CODEWITHSUNDEEP
pythonwavwave
kotek
kotek

Reputation: 31

something strange is happening with the WAV sound recording

I want to make my own analogue for SSTV and I ran into a problem: when I start recording fast-changing beeps (which are 5 milliseconds long), very strange extra sounds appear

For creating beeps i used wave, math and struct library (solve to creating beeps)

So, when I started this code, I received this file with VERY strange sounds: (click to hear)

import math
import wave
import struct

audio = []
sample_rate = 44100.0

def append_sinewave(freq=440.0, duration_milliseconds=500): # i removed volume from example
    global audio
    num_samples = duration_milliseconds * (sample_rate / 1000.0)
    for x in range(int(num_samples)):
        #audio.append(volume * math.sin(2 * math.pi * freq * ( x / sample_rate )))
        audio.append(math.sin(2 * math.pi * freq * ( x / sample_rate )))
    return

def save_wav(file_name):
    wav_file=wave.open(file_name,"w")
    nchannels = 1
    sampwidth = 2
    nframes = len(audio)
    comptype = "NONE"
    compname = "not compressed"
    wav_file.setparams((nchannels, sampwidth, sample_rate, nframes, comptype, compname))
    for sample in audio:
        wav_file.writeframes(struct.pack('h', int( sample * 32767.0 )))
    wav_file.close()
    return

for i in range(1000): # creating sound
    append_sinewave(freq=400+5*i, duration_milliseconds=5)

save_wav("output.wav")

Also, when I increasing duration of beeps (see code below) this strange sounds disappeared (click to hear)

for i in range(20): # more duration fixes the problem
    append_sinewave(freq=400+250*i, duration_milliseconds=250)

save_wav("output.wav")

How to fix it?

Upvotes: 0

Views: 36

Answers (1)

kotek
kotek

Reputation: 31

For solve my problem, I made the beginning of the wave from the previous frequency, and and because of this, the very claps that spoiled the sound disappeared. Solution in the code:

# we need to edit only append_sinewave function
audio = []
sample_rate = 44100.0
last_phase = 0  # a variable to save the phase between beeps

def append_sinewave(freq=440.0, duration_milliseconds=500):
    global audio, last_phase
    num_samples = int(duration_milliseconds * (sample_rate / 1000.0))
    
    # adding a signal while continuing the phase
    for x in range(num_samples):
        phase = last_phase + 2 * math.pi * freq * (x / sample_rate)
        sample = math.sin(phase)
        audio.append(sample)
    
    # save the phase so that the next frequency continues the wave
    last_phase += 2 * math.pi * freq * (num_samples / sample_rate)
    last_phase %= 2 * math.pi  # normalizing
    return

Thanks to OysterShucker for idea

Upvotes: 1

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