import pyfar as pf
sweep = pf.signals.linear_perfect_sweep(2**8)
sweep_shifted = pf.dsp.time_shift(sweep, 2**7)
ax = pf.plot.time_freq(sweep_shifted, unit='samples')
ax[0].axvline(2**7, ls='--', c='r', label='start/end')
ax[0].legend(loc=4)