Tutorial :Detect & Record Audio in Python



Question:

I need to capture audio clips as WAV files that I can then pass to another bit of python for processing. The problem is that I need to determine when there is audio present and then record it, stop when it goes silent and then pass that file to the processing module.

I'm thinking it should be possible with the wave module to detect when there is pure silence and discard it then as soon as something other than silence is detected start recording, then when the line goes silent again stop the recording.

Just can't quite get my head around it, can anyone get me started with a basic example.


Solution:1

As a follow up to Nick Fortescue's answer, here's a more complete example of how to record from the microphone and process the resulting data:

from sys import byteorder  from array import array  from struct import pack    import pyaudio  import wave    THRESHOLD = 500  CHUNK_SIZE = 1024  FORMAT = pyaudio.paInt16  RATE = 44100    def is_silent(snd_data):      "Returns 'True' if below the 'silent' threshold"      return max(snd_data) < THRESHOLD    def normalize(snd_data):      "Average the volume out"      MAXIMUM = 16384      times = float(MAXIMUM)/max(abs(i) for i in snd_data)        r = array('h')      for i in snd_data:          r.append(int(i*times))      return r    def trim(snd_data):      "Trim the blank spots at the start and end"      def _trim(snd_data):          snd_started = False          r = array('h')            for i in snd_data:              if not snd_started and abs(i)>THRESHOLD:                  snd_started = True                  r.append(i)                elif snd_started:                  r.append(i)          return r        # Trim to the left      snd_data = _trim(snd_data)        # Trim to the right      snd_data.reverse()      snd_data = _trim(snd_data)      snd_data.reverse()      return snd_data    def add_silence(snd_data, seconds):      "Add silence to the start and end of 'snd_data' of length 'seconds' (float)"      r = array('h', [0 for i in xrange(int(seconds*RATE))])      r.extend(snd_data)      r.extend([0 for i in xrange(int(seconds*RATE))])      return r    def record():      """      Record a word or words from the microphone and       return the data as an array of signed shorts.        Normalizes the audio, trims silence from the       start and end, and pads with 0.5 seconds of       blank sound to make sure VLC et al can play       it without getting chopped off.      """      p = pyaudio.PyAudio()      stream = p.open(format=FORMAT, channels=1, rate=RATE,          input=True, output=True,          frames_per_buffer=CHUNK_SIZE)        num_silent = 0      snd_started = False        r = array('h')        while 1:          # little endian, signed short          snd_data = array('h', stream.read(CHUNK_SIZE))          if byteorder == 'big':              snd_data.byteswap()          r.extend(snd_data)            silent = is_silent(snd_data)            if silent and snd_started:              num_silent += 1          elif not silent and not snd_started:              snd_started = True            if snd_started and num_silent > 30:              break        sample_width = p.get_sample_size(FORMAT)      stream.stop_stream()      stream.close()      p.terminate()        r = normalize(r)      r = trim(r)      r = add_silence(r, 0.5)      return sample_width, r    def record_to_file(path):      "Records from the microphone and outputs the resulting data to 'path'"      sample_width, data = record()      data = pack('<' + ('h'*len(data)), *data)        wf = wave.open(path, 'wb')      wf.setnchannels(1)      wf.setsampwidth(sample_width)      wf.setframerate(RATE)      wf.writeframes(data)      wf.close()    if __name__ == '__main__':      print("please speak a word into the microphone")      record_to_file('demo.wav')      print("done - result written to demo.wav")  


Solution:2

I believe the WAVE module does not support recording, just processing existing files. You might want to look at PyAudio for actually recording. WAV is about the world's simplest file format. In paInt16 you just get a signed integer representing a level, and closer to 0 is quieter. I can't remember if WAV files are high byte first or low byte, but something like this ought to work (sorry, I'm not really a python programmer:

from array import array    # you'll probably want to experiment on threshold  # depends how noisy the signal  threshold = 10   max_value = 0    as_ints = array('h', data)  max_value = max(as_ints)  if max_value > threshold:      # not silence  

PyAudio code for recording kept for reference:

import pyaudio  import sys    chunk = 1024  FORMAT = pyaudio.paInt16  CHANNELS = 1  RATE = 44100  RECORD_SECONDS = 5    p = pyaudio.PyAudio()    stream = p.open(format=FORMAT,                  channels=CHANNELS,                   rate=RATE,                   input=True,                  output=True,                  frames_per_buffer=chunk)    print "* recording"  for i in range(0, 44100 / chunk * RECORD_SECONDS):      data = stream.read(chunk)      # check for silence here by comparing the level with 0 (or some threshold) for       # the contents of data.      # then write data or not to a file    print "* done"    stream.stop_stream()  stream.close()  p.terminate()  


