在树莓派pi3上的python中使用8khz采样率

Question

I'm trying to record voice from USB microphone in 8Khz with my rpi3 using python. I used pyaudio, sounddevice, and soundfile libraries but they only let me sample in 44100Hz or 48000Hz. When I tried to sample in 8KHz I got the following error:

"PortAudioError: Error opening InputStream: Invalid sample rate".

On the other hand when I used the command:

"arecord -D plughw:1,0 -f S16_LE -r 8000 -d 2 test.wav" 

in the command-line everything was fine.

This is the code I used:

import pyaudio
import wave

FORMAT = pyaudio.paInt16




CHANNELS = 1
RATE = 8000
CHUNK = 4000
RECORD_SECONDS = 5
WAVE_OUTPUT_FILENAME = "test1.wav"

audio = pyaudio.PyAudio()
print audio.get_default_input_device_info()


# start Recording
stream = audio.open(format=FORMAT, channels=CHANNELS,rate=RATE, input=True,frames_per_buffer=CHUNK,input_device_index=1)
print ("recording...")
frames = []

for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
    data = stream.read(CHUNK)
    frames.append(data) 
print ("finished recording")


# stop Recording
stream.stop_stream()
stream.close()
audio.terminate()



waveFile = wave.open(WAVE_OUTPUT_FILENAME, 'wb')
waveFile.setnchannels(CHANNELS)
waveFile.setsampwidth(audio.get_sample_size(FORMAT))
waveFile.setframerate(RATE)
waveFile.writeframes(b''.join(frames))
waveFile.close()

This is the result:

{'defaultSampleRate': 44100.0, 'defaultLowOutputLatency': -1.0, 'defaultLowInputLatency': 0.008684807256235827, 'maxInputChannels': 1L, 'structVersion': 2L, 'hostApi': 0L, 'index': 1L, 'defaultHighOutputLatency': -1.0, 'maxOutputChannels': 0L, 'name': u'USB PnP Sound Device: Audio (hw:1,0)', 'defaultHighInputLatency': 0.034829931972789115}

Traceback (most recent call last):
  File "/home/pi/wave1.py", line 20, in <module>
    stream = audio.open(format=FORMAT, channels=CHANNELS,rate=RATE, input=True,frames_per_buffer=CHUNK,input_device_index=1)
  File "build/bdist.linux-armv7l/egg/pyaudio.py", line 750, in open
    stream = Stream(self, *args, **kwargs)
  File "build/bdist.linux-armv7l/egg/pyaudio.py", line 441, in __init__
    self._stream = pa.open(**arguments)
IOError: [Errno -9997] Invalid sample rate

I checked and i know that I'm using the right device, but as you can see the default sample rate didn't change and I still get the same error.

Answer 1

You could be opening the wrong device in your Python script. The available sample rates are determined by your hardware, and the one being opened in PyAudio does not support 8kHz, whereas the one you are opening using arecord clearly does. The different API's available under Linux seem to index the hardware differently and it can be very confusing (I've certainly found it so).

On my Pi, the USB mic is device 2, and I am sampling at 44.1kHz, so I have:

import pyaudio

DEVICE = 2 #USB Audio Device
CHANNELS = 1
FRAME_RATE = 44100
FORMAT = pyaudio.paInt16

def init_stream():
    stream = p.open(format = FORMAT,
                    channels = CHANNELS, 
                    rate = FRAME_RATE, 
                    input = True,
                    output = False,
                    input_device_index = DEVICE,
                    frames_per_buffer = 8192,
                    stream_callback = callback)
    return (stream)

To get a list of the audio devices, as indexed by PyAudio (and so select the correct device), you can use the code in this answer.