Question

I’m trying to export the data that is shown in plot(yi) using wavwrite. When I do an interpolation the (yi) signal doesn’t start at zero how can I get (yi) the interpolated signal to start at zero? Please note that I can’t just do a plot(xxorig, yi) due to the fact that wavwrite doesn’t work this way. Does anyone know a work around?

I’m using octave 3.2.4/matlab

clear all, clf
xxorig=[0, 0.418879, 0.837758, 1.25664, 1.67552, 2.0944, 2.51327, 2.93215, 3.35103, 3.76991, 4.18879, 4.60767, 5.02655, 5.44543, 5.86431, 6.28319];
xx=[0, 0.296192, 0.592384, 0.888577, 1.18477, 1.48096, 1.77715, 2.07335, 2.36954, 2.66573, 2.96192, 3.25811, 3.55431, 3.8505, 4.14669, 4.44288];
yy=[0, 0.406737, 0.743145, 0.951057, 0.994522, 0.866025, 0.587785, 0.207912, -0.207912, -0.587785, -0.866025, -0.994522, -0.951057, -0.743145, -0.406737, -2.44929e-16];

yi=interp1(xx,yy,xxorig);
subplot(4,1,1),plot(xxorig,yy),title("plot(xxorig,yy)")
subplot(4,1,2),plot(xx,yy),title("plot(xx,yy)")
subplot(4,1,3),plot(yy),title("plot(yy)")
subplot(4,1,4),plot(yi),title("plot(yi)")
wavwrite([yy'] ,16,32,'/tmp/test.wav')

Answer 1

It’s unclear what are you trying to export – plot or sound wav file of the signal?

You use WAVWRITE to save the sound in WAVE format. In this case you pass signal intensity yi and optionally a sample rate (the default rate is 8000 Hz). You souldn’t care that your signal does not start at 0.

I believe you can calculate your sample rate for yi as

Fs = numel(xxorig)/(xxorig(end)-xxorig(1));

If you want to PLOT the signal you specify the time on X axis. If you don’t pass x to the plot function it uses just order numbers starting from 1. This is why your plot(yi) or plot(yy) curve does not start at 0.