Solution:3

Thanks to cryo for improved version that I based my tested code below:

#Instead of adding silence at start and end of recording (values=0) I add the original audio . This makes audio sound more natural as volume is >0. See trim()  #I also fixed issue with the previous code - accumulated silence counter needs to be cleared once recording is resumed.    from array import array  from struct import pack  from sys import byteorder  import copy  import pyaudio  import wave    THRESHOLD = 500  # audio levels not normalised.  CHUNK_SIZE = 1024  SILENT_CHUNKS = 3 * 44100 / 1024  # about 3sec  FORMAT = pyaudio.paInt16  FRAME_MAX_VALUE = 2 ** 15 - 1  NORMALIZE_MINUS_ONE_dB = 10 ** (-1.0 / 20)  RATE = 44100  CHANNELS = 1  TRIM_APPEND = RATE / 4    def is_silent(data_chunk):      """Returns 'True' if below the 'silent' threshold"""      return max(data_chunk) < THRESHOLD    def normalize(data_all):      """Amplify the volume out to max -1dB"""      # MAXIMUM = 16384      normalize_factor = (float(NORMALIZE_MINUS_ONE_dB * FRAME_MAX_VALUE)                          / max(abs(i) for i in data_all))        r = array('h')      for i in data_all:          r.append(int(i * normalize_factor))      return r    def trim(data_all):      _from = 0      _to = len(data_all) - 1      for i, b in enumerate(data_all):          if abs(b) > THRESHOLD:              _from = max(0, i - TRIM_APPEND)              break        for i, b in enumerate(reversed(data_all)):          if abs(b) > THRESHOLD:              _to = min(len(data_all) - 1, len(data_all) - 1 - i + TRIM_APPEND)              break        return copy.deepcopy(data_all[_from:(_to + 1)])    def record():      """Record a word or words from the microphone and       return the data as an array of signed shorts."""        p = pyaudio.PyAudio()      stream = p.open(format=FORMAT, channels=CHANNELS, rate=RATE, input=True, output=True, frames_per_buffer=CHUNK_SIZE)        silent_chunks = 0      audio_started = False      data_all = array('h')        while True:          # little endian, signed short          data_chunk = array('h', stream.read(CHUNK_SIZE))          if byteorder == 'big':              data_chunk.byteswap()          data_all.extend(data_chunk)            silent = is_silent(data_chunk)            if audio_started:              if silent:                  silent_chunks += 1                  if silent_chunks > SILENT_CHUNKS:                      break              else:                   silent_chunks = 0          elif not silent:              audio_started = True                      sample_width = p.get_sample_size(FORMAT)      stream.stop_stream()      stream.close()      p.terminate()        data_all = trim(data_all)  # we trim before normalize as threshhold applies to un-normalized wave (as well as is_silent() function)      data_all = normalize(data_all)      return sample_width, data_all    def record_to_file(path):      "Records from the microphone and outputs the resulting data to 'path'"      sample_width, data = record()      data = pack('<' + ('h' * len(data)), *data)        wave_file = wave.open(path, 'wb')      wave_file.setnchannels(CHANNELS)      wave_file.setsampwidth(sample_width)      wave_file.setframerate(RATE)      wave_file.writeframes(data)      wave_file.close()    if __name__ == '__main__':      print("Wait in silence to begin recording; wait in silence to terminate")      record_to_file('demo.wav')      print("done - result written to demo.wav")  


Solution:4

The pyaudio website has many examples that are pretty short and clear: http://people.csail.mit.edu/hubert/pyaudio/


Solution:5

import pyaudio  import wave  from array import array    FORMAT=pyaudio.paInt16  CHANNELS=2  RATE=44100  CHUNK=1024  RECORD_SECONDS=15  FILE_NAME="RECORDING.wav"    audio=pyaudio.PyAudio() #instantiate the pyaudio    #recording prerequisites  stream=audio.open(format=FORMAT,channels=CHANNELS,                     rate=RATE,                    input=True,                    frames_per_buffer=CHUNK)    #starting recording  frames=[]    for i in range(0,int(RATE/CHUNK*RECORD_SECONDS)):      data=stream.read(CHUNK)      data_chunk=array('h',data)      vol=max(data_chunk)      if(vol>=500):          print("something said")          frames.append(data)      else:          print("nothing")      print("\n")      





        
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