\"\"\" guitar_string.py Models a guitar string. \"\"\" import math import random

Question

"""
guitar_string.py

Models a guitar string.
"""

import math
import random
import ring_buffer
import stdarray
import stdio
import sys

# Sampling rate.
SPS = 44100

def create(frequency):
"""
Create and return a guitar string of the given frequency, using a sampling
rate given by SPS. A guitar string is represented as a ring buffer of
of capacity N (SPS divided by frequency, rounded up to the nearest
integer), with all values initialized to 0.0.
"""

...

def create_from_samples(init):
"""
Create and return a guitar string whose size and initial values are given
by the list init.
"""

...

def pluck(string):
"""
Pluck the given guitar string by replacing the buffer with white noise.
"""

...

def tic(string):
"""
Advance the simulation one time step on the given guitar string by applying
the Karplus-Strong update.
"""

...

def sample(string):
"""
Return the current sample from the given guitar string.
"""

...

def _main():
"""
Test client [DO NOT EDIT].
"""

N = int(sys.argv[1])
samples = [.2, .4, .5, .3, -.2, .4, .3, .0, -.1, -.3]
test_string = create_from_samples(samples)
for t in range(N):
stdio.writef('%6d %8.4f ', t, sample(test_string))
tic(test_string)

if __name__ == '__main__':
_main()

Problem 2. (Guitar String) Next, create a module guitar-string.py to model a vibrating guitar string. The module must implement the following API: function description create and return a guitar string of the given frequency, using a sampling create(frequency) rate given by SPS, a constant in guitar-string-Py create-from-samples(init) create and return a guitar string whose size and initial values are given by the list init pluck the given guitar string by replacing the buffer with white noise pluck (string) advance the simulation one time step on the given guitar string by tic (string) applying the Karplus-Strong update current sample from the given guitar string sample (string) Some details about the functions: create (frequency) creates and returns a ring buffer of capacity N (sampling rate 44,100 divided by frequency, rounded up to the nearest integer), and initializes it to represent a guitar string at rest by emqueueing N zeros. A guitar string is represented as a ring buffer of capacity N, with all values initialized to 0.0 create from samples (init) creates and returns a ring buffer of capacity equal to the size of the given list init, and initializes the contents of the buffer to the values in the list. In this assignment, this function's main purpose is for debugging and grading. pluck (string replaces the N items in the ring buffer string with N random values between -0.5 and 0.5. tic (string) applies the Karplus-Strong update: deletes the sample at the front of the ring buffer string and adds to the end of the ring buffer the average of the first two samples, multiplied by the energy decay factor. sample (string) returns the value of the item at the front of the ring buffer string. Python guitar-string. py 25 0 0.2000 1 0.4000 2 0.5000 3 0.3000 4 0.2000 5 0.4000 6 0.3000 7 0.0000 8 0.1000 9 0.3000 10 0.2988 11 0.4482 12 0.3984 13 0.0498 14 0.0996 16 0.1494 17 0.0498 18 0.1992 19 0.0006 20 0.3720 21 0.4216 22 0.2232

Explanation / Answer

""" guitar_string.py Models a guitar string. """ import math import random import ring_buffer import stdarray import stdio import sys # Sampling rate. SPS = 44100 def create(frequency): """ Create and return a guitar string of the given frequency, using a sampling rate given by SPS. A guitar string is represented as a ring buffer of of capacity N (SPS divided by frequency, rounded up to the nearest integer), with all values initialized to 0.0. """ string = [0.0]*int(SPS/frequency) return string def create_from_samples(init): """ Create and return a guitar string whose size and initial values are given by the list init. """ gs = init return gs def pluck(string): """ Pluck the given guitar string by replacing the buffer with white noise. """ for x in string: x = random.uniform(-0.5, 0.5) def tic(string): """ Advance the simulation one time step on the given guitar string by applying the Karplus-Strong update. """ x = string.pop(0) y = string[0] string.append(.996 * 0.5*(x + y)) def sample(string): """ Return the current sample from the given guitar string. """ return string[0] def _main(): """ Test client [DO NOT EDIT]. """ N = int(sys.argv[1]) samples = [.2, .4, .5, .3, -.2, .4, .3, .0, -.1, -.3] test_string = create_from_samples(samples) for t in range(N): stdio.writef('%6d %8.4f ', t, sample(test_string)) tic(test_string) if __name__ == '__main__': _main()

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