ubuntu语音库ALSA报错具体原因

在ubuntu中使用pyaudio或portaudio时总会有下面的提示，不胜其烦。

ALSA lib pcm_dsnoop.c:612:(snd_pcm_dsnoop_open) unable to open slave
ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm_dmix.c:957:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave

后来才知道这不是报错，具体解释见PyAudio、PortAudio 和 ALSA 消息