		BINAURAL BEAT BIOFEEDBACK FROM EEG
			by Philip Soden

DISCLAIMER
In using these files you agree that the author is not responsible for 
any injury to persons or property arising from such use.  The files 
may be distributed freely on condition that this readme.txt file is 
included in the distribution.  The files may not be sold or otherwise 
used for profit-making purposes without the written consent of the 
author.


HAZARD WARNING
Listening to binaural beat tones can produce altered states of 
consciousness and is reported to have triggered epileptic seizures. 
This application should not be used when driving or operating 
machinery, and should not be used by epileptics or by anyone 
receiving psychiatric treatment.


CONTENTS
This zip file (SB16BEAT.ZIP) contains the following:

SB16BEAT.CFG	
A Waverider configuration file to generate a MIDI output from one 
channel of EEG, the output note varying with the average EEG 
frequency.

SB16BEAT.XLS
An Excel spreadsheet for calculating output frequencies of 
left and right channels, delta f (binaural beat) for a range of MIDI 
notes, and the effect of note range selection (in Waverider) on the
offset between measured EEG and fed-back binaural beat frequencies.

README.TXT
This text file.


HARDWARE / SOFTWARE REQUIREMENTS

To create binaural beat biofeedback from EEG, this setup needs a 
Waverider or Waverider Jr. and Waveware software to amplify and process the
EEG signals, a SoundBlaster SB16 or compatible card, plus a PC / compatible,
with Microsoft Windows or Windows 95.

If you don't have a Waverider, you can skip the bio-feedback and still 
make binaural beat tones by using a MIDI sequencer / composition 
software to play a selected sequence of notes on the SB16's FM MIDI synthesizer.


SETUP

Unzip the file and copy sb16beat.cfg to the c:\waveware\ 
directory.
  
Start Waverider and select Load Configuration from the Files pull-
down menu. Select sb16beat.cfg, gel up the headband and you're ready 
to go.


HOW IT WORKS

The Waverider amplifies and processes EEG signals from electrodes on 
the Waverider headband, and the Waveware software produces a MIDI output
which controls the sound card from the EEG inputs. With the sb16beat.cfg
file loaded into Waverider, the output MIDI notes vary in pitch in
proportion to the average brainwave frequency.
 
When a "note-on" signal is received from the Waverider, the SoundBlaster
plays two MIDI instruments a semitone apart, one in each ear (headphones
are recommended for effective binaural beat listening). The instruments
are identical in every respect except their note range. One is set to the
range 20 - 60, the other to the range 21 - 61. This produces a semitone
offset between the instruments irrespective of variations in the input
parameters. 

One instrument is assigned to MIDI channel 1, the other is in MIDI
channel 2 to permit separate pan positioning of each
instrument. The panning is achieved by two additional WaveRider MIDI windows
selected to output to Controller 10 (pan position). One is set on MIDI
Channel 1 and its output range is set to 0 - 0, i.e. panned left
irrespective of input variations. The other control window outputs to MIDI
channel 2 and its output range is set to 127 - 127, i.e. panned right
irrespective of input variations.

As the average EEG frequency reduces, WaveRider plays lower MIDI notes on
both instruments, which has the effect of reducing the frequency difference
(beat) between the left and right signals.  If higher notes are played,
the frequency of the tones and also the beat frequency between them are
increased.

This gives useful conscious audible feedback in that the notes 
themselves follow the average EEG frequency up and down.  More to 
the point, the beat frequency between the two tones also reduces and 
increases, tracking the average EEG frequency.  

The theory of binaural beat stimulation is that brainwaves tend to 
follow the applied beat frequency (if the offset between EEG and
beat frequency is less than 15%), so by choosing a binaural beat
frequency that stays slightly below the average EEG frequency, it 
is possible to lead the EEG slower into alpha and theta states via this 
bio-feedback mechanism.


ADJUSTING PITCH AND OFFSET

The offset frequency (i.e. the difference between the average EEG 
frequency and the binaural beat frequency) can be adjusted, and can  
be set to lead the brainwaves up or down in frequency.  This is achieved
by adjusting the output note ranges for the two MIDI instruments within
Waverider.

Open sb16beat.xls (Microsoft Excel spreadsheet) to find the note range
combination that produces your desired offset. 

If you want to change the offset, enter another combination of start and 
end notes in sb16beat.xls until you reach the desired offset, and enter
those values in Waverider (double click on the Waverider MIDI display
windows to access this function). NB you must change the note range
in both instruments, maintaining the one note offset between the ranges.

Please note that negative offset values represent beat frequencies 
that are higher than the average EEG frequency, i.e. they would tend
to lead the brainwaves upwards into beta.  

Unfortunately the SB16's MIDI synthesizer is less than ideal for binaural
beats in two respects:

1. This setup operates at very low note frequencies (40-100Hz) and
the higher frequency digital noises produced by the SB16 are audible
above the low notes. The chirps and whistles can get a bit annoying -
they're not exactly conducive to meditative repose.

2. There are only a few instruments amongst those available in the SB16's
FM synth that don't drive you nuts after prolonged listening to the
somewhat discordant playing of notes separated by a semitone.

Ideally what is needed is an instrument that has few harmonics and a slow
attack/decay to move from one note to the next as smoothly as possible.
The humble Ocarina seems to fit the bill, but experimenters
might also try Synth Pad 2, Pad 5 or Pad 7 for a bit of variation
(MIDI instrument numbers 89, 92 and 94 respectively).




Philip Soden
dven@mail.hkapa.edu
November 1996

   
