Python Sonar

#!/usr/bin/env python2.7

# In order to run this you will need python-numpy and alsa-utils to be installed
# I'm sorry for this being quick and dirty

from sys import stdin, argv
from struct import unpack, pack, Struct
import subprocess as sp
import numpy as npy
import time

rate = 16000
nsamples = 100
nchars = 75
block = 2000
ssize = 2
sformat = "S16_LE"
sendian = "<"
schar = "h"
ssingle = sendian + schar
maxval = (2**14-1)*2+1
minval = -maxval

blockformat = sendian + schar * block

packer = Struct(blockformat)
up = packer.unpack
pa = packer.pack

spack = Struct(sendian+schar)

zeroblock = spack.pack(0)*(block*ssize)
tickblock = (
    spack.pack(0) +
    spack.pack(minval) +
    spack.pack(0) +
    spack.pack(maxval) +
    spack.pack(0)*((block-2)*2))
params = [
    "-f", sformat,
    "-r", str(rate),
    "-t", "raw",
    ]
pin = sp.Popen(
    ["arecord", "-c", "1"] + params,
    stdout=sp.PIPE
    )
pout = sp.Popen(
    ["aplay", "-c", "2"] + params,
    stdin=sp.PIPE
    )
calib = None
while True:
    pout.stdin.write(tickblock)
    inp = pin.stdout.read(block*ssize)
    if (len(inp) < block*ssize):
        print "Block discarded, too short"
        break
    inpa = npy.array(packer.unpack(inp))
    inpa = inpa[:-1]-inpa[1:]
    peakt = npy.argmax(inpa)
    if peakt > 100:
        pin.stdout.read(ssize*((peakt-100)/100+1))
    elif peakt < 100:
        pout.stdin.write(zeroblock[:ssize*2])
    part = inpa[peakt:peakt+nsamples]
    if len(part) < nsamples:
        continue
    if calib == None:
        calib = part
        continue
    swap = part
    part = abs(part-calib)
    tmp = [" "]*nchars
    detected = False
    for i in xrange(len(part)):
        threshold = 10+((nsamples-i)*130/nsamples)
        if part[i] > threshold:
            if i > 2:
                detected = True
            tmp[(i*nchars)/nsamples] = "#"
        elif detected:
            tmp[(i*nchars)/nsamples] = "-"
    if detected:
        print "".join(tmp)
        calib = swap