by Richard S. Burwen
Have you ever listened to a trumpet outdoors, with its bell pointed at your ears?  That is flat response with no sound reflections.  It sounds awful.

To make the trumpet enjoyable, listen to it in a reasonably live acoustic space, at an angle of 45 degrees or so off its axis.  Multiple sound reflections
from the surfaces of the room (preferably non-parallel) add and subtract at various frequencies via comb filtering to produce hundreds or thousands of
resonant ripples in the frequency response.  That is what makes instruments sound musical.

The multiple resonances make it harder to hear noises and other imperfections in the trumpet sound.

What is missing in a real room is and artificial reverberation systems is significant sound reflections higher than 5 kHz.  That is where Burwen patent
pending high frequency reverberation comes in.  It does for high frequency imperfections in recorded sound what lower frequency reflections do for the

The trick is to get thousands of small ripples in the frequency response without getting a few whoppers that bother you.

Automatic equalizers use microphone measurements to reduce the biggest resonances, generally below 500 Hz, so the average bass response is flatter.  
What you do not want is a system so sensitive that it attempts to remove reverberation.  That cannot be done anywhere other than at the microphone
location and is likely to degrade the sound where you listen.  While this type of equalizer is of some help, it can balance the overall tone quality of a
speaker and room only to within 4 dB or so of optimum.

What you ear thinks of as tonal balance is the general trend of the frequency response curve, amongst all the ripples.  For poorly balanced sound, 1 or 2
dB change in the frequency response curve is difficult to hear.  I used to think 0.5 dB change at middle frequencies was all I could hear.  Not so.  Once
the sound is nearly perfectly balanced, as little 0.1 dB tilt in the frequency response becomes significant.

For example, I remastered one of my own most favorite live classical concert recordings 7 times using
AUDIO SPLENDOR, each time making some
improvement in the sound.  The final frequency response curve has 15 dB boost at 15 Hz and 3 dB attenuation at 5 kHz.  As I reached "perfection" I spent
the last 15 minutes deciding on a 0.1 dB increase in the 3 kHz slider.  Without it the orchestra was more natural.  With it the cymbals were more natural.

All the tone sliders in the BURWEN BOBCAT TONE BALANCER  produce gradual changes in frequency response in fine steps of 0.1 dB.  The LOW, MID
HIGH, and HIGH sliders, which each have a +/- 30 dB range are 601 position switches.  BASS, MIDDLE, and TREBLE are 401 position switches
covering +/- 20 dB.   

How did you pick your speaker system?  Probably you thought it had very well balanced sound on program material you considered to be a reference.  In
assessing tonal balance your ear averaged out ripples in frequency response caused by room reflections and speaker imperfections.

How close can the average tonal balance of your speaker system be to what you would consider to be best tonal balance on your reference program?  If
you paid $100,000, maybe +/-2 dB in the frequency range from 100 Hz to 5,000 Hz.  You need high resolution tone controls to bring it within tenths of a

In rare instances it is possible make it seem as though one or a few players are in your own listening room.  For most recordings the best that can be
done is to try to transport you to the original recording environment or a different hall.  Two parts of the audio range have a big effect on your perception
of closeness - middles around 800 Hz and extreme high frequencies above 5 kHz.

Pushing both MIDDLE and TREBLE sliders down can help vocals by humping up the 1 kHz region and placing a small dip at 3300 Hz where screech
occurs and your ear is most sensitive.  A peak of only 1 to 2 dB may be all you need, produced by setting both MIDDLE and TREBLE at -3 to -4 dB.

Pushing the MID HIGH and/or HIGH controls up a few dB will clarify words and increase sibilance.  Often I like pushing MID HIGH down and HIGH up to
keep the sound from getting too thin.

The choice of high frequency reverberation also affects presence.  For vocals I use either BASIC which is most natural or RECITAL which provides more
ambiance, hinting of a small hall, and seems more exciting.  Clicking RVRB OFF highlights the artificial reverberation in the recording itself and it may be

When you move any slider, the BURWEN BOBCAT TONE BALANCER automatically adjusts the listening volume in attempt to make it psychologically the
same, but the compensation is not perfect.  So in judging presence you may want to readjust the volume slightly.  Louder sounds closer.  Often the louder
of two sounds seems superior even when it is inferior.

Pushing LOW up can boost 15 Hz as much as 30 dB and may be able to extend the bass response of your speaker an octave lower.  Beyond a certain
point the bass becomes boomy, but this can be alleviated by pushing the BASS slider down.  How much boost you can use depends upon the low
frequency content of the recording, the power capability of your amplifier-speaker combination, and your listening volume.  A resonant rise at the low
corner frequency of your speaker cannot be perfectly compensated the way an automatic equalizer can reduce a resonance, but the effect can be
pleasing.  An efficient speaker fed by a high damping factor semiconductor amplifier will usually have a smaller resonant peak at its low corner frequency
and will be more accurately compensated by the BURWEN BOBCAT TONE BALANCER.

All 3 reverberation selections are designed to spread the stereo image a little wider than the speakers.  Whether this actually occurs depends very much
on the tone slider settings.  Boosting high frequency content via the MID HIGH and/or the HIGH slider widens the stereo image beyond the speakers.   
Attenuating the high frequencies or boosting the middle frequencies will narrow the stereo image.  Boosting middle frequencies and extreme high
frequencies at the same time can increase presence while maintaining a normal or very slightly widened stereo image.

The stereo image width can also be controlled by mixing.  Use the INPUT CH - SPKRS 43 position mix selector to deliberately widen or narrow the stereo
image.  Widening is accomplished by slightly blending the left and right channels out of phase.  Normally this is done when a front center speaker is used
because it tends to narrow the stereo image.  Use 2 - ALL, 2 WIDER - ALL, or 2 WIDE - ALL for 3 progressively higher degrees of widening,
accomplished by varying the level of blending.

To narrow the stereo image and bring a vocalist closer, the PHONE + ALL mix does the opposite.  It slightly blends the left and right channels in-phase.  
Stereo recordings heard via headphones are too wide.  This mix restores normal width.  FL + FR - ALL provides extreme in-phase blending to
monophonic sound.

Some extremely bad recordings can be surprisingly improved by drastic measures.  That is why the tone sliders have such huge dB ranges that can add
up to more than 70 dB boost or cut at 15 Hz and 20 kHz.  The greatest amount of bass boost I ever used was 68 dB on a laser disc containing the movie
La Traviata.  The low bass had been cut off but there was a trace of it left that could retrieved via the huge bass boost.  Some very rough, raspy voice
recordings can become tolerable by attenuating the high frequencies as much as 40 dB.