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

# [exercises](reproduction.ipynb)

# In[1]:


get_ipython().run_line_magic('matplotlib', 'inline')
import matplotlib.pyplot as plt
import numpy as np
import sfs


# In[2]:


grid = sfs.util.xyz_grid([-2, 2], [-2, 2], 0, spacing=0.02)


# In[3]:


x0 = 0, 1.5, 0
f = 1000  # Hz
omega = 2 * np.pi * f


# In[4]:


p_point = sfs.mono.source.point(omega, x0, None, grid)
p_point *= 4 * np.pi
sfs.plot.soundfield(p_point, grid)
plt.title("Point Source at {} m".format(x0));


# In[5]:


x0 = 0, 1.5
f = 1000  # Hz
omega = 2 * np.pi * f


# In[6]:


p_line = sfs.mono.source.line(omega, x0, None, grid)
p_line *= np.sqrt(8 * np.pi * omega / sfs.defs.c) * np.exp(1j * np.pi / 4)
sfs.plot.soundfield(p_line, grid)
plt.title("Line Source at {} m".format(x0[:2]));


# Difference between point source and line source:
# When doubling the distance, the sound level of a ...
# 
# * ... point source is attenuated by 6 dB
# 
# * ... line source is attenuated by 3 dB

# In[7]:


x0 = 0, 1.5, 0
n0 = 0, -1, 0
f = 1000  # Hz
omega = 2 * np.pi * f


# In[8]:


p_plane = sfs.mono.source.plane(omega, x0, n0, grid)
sfs.plot.soundfield(p_plane, grid);
plt.title("Plane wave with $n_0 =$ {}".format(n0));


# From this snapshot, it's not possible to recognize if the plane wave is travelling up or down.
# One would need an animation of some kind to see the direction of propagation (this was a trick question!).
# 
# The level doesn't decay over distance (another trick question!).

# If the weighting factors are equal, the phantom source is halfway between the two loudspeakers.
# 
# TODO: intensity stereophony, time-of-arrival stereophony

# Reason for artifacts: spatial aliasing.
# 
# TODO: 2.5 D

# WFS vs. NFC-HOA artifacts: HOA has a circular area (shrinking with higher frequencies) in the center without aliasing, but around that area the artifacts are stronger than in WFS.

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