Using PyAudio breaks GPIO18 PWM mode ? (driving LED strip with rpi_ws281x and listening MIC with PyAudio) [RPi Model B 512MB ARMv6]

Question

I'm trying to drive a RGB LED strip with RPI's GPIO18 in python with rpi_ws281x library while listening to USB Microphone connected to the RPI to finally send colors depending on audio frequencies captured.

Problem: the LED strip works fine UNTIL i instanciate the pyAudio Object. As soon as I execute the following instructions:

>>> import pyaudio
>>> p = pyaudio.PyAudio() # <-- after this instruction the LED strip is KO

After that instruction the LED strip blocks or displays random colors. PyAudio outputs some messages see at the end of this post.

Is there an incompatiblity between GPIO18 in PWM mode and PyAudio ?

Any help would be appreciated, and Merry Christmas All!

Notes:

• I use the strandtest.py script to test the led strip (see reference below). This script works great.
• Recording microphone manually with arecord command while LED strip is being driven by strandtest.py works great too
• PyAudio input mode works. I managed to get audio frequencies with fft.

References:

(NeoPixel sample wiring)[https://learn.adafruit.com/neopixels-on-raspberry-pi/wiring]

(rpi_ws281x strandtest)[https://github.com/jgarff/rpi_ws281x/blob/master/python/examples/strandtest.py]

PyAudio's messages:

ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.front.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM front
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.bcm28                                   35.pcm.surround51.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround21
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround51.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround21
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround40.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround40
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround51.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround41
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround51.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround50
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround51.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround51
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.surround71.0:CARD=0'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM surround71
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM iec958
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM spdif
ALSA lib confmisc.c:1286:(snd_func_refer) Unable to find definition 'cards.bcm28                                   35.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4259:(_snd_config_evaluate) function snd_func_refer returned err                                   or: No such file or directory
ALSA lib conf.c:4738:(snd_config_expand) Evaluate error: No such file or directo                                   ry
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM spdif
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
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

Answer 1

Both PyAudio and rpi_ws281x are using a single hardware PWM peripheral in an inconsistent fashion. Of course it does not work.

You need to change one of them to not use the hardware PWM peripheral.

I'd have thought the LED strips could be driven by the hardware PCM peripheral rather than the hardware PWM peripheral.