MAKE FRIENDS WITH YOUR AMP - Gollihur Music

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High Pass Filter – aka Low (Bass, Sub-Bass) Cut Filter, Subsonic Filter, Depth Control – The counterintuitively
named “High Pass” Filter is so-called because it lets high frequencies pass. And, like the
black knight, it stops undesirables (in this case, boomy and muddy low frequencies) from passing,
starting at the frequency where you adjust the knob or slider. This feature is a popular and very
useful one, particularly for upright bass players, as it can get rid of low frequency rumble, and kill
tone-robbing subsonic sounds beneath the range of notes your bass can play.
While we know a low E is 41.2Hz and a low B is 30Hz, it’s best to set this control by ear, because it isn’t a sharp
cutoff but gradual reduction at the frequency you select. Using this control
properly can reduce “mud” and power-robbing, bass vibrating lows that
make your sound flabby, and encourage feedback. That satisfying thickness
on stage may mean your audience is just hearing rumble, and while that rich
maple syrup may taste good, it’s no fun to swim in it. Whether you need to
use one — and where you’d set it — will depend on your instrument and pickup, as well as the stage and setup (for
instance, whether you’re stuck in a corner).
Want to know more? Check out our FAQ about High-Pass Filters.
Enhance, Shape, Contour… These are a sample of labels you’ll find on some amp knobs, most of which change the
tonal character of your signal by boosting high and low frequencies and cutting the midrange. In my experience they
seldom help the sound of upright bass — which in my opinion needs those midrange frequencies to help define its
character in a live performance mix — and they often impart an “electric bass” or otherwise generic tone. Switches
or buttons like Deep, Bright, etc. will also apply a specific tone shape, which can also be kind of radical for upright.
Learn these tools by setting all of the amp’s tone controls at neutral, and try each of them using the techniques
discussed in the beginning of this e-Guide.
A FEW OTHER RELATED TOOLS
These last few common amp features are not specifically involved in tone, but it’s good to know what they do:
Phase Switch: When a signal is “in phase”, a note you play pushes sound waves (we’ll visualize it as “air” for the
sake of easy comprehension) from your bass into the room, and the vibration of your amp’s speaker also pushes
similar “air” out into the room. A Phase Switch (also called a “Phase Reverse”, “Invert Switch,” etc.) reverses the
signal’s phase, so when you play a note, the speaker more or less pushes air “in” while your bass is pushing out (and
vice-versa). Reversing phase may or may not result in a big change to your sound. But since it is the opposite from
your bass’ vibrations, it doesn’t “couple” with the bass and make your bass vibrate more. In practical use, the use of
reverse phase may help you gain a little more volume before you get feedback, but don’t expect a miracle.
Another use for a phase switch is when one is using two pickups, or a microphone with a pickup. Different devices can
be inadvertently wired in or out of phase, and if the phase is not the same it will usually rob you of bass response or
balanced tone. If you suspect this condition, switch the phase on one channel and listen to the result. The Euphonic
Audio Doubler has a Phase Knob, which changes phase gradually from one extreme to the other, for more precise
adjustments.
Active noise-cancelling headphones use this principle of phase reversal by reproducing
what they “hear” (on built-in microphones) in reverse phase, thus effectively “cancelling”
the sound in your headset.
Make Friends With Your Amp – by Bob Gollihur
Courtesy of Gollihur Music • www.GollihurMusic.com • ALL MATERIAL ©COPYRIGHT 2012 BOB GOLLIHUR