Fs = 8000
dtmf = sio.loadmat('dtmf1.mat')
dictlist = []

for key, value in dtmf.items():
    temp = [key,value]
    dictlist.append(temp)

f1, t1, Zxx1 = signal.stft(dictlist, Fs, nperseg=512,
                           window=signal.hamming(512),
                           noverlap=512, boundary='even')

plt.figure()
plt.pcolormesh(t1, f1, 20*np.log10(np.abs(Zxx1)))
plt.xlabel('Time [s]')
plt.ylabel('Freq [Hz]')$