Return channel detect threshold from kal output.

def determine_chan_detect_threshold(kal_out):
    """Return channel detect threshold from kal output."""
    channel_detect_threshold = ""
    while channel_detect_threshold == "":
        for line in kal_out.splitlines():
            if "channel detect threshold: " in line:
                channel_detect_threshold = str(line.split()[-1])
        if channel_detect_threshold == "":
            print("Unable to parse sample rate")
            channel_detect_threshold = None
    return channel_detect_threshold