only
% dt = 1/fs;
% time = n1*dt;
% ch1_first_5s = 10*sin(2*pi*10*time);
% ch2_first_5s = 20*sin(2*pi*20*time);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% data initialisation %
ci = 1;
x_buffer = (ci + n2);
ch1_buffer = ch1_first_5s(ci + n2);
ch2_buffer = ch2_first_5s(ci + n2);
ch_buffer = [ch1_buffer;ch2_buffer];
%% plot
h = figure(1),
subplot(2, 2, 1);
plot(x_buffer, ch_buffer(1,:), 'b');
title('Channel 1 - Time Domain EEG plot');
ylim([-200 200]); ylabel('Amplitude');
xlim([ci (ci + 128)]); xlabel('Discrete Time n (Sample Number)');
grid on;
subplot(2, 2, 3);
plot(x_buffer, ch_buffer(2,:), 'b');
title('Channel 2 - Time Domain EEG plot');
ylim([-200 200]); ylabel('Amplitude');
xlim([ci (ci + 128)]); xlabel('Discrete Time n (Sample Number)');
grid on;
N = length(n2)+1;
N1 = (2)^nextpow2(N);
window = hanning(length(n2));
X_k1 = fft(ch1_buffer.*window', N1); X_k1 = X_k1(1:(N1 / 2));
X_k2 = fft(ch2_buffer.*window', N1); X_k2 = X_k2(1:(N1 / 2));
Mag1_dB = 20*log10(abs(X_k1)*4/N1);
Mag2_dB = 20*log10(abs(X_k2)*4/N1);
Mag1_dB_old = Mag1_dB;
Mag2_dB_old = Mag2_dB;
freq = fs * (0:(N1 / 2) - 1) / N1;
subplot(2, 2, 2);
plot(freq, Mag1_dB, 'b');
ylim([-60 40]); ylabel('Magnitude (dB)');
xlim([0 freq(end)]); xlabel('Frequency (Hz)');
title('Channel 1 - Freq Domain EEG plot');
grid on;
subplot(2, 2, 4);
plot(freq, Mag2_dB, 'b');
ylim([-60 40]); ylabel('Magnitude (dB)');
xlim([0 freq(end)]); xlabel('Frequency (Hz)');
title('Channel 2 - Freq Domain EEG plot');
grid on;
%%------The axis handle code-----------------------
h=findobj(gcf,'type','axes');
% h = 4×1 Axes array:
% Axes (Channel 2 - Freq Domain EEG plot)
% Axes (Channel 1 - Freq Domain EEG plot)
% Axes (Channel 2 - Time Domain EEG plot)
% Axes (Channel 1 - Time Domain EEG plot)
% please not that the axes array do not reflect the subplot order !
%% loop to update figure / axes handle
for ci = 1:1:511
% update for LHS time plots
x_buffer = (ci + n2);
ch1_buffer = ch1_first_5s(ci + n2);
ch2_buffer = ch2_first_5s(ci + n2);
ch_buffer = [ch2_buffer;ch1_buffer]; % reversed order because so are the axes handle
% update for RHS FFT plots
X_k1 = fft(ch1_buffer.*window', N1); X_k1 = X_k1(1:(N1 / 2));
X_k2 = fft(ch2_buffer.*window', N1); X_k2 = X_k2(1:(N1 / 2));
Mag1_dB = a*Mag1_dB_old+(1-a)*20*log10(abs(X_k1)*4/N1); % exponential averaging
Mag2_dB = a*Mag2_dB_old+(1-a)*20*log10(abs(X_k2)*4/N1); % exponential averaging
Mag_buffer = [Mag2_dB;Mag1_dB]; % reversed order because so are the axes handle
% update FFT Mag
Mag1_dB_old = Mag1_dB;
Mag2_dB_old = Mag2_dB;
% update handles
for k=1:4
f=get(h(k),'children');
if k == 3 || k == 4
set(f,'xdata',x_buffer);
set(h(k),'XLim',[ci (ci + 128)]);
set(f,'ydata',ch_buffer(k-2,:));
elseif k == 1 || k == 2
set(f,'ydata',Mag_buffer(k,:));
end
end
pause(0.05);
drawnow
end
