Realtime waveform display with tunable trigger level

scope_with_trigger.py

#! /usr/bin/env python3
# -*- coding: utf-8 -*-
__author__ = 'Scott H. Hawley'
__copyright__ = 'Scott H. Hawley'
__license__ = "MIT Licence (do what you want, don't blame me)"

import numpy as np
import cv2
import soundcard as sc  # https://github.com/bastibe/SoundCard
from scipy.ndimage.interpolation import shift

# screen size & related variables
imWidth, imHeight = 1024, 512
y0 = imHeight/2                # horizontal axis
draw_amp = imHeight/2-1        # maximum amplitude in pixels


def draw_wave(screen, mono_audio, xs, title="oscilloscope", gain=5):
    screen *= 0                                    # clear the screen
    # next line determines the y-values for the wave form. - sign because CG is upside down
    ys = ( y0 - draw_amp * np.clip( gain * mono_audio[0:len(xs)], -1, 1) ).astype(np.int)
    pts = np.array(list(zip(xs,ys)))               # pair up xs & ys
    cv2.polylines(screen,[pts],False,(0,255,0))    # draw lines connecting the points
    cv2.imshow(title, screen)                      # show what we've got
    return

def find_trigger(mono_audio, thresh=0.02, pos_slope=True):  # thresh = trigger level
    start_ind = None     # this is where in the buffer the trigger should go; None
    shift_forward = shift(mono_audio, 1, cval=0)
    if pos_slope:
        inds = np.where(np.logical_and(mono_audio >= thresh, shift_forward <= thresh))
    else:
        inds = np.where(np.logical_and(mono_audio <= thresh, shift_forward >= thresh))
    if (len(inds[0]) > 0):
        start_ind = inds[0][0]
    return start_ind

# main routine; audio buffer & sample rate
def oscilloscope(buf_size=1024, fs=44100):
    default_mic = sc.default_microphone()
    print("oscilloscope: listening on ",default_mic)
    gain, trig_level = 5, 0.02   # seems to work on my mac

    # allocate storage for 'screen'
    screen = np.zeros((imHeight,imWidth,3), dtype=np.uint8) # 3=color channels
    xs = np.arange(imWidth).astype(np.int)                  # x values of pixels
    while (1):                             # keep looping until someone stops this
        with default_mic.recorder(samplerate=fs) as mic:
            audio_data = mic.record(numframes=buf_size)  # get some audio from the mic
        bgn = find_trigger(audio_data[:,0], thresh=trig_level)
        if bgn is not None:                                  # try to trigger
            end = min(bgn+imWidth, buf_size)                 # don't go off the end of the buffer
            pad_len = max(0, imWidth - (end-bgn) )           # might have to pad with zeros
            draw_wave(screen, np.pad(audio_data[bgn:end,0],(0,pad_len), \
                    'constant',constant_values=0), xs, gain=gain)             # draw left channel
        else:
            draw_wave(screen, audio_data[0:imWidth,0]*0, xs, gain=gain)   # draw zero line

        key = cv2.waitKey(1) & 0xFF    # keyboard input
        if ord('q') == key:       # quit key
            break
        elif ord('=') == key:     # = sign  (couldn't get arrow keys to register!)
            trig_level += 0.002
            print("trig_level =",trig_level)
        elif ord("'") == key:     # single quote
            trig_level -= 0.002
            print("trig_level =",trig_level)
        elif ord('[') == key:      # left bracket
            gain *= 0.9
            print("gain =",gain)
        elif ord(']') == key:      # right bracket
            gain += 1.1
            print("gain =",gain)
    return

if __name__ == '__main__':
    oscilloscope(buf_size=int(imWidth*1.5))   # give the buffer a little extra room so you don't see zero-pads