make a voice sound signal play faster
You can increase the sampling rate, instead of the signal $x(nT_s) = x(n/F_s)$, you can play it at say $\frac{11}{10}F_s, \frac{12}{10}F_s, \text{or}\ 2F_s$. So you have:
\begin{align}
x\left(\frac{n}{\frac{11}{10}F_s}\right) &amp;=x\left(\frac{10n}{11F_s}\right) = x\left(n\frac{10}{11}T_s\right)\\
x\left(\frac{n}{\frac{12}{10}F_s}\right) &amp;=x\left(\frac{10 n}{12F_s}\right) = x\left(n\frac{10}{12}T_s\right)\\
x\left(\frac{n}{2F_s}\right) &amp;=x\left(\frac{1}{2}\frac{n}{F_s}\right) = x\left(n\frac{1}{2}T_s\right) 
\end{align}
In MATLAB for instance, you can try the code below. 

clear all

load handel.mat
sound(y, Fs) % original 
sound(y, 1.1*Fs) % at 1.1*Fs
sound(y, 1.2*Fs) % at 1.2*Fs
sound(y, 2*Fs) % at twice Fs


Gradually increasing the frequency to hear the changes in speed. You can try even higher, like 4 times, to hear the differences. The handel.mat file should be in there by default. 

EDIT:

You $x(t)$ in your program is samples of the signal for a certain time duration, check how many samples you have per second (i.e. the sampling rate or frequency $F_s$), and $T_s = 1/F_s$. And $x(t) = x(nT_s) = x(n/F_s)$ with $n = 0, \ldots, N-1$ where $N$ is the number of samples. Taking a higher $F_s$ corresponds to taking smaller $T_s$.