PyAudio not capturing correct audio data

Question

I can't get a PyAudio stream to capture audio data from my USB microphone.

I'm running a Python program on Ubuntu trusty (Ubuntu 14.04.3 LTS). I've configured ALSA to set my USB microphone as the default sound card, and tested that this work's properly by running:

arecord -D plughw:0,0 -f cd test.wav

and then playing that audio back using

aplay -D plughw:0,0 test.wav

My /etc/modprobe.d/alsa-base.conf file looks like this:

# autoloader aliases
install sound-slot-0 /sbin/modprobe snd-card-0
install sound-slot-1 /sbin/modprobe snd-card-1
install sound-slot-2 /sbin/modprobe snd-card-2
install sound-slot-3 /sbin/modprobe snd-card-3
install sound-slot-4 /sbin/modprobe snd-card-4
install sound-slot-5 /sbin/modprobe snd-card-5
install sound-slot-6 /sbin/modprobe snd-card-6
install sound-slot-7 /sbin/modprobe snd-card-7

# Cause optional modules to be loaded above generic modules
install snd /sbin/modprobe --ignore-install snd $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-ioctl32 ; /sbin/modprobe --quiet --use-blacklist snd-seq ; }
#
# Workaround at bug #499695 (reverted in Ubuntu see LP #319505)
install snd-pcm /sbin/modprobe --ignore-install snd-pcm $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-pcm-oss ; : ; }
install snd-mixer /sbin/modprobe --ignore-install snd-mixer $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-mixer-oss ; : ; }
install snd-seq /sbin/modprobe --ignore-install snd-seq $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-seq-midi ; /sbin/modprobe --quiet --use-blacklist snd-seq-oss ; : ; }
#
install snd-rawmidi /sbin/modprobe --ignore-install snd-rawmidi $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-seq-midi ; : ; }
# Cause optional modules to be loaded above sound card driver modules
install snd-emu10k1 /sbin/modprobe --ignore-install snd-emu10k1 $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-emu10k1-synth ; }
install snd-via82xx /sbin/modprobe --ignore-install snd-via82xx $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist snd-seq ; }

# Load saa7134-alsa instead of saa7134 (which gets dragged in by it anyway)
install saa7134 /sbin/modprobe --ignore-install saa7134 $CMDLINE_OPTS && { /sbin/modprobe --quiet --use-blacklist saa7134-alsa ; : ; }
# Prevent abnormal drivers from grabbing index 0
options bt87x index=-2
options cx88_alsa index=-2
options saa7134-alsa index=-2
options snd-atiixp-modem index=-2
options snd-intel8x0m index=-2
options snd-via82xx-modem index=-2
# options snd-usb-audio index=-2
options snd-usb-audio index=0
options snd-usb-caiaq index=-2
options snd-usb-ua101 index=-2
options snd-usb-us122l index=-2
options snd-usb-usx2y index=-2
# Ubuntu #62691, enable MPU for snd-cmipci
options snd-cmipci mpu_port=0x330 fm_port=0x388
# Keep snd-pcsp from being loaded as first soundcard
options snd-pcsp index=-2

I've installed PyAudio successfully, however when I open a stream, I don't get any audio data. My understanding is that the default device is used when opening a stream with PyAudio (unless otherwise specified by the input_device_index argument which I am not setting).

    p = pyaudio.PyAudio()
    stream = p.open(
        format=pyaudio.paInt16,
        channels=1,
        rate=18000,
        input=True,
        frames_per_buffer=1024
    )

When I run PyAudio().get_device_info_by_index(0), I get:

{'defaultSampleRate': 16000.0, 'defaultLowOutputLatency': 0.0239375, 'defaultLowInputLatency': 0.0239375, 'maxInputChannels': 1L, 'structVersion': 2L, 'hostApi': 0L, 'index': 0, 'defaultHighOutputLatency': 0.096, 'maxOutputChannels': 2L, 'name': u'Jabra SPEAK 410 USB: Audio (hw:0,0)', 'defaultHighInputLatency': 0.096}

^ that (Jabra SPEAK 410 USB: Audio) is my USB mic.

These are the logs PyAudio is spitting out when it is loaded (before the stream is even opened). I've read online, though, that I can ignore most of those errors.

ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.hdmi.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM hdmi
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.hdmi.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM hdmi
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline:CARD=0,DEV=0
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline:CARD=0,DEV=0
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM phoneline
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4248:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:4727:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM phoneline
bt_audio_service_open: connect() failed: Connection refused (111)
bt_audio_service_open: connect() failed: Connection refused (111)
bt_audio_service_open: connect() failed: Connection refused (111)
bt_audio_service_open: connect() failed: Connection refused (111)
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started

It looks like the stream is collecting data when it's opened, but it is not capture any sound. My mic is turned on, unmuted, and set to capture audio at a level of 86.

I'm thinking it somehow the default device isn't being set properly (with ALSA), because when I do:

arecord test.wav

and

aplay test.wav

nothing gets recorded.

Answer 1

Figured it out. It looks like Ubuntu comes with PulseAudio and ALSA. And PulseAudio was hijacking the default device spot.

This is a bit' rigid, but I just removed PulseAudio completely and the issues went away.

sudo apt-get autoremove pulseaudio