Read microphones connected to 4x1 USB Hub using Python

Question

I'm working on a sound source localization project which needs an array of microphones. I have 4 microphones with an Audio Jack plug which is connected to a USB Audio adapter. Last I use a 4x1 USB Hub to connect all the microphone-adapter components to my PC to read the incoming signal using Python PyAudio module.

Here is my configuration:

Here is my Python code:

import pyaudio
import wave

CHUNK = 2
FORMAT = pyaudio.paInt16
CHANNELS = 1
RATE = 8900
RECORD_SECONDS = 2
WAVE_OUTPUT_FILENAME = "output.wav"
NUM_OF_MICS = 4

p = pyaudio.PyAudio()

# Create a stream for each microphone with the IDs 1,2,3,4
streams = [p.open(format=FORMAT,
                  channels=CHANNELS,
                  rate=RATE,
                  input=True,
                  frames_per_buffer=CHUNK,
                  input_device_index=idx) for idx in range(1, NUM_OF_MICS + 1)]

print("* recording")

# Record 2 seconds of Audio for each
frames = []
for j in range(NUM_OF_MICS):
    row = []
    for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
        row.append(streams[j].read(CHUNK, exception_on_overflow=False))
    frames.append(row)

for stream in streams:
    stream.stop_stream()
    stream.close()

p.terminate()

print("* done recording")

# Save audio with the names {1,2,3,4}_output.wav
for j in range(NUM_OF_MICS):
    wf = wave.open(str(j) + "_" + WAVE_OUTPUT_FILENAME, 'wb')
    wf.setnchannels(CHANNELS)
    wf.setsampwidth(p.get_sample_size(FORMAT))
    wf.setframerate(RATE)
    wf.writeframes(b''.join(frames[j]))
    wf.close()

Looking at the problem, I am able to read the microphone outputs clearly when I select just one of them and start recording only using it. However, when I process the code above, the recordings with the names {0,2}_output.wav sounds okay, but the others - {1,3}_output.wav contain only messy sound (at least it is what I hear).

I have tested all the plugs and devices separately, and all of them work. I am open to suggestions.

Edit 1:

When I connect only 2 Microphones to HUB and set the variable NUM_OF_MICS = 2 I get both sounds, {0,1}_output.wav, as normal.

Edit 2

Inspired by the comment of @MarcusMüller, I recorded sound from Mics by multithreading. Again at least one of the saved sounds is just noise.

Here is the code:

# coding=utf-8
# Python3.6
# Class Record a wav in new thread
# Author:Why
# Date:2018.04.23

import threading
import pyaudio
import wave


class RecordThread(threading.Thread):
    def __init__(self, idx, audiofile='record.wav'):
        threading.Thread.__init__(self)
        self.bRecord = True
        self.audiofile = audiofile
        self.chunk = 1024
        self.format = pyaudio.paInt16
        self.channels = 1
        self.rate = 16000
        self.idx = idx

    def run(self):
        audio = pyaudio.PyAudio()
        wavfile = wave.open(self.audiofile, 'wb')
        wavfile.setnchannels(self.channels)
        wavfile.setsampwidth(audio.get_sample_size(self.format))
        wavfile.setframerate(self.rate)
        wavstream = audio.open(format=self.format,
                               channels=self.channels,
                               rate=self.rate,
                               input=True,
                               frames_per_buffer=self.chunk,
                               input_device_index=self.idx)

        while self.bRecord:
            wavfile.writeframes(wavstream.read(self.chunk))
        wavstream.stop_stream()
        wavstream.close()
        audio.terminate()

    def stoprecord(self):
        self.bRecord = False


from time import sleep

audio_record_threads = [RecordThread(idx=i, audiofile=str(i) + '_output.wav') for i in range(1, 4)]
# start
for thd in audio_record_threads:
    thd.start()
sleep(5)
for thd in audio_record_threads:
    thd.stoprecord()