Global Name non definito

from math import *

def sinwave(N, fc, freq): # genera funzione seno
    result = []
    for x in range(N):
        result.append(32000*cos(2*pi*freq*x/fc-pi/2))
    return result

def squarewave(N,fc,freq,dc): # genera funzione quadra
    result = []
    for x in range(N):
        if x<N/2 :
            result.append(32000)
        if x>=N/2:
            result.append(0)
    return result