Detect tap with pyaudio from live mic

One way I've done it:

• read a block of samples at a time,say 0.05 seconds worth
• compute theRMS amplitude of the block (squareroot of the average of the squares ofthe individual samples)
• if the block's RMS amplitude is greater than a threshold, it's a "noisy block" else it's a "quiet block"
• a sudden tap would be a quiet block followed by a small number of noisy blocks followed by a quiet block
• if you never get a quiet block, your threshold is too low
• if you never get a noisy block, your threshold is too high

My application was recording "interesting" noises unattended, so it would record as long as there were noisy blocks. It would multiply the threshold by 1.1 if there was a 15-second noisy period ("covering its ears") and multiply the threshold by 0.9 if there was a 15-minute quiet period ("listening harder"). Your application will have different needs.

Also, just noticed some comments in my code regarding observed RMS values. On the built in mic on a Macbook Pro, with +/- 1.0 normalized audio data range, with input volume set to max, some data points:

• 0.003-0.006 (-50dB to -44dB) an obnoxiously loud central heating fan in my house
• 0.010-0.40 (-40dB to -8dB) typing on the same laptop
• 0.10 (-20dB) snapping fingers softly at 1' distance
• 0.60 (-4.4dB) snapping fingers loudly at 1'

Update: here's a sample to get you started.

#!/usr/bin/python# open a microphone in pyAudio and listen for tapsimport pyaudioimport structimport mathINITIAL_TAP_THRESHOLD = 0.010FORMAT = pyaudio.paInt16 SHORT_NORMALIZE = (1.0/32768.0)CHANNELS = 2RATE = 44100  INPUT_BLOCK_TIME = 0.05INPUT_FRAMES_PER_BLOCK = int(RATE*INPUT_BLOCK_TIME)# if we get this many noisy blocks in a row, increase the thresholdOVERSENSITIVE = 15.0/INPUT_BLOCK_TIME                    # if we get this many quiet blocks in a row, decrease the thresholdUNDERSENSITIVE = 120.0/INPUT_BLOCK_TIME # if the noise was longer than this many blocks, it's not a 'tap'MAX_TAP_BLOCKS = 0.15/INPUT_BLOCK_TIMEdef get_rms( block ):    # RMS amplitude is defined as the square root of the     # mean over time of the square of the amplitude.    # so we need to convert this string of bytes into     # a string of 16-bit samples...    # we will get one short out for each     # two chars in the string.    count = len(block)/2    format = "%dh"%(count)    shorts = struct.unpack( format, block )    # iterate over the block.    sum_squares = 0.0    for sample in shorts:        # sample is a signed short in +/- 32768.         # normalize it to 1.0        n = sample * SHORT_NORMALIZE        sum_squares += n*n    return math.sqrt( sum_squares / count )class TapTester(object):    def __init__(self):        self.pa = pyaudio.PyAudio()        self.stream = self.open_mic_stream()        self.tap_threshold = INITIAL_TAP_THRESHOLD        self.noisycount = MAX_TAP_BLOCKS+1         self.quietcount = 0         self.errorcount = 0    def stop(self):        self.stream.close()    def find_input_device(self):        device_index = None                    for i in range( self.pa.get_device_count() ):                 devinfo = self.pa.get_device_info_by_index(i)               print( "Device %d: %s"%(i,devinfo["name"]) )            for keyword in ["mic","input"]:                if keyword in devinfo["name"].lower():                    print( "Found an input: device %d - %s"%(i,devinfo["name"]) )                    device_index = i                    return device_index        if device_index == None:            print( "No preferred input found; using default input device." )        return device_index    def open_mic_stream( self ):        device_index = self.find_input_device()        stream = self.pa.open(   format = FORMAT,                                 channels = CHANNELS,                                 rate = RATE,                                 input = True,                                 input_device_index = device_index,                                 frames_per_buffer = INPUT_FRAMES_PER_BLOCK)        return stream    def tapDetected(self):        print("Tap!")    def listen(self):        try:            block = self.stream.read(INPUT_FRAMES_PER_BLOCK)        except IOError as e:            # dammit.             self.errorcount += 1            print( "(%d) Error recording: %s"%(self.errorcount,e) )            self.noisycount = 1            return        amplitude = get_rms( block )        if amplitude > self.tap_threshold:            # noisy block            self.quietcount = 0            self.noisycount += 1            if self.noisycount > OVERSENSITIVE:                # turn down the sensitivity                self.tap_threshold *= 1.1        else:                        # quiet block.            if 1 <= self.noisycount <= MAX_TAP_BLOCKS:                self.tapDetected()            self.noisycount = 0            self.quietcount += 1            if self.quietcount > UNDERSENSITIVE:                # turn up the sensitivity                self.tap_threshold *= 0.9if __name__ == "__main__":    tt = TapTester()    for i in range(1000):        tt.listen()

a simplified version of the above code...

import pyaudioimport structimport mathINITIAL_TAP_THRESHOLD = 0.010FORMAT = pyaudio.paInt16 SHORT_NORMALIZE = (1.0/32768.0)CHANNELS = 2RATE = 44100  INPUT_BLOCK_TIME = 0.05INPUT_FRAMES_PER_BLOCK = int(RATE*INPUT_BLOCK_TIME)OVERSENSITIVE = 15.0/INPUT_BLOCK_TIME                    UNDERSENSITIVE = 120.0/INPUT_BLOCK_TIME # if we get this many quiet blocks in a row, decrease the thresholdMAX_TAP_BLOCKS = 0.15/INPUT_BLOCK_TIME # if the noise was longer than this many blocks, it's not a 'tap'def get_rms(block):    # RMS amplitude is defined as the square root of the     # mean over time of the square of the amplitude.    # so we need to convert this string of bytes into     # a string of 16-bit samples...    # we will get one short out for each     # two chars in the string.    count = len(block)/2    format = "%dh"%(count)    shorts = struct.unpack( format, block )    # iterate over the block.    sum_squares = 0.0    for sample in shorts:    # sample is a signed short in +/- 32768.     # normalize it to 1.0        n = sample * SHORT_NORMALIZE        sum_squares += n*n    return math.sqrt( sum_squares / count )pa = pyaudio.PyAudio()                                 #]                                                       #|stream = pa.open(format = FORMAT,                      #|         channels = CHANNELS,                          #|---- You always use this in pyaudio...         rate = RATE,                                  #|         input = True,                                 #|         frames_per_buffer = INPUT_FRAMES_PER_BLOCK)   #]tap_threshold = INITIAL_TAP_THRESHOLD                  #]noisycount = MAX_TAP_BLOCKS+1                          #|---- Variables for noise detector...quietcount = 0                                         #|errorcount = 0                                         #]         for i in range(1000):    try:                                                    #]        block = stream.read(INPUT_FRAMES_PER_BLOCK)         #|    except IOError, e:                                      #|---- just in case there is an error!        errorcount += 1                                     #|        print( "(%d) Error recording: %s"%(errorcount,e) )  #|        noisycount = 1                                      #]    amplitude = get_rms(block)    if amplitude > tap_threshold: # if its to loud...        quietcount = 0        noisycount += 1        if noisycount > OVERSENSITIVE:            tap_threshold *= 1.1 # turn down the sensitivity    else: # if its to quiet...        if 1 <= noisycount <= MAX_TAP_BLOCKS:            print 'tap!'        noisycount = 0        quietcount += 1        if quietcount > UNDERSENSITIVE:            tap_threshold *= 0.9 # turn up the sensitivity