function [time, sine] = sinewave(freq, ampl, duration, step)
% compute sine wave with time axis
% freq: frequency of the sinewave in Hertz
% ampl: amplitude of the sinewave
% duration: duration of the sinewave in seconds
% step: stepsize for plotting in seconds
% returns:
% time: vector of time points
% sine: corresponding vector with the sine wave
time = 0:step:duration;
sine = ampl*sin(2*pi*freq*time);
end