filter diagram

filter.py

#!/usr/bin/env python

from __future__ import division
import sys
import math

OVERSAMPLING_FACTOR = 1
SAMPLING_FREQUENCY = 48000 * OVERSAMPLING_FACTOR
PASSES = 100000

F = 1000.0
MINF = F / 1.1
MAXF = F * 1.1

Q = 1.0 / (1.0 + F / SAMPLING_FREQUENCY * (math.pi * 2.0))
P = 1.0 - Q

R = 0.25
MINR = R - 0.03
MAXR = R + 0.03

NUMX = 80
NUMY = 23

MAXX = NUMX - 1
MAXY = NUMY - 1

MINL = math.log(MINF)
MAXL = math.log(MAXF)

grid = []
for i in range(NUMY):
    grid.append([' '] * NUMX)

def dump():
    sys.stdout.write("\x1B[H")
    for row in grid:
        for char in row:
            sys.stdout.write(char)
        print

sys.stdout.write("\x1B[H\x1B[J")
for x in range(NUMX):
    f = math.exp((x / MAXX) * (MAXL - MINL) + MINL)
    ratio = f / SAMPLING_FREQUENCY * (math.pi * 2.0)

    squaresum = 0.0
    squaresum2 = 0.0
    filtered = 0.0
    complementary = 0.0
    for i in range(PASSES):
        v = (math.cos((i - 0.5) * ratio) - math.cos((i + 0.5) * ratio)) / ratio
        filtered = v * P + filtered * Q
        complementary = v - filtered
        squaresum += filtered * filtered
        squaresum2 += complementary * complementary

    r = squaresum / PASSES
    y = int(round((r - MAXR) / (MINR - MAXR) * MAXY))
    if 0 <= y < NUMY:
        grid[y][x] = '+'

    r = squaresum2 / PASSES
    y = int(round((r - MAXR) / (MINR - MAXR) * MAXY))
    if 0 <= y < NUMY:
        grid[y][x] = '*'

    dump()