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#!/usr/bin/env bash
# bash 4.1.5(1) Linux Ubuntu 10.04 Date : 2011-09-11
#
# _______________| noise : ambient Brown noise generator (cf. white noise).
#
# Usage: noise [minutes=59] [band-pass freq center=1786] [wave]
# ^minutes can be any non-zero integer.
#
# Dependencies: play (from sox package)
# Brownian noise, also known as Brown noise or red noise, is the kind of signal
# noise produced by Brownian motion, hence its alternative name of random walk
# noise. The term "Brown noise" does not originate from the color, but from
# Robert Brown who discovered Brownian motion. Brown noise is produced by
# integrating white noise. The sound is a low roar resembling a waterfall or
# heavy rainfall. We shall filter it through a band-pass, then add effects
# to mellow the output for ambience.
# [/] - could increase volume oscillation (amplitude modulation) to simulate
# waves or breathing pattern -- but this could be too relaxing.
# Hear the free online services listed at the end of file.
# Our goal here is calm concentration in a noisy environment.
# CHANGE LOG Code posted at https://gist.github.com/1209835
#
# 2011-09-11 Repeat use of one-minute segment to cut CPU usage by 95%.
# Fix tremolo to give very slow wave oscillation in volume.
# (Thanks to xguse for his gist at github.)
# Constant volume introduces tension psychologically.
# 2011-09-10 First version based on 2009 article by Tom Swiss, and
# subsequent comments. See below for relevant portions.
# _____ Prelims
set -u
# ^ unbound (i.e. unassigned) variables shall be errors.
# Example of default assignment: arg1=${1:-'foo'}
set -e
# ^ error checking :: Highly Recommended (caveat: you can't check $? later).
#
# _______________ :: BEGIN Script ::::::::::::::::::::::::::::::::::::::::
minutes=${1:-'59'}
repeats=$(( minutes - 1 ))
center=${2:-'1786'}
wave=${3:-'0.02'}
# ^increase for more volume oscillation, but suggest no higher than 0.20
noise='brown'
# ^your choice: 'white', 'pink', 'brown', 'tpdf'
# where tpdf stands for Triangular Probability Density Function (cf. dither).
# N.B. - white and pink noise have higher frequencies than Brown.
len='01:00'
# ^CONSTANT one minute. (Format for specifying time length is hh:mm:ss.frac)
# ___ATTN___ We first pre-compute one minute of audio output to file,
# then playback repeatedly as necessary to satisfy minutes argument.
# This dramatically cuts CPU usage by 95% after the first minute.
echo " :: Please stand-by... sox will 'play' $noise noise for $minutes minutes."
play --no-show-progress -c 2 --null synth $len ${noise}noise band -n $center 499 \
