ALSA Mics

ALSA Microphones

Device Compatibility

Overview

The following sections will go over how to read microphone data from your MATRIX device. Note the code below isn't actually part of MATRIX Lite, but a downloadable library that allows us to easily access ALSA microphones.

Dependencies

Install the MATRIX Kernel Modules.

Install portaudio. 

sudo apt install portaudio19-dev

Install pyaudio. 

sudo python3 -m pip install pyaudio

Configure your Pi's asound.conf file.

Due to the linux kernel being recently updated, the playback rate for the Raspberry Pi must be set to 16000. Add the following highlighted line to /etc/asound.conf

pcm.speaker {
  type plug
  slave {
    pcm "hw:0,0"
    rate 16000
  }
}

Recording Example

Below is a simple example that shows you how to create an audio recording with pyaudio. Visit the pyaudio documentation for a complete overview.

recordFile.py

Be sure to run the example with python3

import pyaudio
import wave

# recording configs
CHUNK = 2048
FORMAT = pyaudio.paInt16
CHANNELS = 8
RATE = 96000
RECORD_SECONDS = 5
WAVE_OUTPUT_FILENAME = "output.wav"

# create & configure microphone
mic = pyaudio.PyAudio()
stream = mic.open(format=FORMAT,
                channels=CHANNELS,
                rate=RATE,
                input=True,
                frames_per_buffer=CHUNK)

print("* recording")

# read & store microphone data per frame read
frames = []
for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
    data = stream.read(CHUNK)
    frames.append(data)

print("* done recording")

# kill the mic and recording
stream.stop_stream()
stream.close()
mic.terminate()

# combine & store all microphone data to output.wav file
outputFile = wave.open(WAVE_OUTPUT_FILENAME, 'wb')
outputFile.setnchannels(CHANNELS)
outputFile.setsampwidth(mic.get_sample_size(FORMAT))
outputFile.setframerate(RATE)
outputFile.writeframes(b''.join(frames))
outputFile.close()

Once recorded, you can play the audio through the Pi's audio jack with: 

# raise the output volume to max
amixer set PCM 100%

# play the file
aplay output.wav

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