My goal is to do spectrum analysis of a gear motor. I used Python with the Pyaudio package and made a crude spectrum analyzer that displays the FFT as the sound is being recorded. I recorded 10 seconds of sound just for test. Sample rate is 44100, each frame is 1024 samples. For each frame I plotted the FFT, and made a dynamic plot thru the 10 seconds.
I also downloaded a FFT analyzer to my smartphone and compared the results as I turned on a motor. The smartphone app is able to display relatively stable spectrum. In my plot, the magnitudes are very high upon turning on the motor, and only "settled" after a couple of seconds.
I wonder why that is. Is it due to my sound card or laptop mic? I tested using another laptop and got similar result. Is it because I recorded in Mono mode? The spectrum changes too much as I move the motor around, whereas on the smartphone the spectrum is more stable.
Or is it because I didn't use a Window function? Here is my code:
import numpy as np
import os
import time
import pyaudio
import matplotlib.pyplot as plt
from scipy.fftpack import fft
CHUNK = 1024
FORMAT = pyaudio.paInt16
CHANNELS = 1
RATE = 44100
RECORD_SECONDS = 10
WAVE_OUTPUT_FILENAME = "test.wav"
p = pyaudio.PyAudio()
stream = p.open(format=FORMAT,
channels=CHANNELS,
rate=RATE,
input=True,
frames_per_buffer=CHUNK)
input('Press key to start recording:\n')
print('1 sec delay started') #delay so keystroke doesn't get recorded
time.sleep(1)
print("* recording")
frames = []
n = 1024
k=np.arange(n)
T = n/RATE
frq = k/T
frq = frq[range(int(n/2))] # one side frequency range
for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
data = stream.read(CHUNK)
frames.append(data)
decoded = np.fromstring(data, dtype=np.int16) #grab the data in stream
fft_decode=fft(decoded)/(len(decoded)/2) #normalized FFT
mags=np.absolute(fft(decoded)) #
plt.ylim(top=55000)
plt.xlabel('Freq (Hz)')
plt.ylabel('|Y(freq)|')
plt.plot(frq, mags[range(int(n/2))],'b')
plt.pause(.01)
plt.gcf().clear()
print("* done recording")
plt.close()
How can I improve my analyzer? Is there anything wrong with my code or the way I approached this?
Edit: Nevermind. The reason turns out to be the boost function of my microphone, and disabling it solved my problem.