tremolo $wave 37 reverb 19 repeat $repeats
# # Previously published one-line versions misused tremolo:
# play -c 2 --null synth $len brownnoise band -n 1800 1400 tremolo 500 .1 reverb 50
# play -c 2 --null synth $len brownnoise band -n 2500 4000 tremolo 20 .1 reverb 50
# play --null synth $len brownnoise band -n 1200 200 tremolo 20 .1 reverb 20
# play --null synth $len brownnoise band -n 1200 200 tremolo 20 .1
# _____ ARGUMENTS explained via "man sox"
# -q, --no-show-progress
# Run in quiet mode when SoX wouldn't otherwise do so; this is
# the opposite of the -S option.
#
# -S, --show-progress
# Display input file format/header information, and processing
# progress as input file(s) percentage complete, elapsed time,
# and remaining time (if known; shown in brackets), and the
# number of samples written to the output file. Also shown is a
# peak-level meter, and an indication if clipping has occurred.
# -c 2
# Two channels. Without this, the output is not stereo.
# -n, --null
# This can be used in place of an input or output filename to
# specify that a `null file' is to be used. Note that here,
# `null file' refers to a SoX-specific mechanism and is not
# related to any operating-system mechanism with a similar name.
# Using a null file to input audio is equivalent to using a
# normal audio file that contains an infinite amount of silence,
# and as such is not generally useful unless used with an effect
# that specifies a finite time length (such as trim or synth).
# synth
# Some noise options: whitenoise, tpdfnoise, pinknoise, brownnoise.
# band [-n] center[k] [width[h|k|o|q]]
# Apply a band-pass filter. The frequency response drops
# logarithmically around the center frequency. The width
# parameter gives the slope of the drop. The frequencies at
# center + width and center - width will be half of their
# original amplitudes. band defaults to a mode oriented to
# pitched audio, i.e. voice, singing, or instrumental music.
# The -n (for noise) option uses the alternate mode for un-
# pitched audio (e.g. percussion). Warning: -n introduces a
# power-gain of about 11dB in the filter, so beware of output
# clipping. band introduces noise in the shape of the filter,
# i.e. peaking at the center frequency and settling around it
#
# Consider this for centering the band-pass...
#
# Freq (Hz) Octave Description
# 16 to 32 1st Human threshold, the lowest pedal notes
# of a pipe organ.
# 32 to 512 2nd to 5th Rhythm frequencies, where the lower and upper
# bass notes lie.
# 512 to 2048 6th to 7th Defines human speech intelligibility, gives a
# horn-like or tinny quality to sound.
# 2048 to 8192 8th to 9th Gives presence to speech, where labial and
# fricative sounds lie.
# 8192 to 16384 10th Brilliance, the sounds of bells and the ringing
# of cymbals. In speech, the sound of
# the letter "S" (8000-11000 Hz)
# Source: http://en.wikipedia.org/wiki/Audio_frequency
#
# Avoid the really low frequencies which will produce disturbing rumble.
# tremolo speed [depth]
# Apply a tremolo (low frequency amplitude modulation) effect to
# the audio. The tremolo frequency in Hz is given by speed, and
# the depth as a percentage by depth (default 40). Increasing
# the depth gives wider range between soft and loud volumes.
# reverb [-w|--wet-only] [reverberance (50%) [HF-damping (50%)
# [room-scale (100%) [stereo-depth (100%)
# [pre-delay (0ms) [wet-gain (0dB)]]]]]]
# repeat count
# Repeat the entire audio count times. Requires temporary file
# space to store the audio to be repeated. [But where exactly?]
# _______________ "white noise" generator with sox [edited for code content]
# by Tom Swiss, http://unreasonable.org/node/303
# January 2007, updated circa September 2009,
# included comments through September 2011
#
# Sox is "the Swiss army knife of sound processing programs." It includes sound
# generation capabilties for pure tones and white noise. "Pink noise" is
# also in sox's bag of tricks. After a bit of experimentation, I found the
# following shell script produced agreeable results:
#
# len='7:00:00'
# play -t sl - synth $len pinknoise band -n 1200 200 tremolo 20 .1 < /dev/zero
#
# __________ Comments
#
# Drew Haven: This beats the heck out of "cat /dev/urandom > /dev/dsp". The band
# filter is nice to take out the pops.
#
# gi1242: With recent versions of sox, things are a little simpler:
# play -n synth 60:00 brownnoise
# produces brown noise for an hour. (Replace brown with pink/white if you
# prefer. My baby sleeps best with brown).
#
# Tom Swiss: "Brown" in "brown noise" means Brownian motion. It's also called
# red noise. I learned something today, hooray!
#
# Adrien Beau, 30 January 2011: You can replace the "-t sl -" and "< /dev/zero"
# parts with the "-n" option, so your sox invocation becomes:
# ^= --null (for null file)
# play -n synth $len pinknoise band -n 1200 200 tremolo 20 .1
# The brown noise sounds the best in my opinion.
#
# Dennis Murczak, 5 May 2011: I adapted the line to a "my neighbor is having a
# party and I need to study" situation:
# play -c 2 -n synth pinknoise band -n 2500 4000 reverb 20
# The band pass is centered on human voice frequencies and wide enough to also
# cover most of the musical frequency range, without producing annoying
# high-pitched noise. The slight reverb adds a background/ambient quality for
# less distraction.
exit 0
# _______________ EOS :: END of Script ::::::::::::::::::::::::::::::::::::::::
# _____ Free ONLINE alternatives
#
# Simply Noise for white, pink and brown/red noise generator; uses Flash:
# http://simplynoise.com $0.99 app available
# [Flash consumes about 30 times more than our script in CPU usage!]
#
# PlayNoise for white, pink, and brown noise generator; uses Javascript/HTML5:
# http://playnoise.com
# _____ References
# Re: Brown noise, see http://en.wikipedia.org/wiki/Brownian_noise
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