How do I generate a sine wave using Python?

Question

I'm trying to generate a sine wave of a given frequency for a given duration and then write it into a .wav file. I'm using numpy's sin function and scipy's wavfile function. I'm getting a weird sound that is definitely not a sine wave.

import numpy as np
from scipy.io import wavfile

fs = 44100

f = int(raw_input("Enter fundamental frequency: "))
t = float(raw_input("Enter duration of signal (in seconds): "))

samples = np.arange(t * fs)

signal = np.sin(2 * np.pi * f * samples)

signal *= 32767

signal = np.int16(signal)

wavfile.write(str(raw_input("Name your audio: ")), fs, signal)

Any help would be appreciated. Have I made some fundamentally incorrect assumption about sine waves or something?

Answer 1

Change

samples = np.arange(t * fs)

to

samples = np.linspace(0, t, int(fs*t), endpoint=False)

(This assumes that fs*t results in an integer value.)

Or, as Paul Panzer suggests in a comment,

samples = np.arange(t * fs) / fs

Your samples was just the sequence of integers 0, 1, 2, ... fs*t. Instead, you need the actual time values (in seconds) of the samples.

Answer 2

You are mixing sample value and length! Try:

samples = np.linspace(0, t, t * fs)

Another detail: you don't need the str around raw_input.

Answer 3

Use this and set the parameters as you want

start_time = 0
end_time = 1
sample_rate = 1000
time = np.arange(start_time, end_time, 1/sample_rate)
theta = 0
frequency = 100
amplitude = 1
sinewave = amplitude * np.sin(2 * np.pi * frequency * time + theta)
figure(figsize=(20, 6), dpi=80)
plt.plot(sinewave)

Answer 4

A simplified approach:

cycles = 2 # how many sine cycles
resolution = 25 # how many datapoints to generate

length = np.pi * 2 * cycles
my_wave = np.sin(np.arange(0, length, length / resolution))

Generates:

[ 0.      0.4818  0.8443  0.998   0.9048  0.5878  0.1253 -0.3681 -0.7705
 -0.9823 -0.9511 -0.6845 -0.2487  0.2487  0.6845  0.9511  0.9823  0.7705
  0.3681 -0.1253 -0.5878 -0.9048 -0.998  -0.8443 -0.4818]

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Note: Leaving this answer here despite not addressing sine wave for audio generation, since I found that for my application it was more intuitive to only parameterise length of the wave and number of datapoints generated, as opposed to fundamental frequency and duration in seconds.