def clipping_rate(self, factor):
"""
Return the clipping rate of the frames.
@param factor (float) An interval to be more precise on clipping rate.
It will consider that all frames outside the interval are clipped.
Factor has to be between 0 and 1.
@return the clipping rate
"""
if self.sampwidth == 4 :
data = struct.unpack("<%ul" % (len(self.frames) / 4), self.frames)
elif self.sampwidth == 2 :
data = struct.unpack("<%uh" % (len(self.frames) / 2), self.frames)
else :
data = struct.unpack("%uB" % len(self.frames), self.frames)
data = [ s - 128 for s in data ]
maxval = audioutils.get_maxval(self.sampwidth)*(factor/2.)
minval = audioutils.get_minval(self.sampwidth)*(factor/2.)
nbclipping = 0
for i in xrange(len(data)):
if data[i] >= maxval or data[i] <= minval:
nbclipping = nbclipping + 1
return float(nbclipping)/len(data)
def _sampleCalculator(self, channels, pos, sampwidth, factors, attenuator):
"""
Return the sample value, applying a factor and an attenuator.
@param channels (Channel[]) the list of channels
@param pos (int) the position of the sample to calculate
@param sampwidth (int) the sample width
@param factors (float[]) the list of factors to apply to each sample of a channel (1 channel = 1 factor)
@param attenuator (float) a factor to apply to each sum of samples
@return the value of the sample calculated (float)
"""
# variables to compare the value of the result sample to avoid clipping
minval = audioutils.get_minval(sampwidth)
maxval = audioutils.get_maxval(sampwidth)
# the result sample is the sum of each sample with the application of the factors
sampsum = 0
for factor,channel in zip(factors,channels):
data = channel.frames[pos:pos+sampwidth]
data = audioutils.unpack_data(data, sampwidth)
# without a cast, sum is a float!
sampsum += data[0]*factor*attenuator
# truncate the values if there is clipping
if sampsum < 0:
return max(sampsum,minval)
elif sampsum > 0:
return min(sampsum,maxval)
return 0
