CODEWITHSUNDEEP
pythonaudioraspberry-piaudio-recordingpyaudio
user2417339
user2417339

Reputation:

Unable to change card index in PyAudio on Raspberry pi

I have attached a USB up to a RPi and know it works because I am able to record audio through the microphone using the command:

arecord test.wav -D sysdefault:CARD=1

Now I want to write a Python program that can stream the data from the usb device. I wrote the following code (which sets the input_device_index = 1 in the .open()):

import pyaudio
import numpy as np

RATE = 44100
CHUNK = 1024

p = pyaudio.PyAudio()

stream = p.open(format=pyaudio.paInt16, channels=1, rate=RATE, input=True, input_device_index=1, frames_per_buffer=CHUNK)

while (True):
    data = np.fromstring(stream.read(CHUNK),dtype=np.int16)

stream.stop_stream()
stream.close()
p.terminate()

When I run the code I get the following error though:

"ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.bcm2835.pcm.front.0:CARD=0'
ALSA lib conf.c:4528:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5007:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM front
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.bcm2835.pcm.surround51.0:CARD=0'  
.........  
a failed in 'src/hostapi/alsa/pa_linux_alsa.c', line: 2818
Traceback (most recent call last):
  File "RealTimePlaybackTest.py", line 9, in <module>
    stream = p.open(format=pyaudio.paInt16, channels=1, rate=RATE, input=True, input_device_index=1, frames_per_buffer=CHUNK)
  File "build/bdist.linux-armv7l/egg/pyaudio.py", line 750, in open
  File "build/bdist.linux-armv7l/egg/pyaudio.py", line 441, in __init__
IOError: [Errno -9998] Invalid number of channels

"The whole error is in this gist
This confuses me though because the error states that the CARD=0 even though I set the index = 1 in the code. How can I go about changing it so the CARD=1?

Upvotes: 2

Views: 1750

Answers (2)

nsteffensen
nsteffensen

Reputation: 33

You can get the Card and Device number for all capture devices using

arecord -l

My USB mic lists as

card 1: Device [USB PnP Sound Device], device 0: USB Audio [USB Audio]

The Card is specified in

/usr/share/alsa/alsa.conf

So for my capture device on Card 1, I set this

defaults.ctl.card 1
defaults.pcm.card 1

As you noted, the Device number is specified in the call to open a stream; p.open(input_device_index=0).

Upvotes: 2

user2417339
user2417339

Reputation:

I found the solution. Card number is not the same as index number. I needed to run the following code to get the index number:

import pyaudio
p = pyaudio.PyAudio()
for i in range(p.get_device_count()):
  dev = p.get_device_info_by_index(i)
  print((i,dev['name'],dev['maxInputChannels']))

Upvotes: 1

Related Questions