#!/usr/bin/env python
# coding: utf-8

# In[1]:


import numpy, scipy, matplotlib.pyplot as plt, urllib, IPython.display
plt.rcParams['figure.figsize'] = (14,5)


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# # Zero Crossing Rate

# The [zero crossing rate](https://en.wikipedia.org/wiki/Zero-crossing_rate) indicates the number of times that a signal crosses the horizontal axis.

# Let's load a signal:

# In[2]:


x, fs = librosa.load('simple_loop.wav')


# Listen to the signal:

# In[3]:


IPython.display.Audio(x, rate=fs)


# Plot the signal:

# In[4]:


librosa.display.waveplot(x, sr=fs)


# Let's zoom in:

# In[5]:


plt.plot(x[1500:2000])


# I count three zero crossings. Let's compute the zero crossings using librosa.

# In[6]:


zero_crossings = librosa.zero_crossings(x[1500:2000], pad=False)


# That computed each individual zero crossing. To find the total number of zero crossings, use `sum`:

# In[7]:


print sum(zero_crossings)


# To find the zero-crossing *rate* over time, use `zero_crossing_rate`:

# In[8]:


zcrs = librosa.feature.zero_crossing_rate(x)
print zcrs.shape


# Plot the zero-crossing rate:

# In[9]:


plt.plot(zcrs[0])


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