Plot signal channels

def plot_signal(signal, sig_len, n_sig, fs, time_units, sig_style, axes):
    "Plot signal channels"

    # Extend signal style if necesary
    if len(sig_style) == 1:
        sig_style = n_sig * sig_style

    # Figure out time indices
    if time_units == 'samples':
        t = np.linspace(0, sig_len-1, sig_len)
    else:
        downsample_factor = {'seconds':fs, 'minutes':fs * 60,
                             'hours':fs * 3600}
        t = np.linspace(0, sig_len-1, sig_len) / downsample_factor[time_units]

    # Plot the signals
    if signal.ndim == 1:
        axes[0].plot(t, signal, sig_style[0], zorder=3)
    else:
        for ch in range(n_sig):
            axes[ch].plot(t, signal[:,ch], sig_style[ch], zorder=3)