Trace Acoustic TAB100 Manual De Instrucciones página 4

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Hi Trim/Lo Trim Channel 2
The HI and LO TRIM controls have been provided to "trim" the sound from the user's
instrument/pickup combination to achieve a fundamentally flat response prior to any tailoring of
the sound with the graphic or shape facilities.
The HI TRIM controls on CHANNEL 1 and CHANNEL 2 have been set at different frequencies to
allow the two channels to be used for different purposes, e.g. CHANNEL 1 as a "plucked" input
and CHANNEL 2 as a "bowed" input. This arrangement is also useful for treating the outputs of
two independent pickups separately. Some upright bass players prefer to mount a second piezo
pickup under the fingerboard of their instrument to amplify the percussive "slap" produced by
some playing techniques. Channel 2 allows the second pickup's output to be independently
processed in this situation.
Graphic Equalisation
The five bands of graphic equalisation offered, have their centre frequencies chosen specifically to
suit the acoustic guitar signal and may be used to adjust the sound of the instrument to your
liking.
Avoid extreme settings on any slider as these are unlikely to give any useful results.
Notch Filter
All models in the Trace Acoustic series include a NOTCH FILTER that can be switched IN or OUT.
This is included as an anti-feedback device to allow amplification of an acoustic or double bass
without trouble from feedback caused by the resonance of the body of the instrument.
What is a NOTCH FILTER? Basically, what a NOTCH FILTER does is to remove a very narrow band
of frequencies from the response of the amplifier. If this band of frequencies is narrow enough it
will not be missed from the wide band of frequency response of the unit. This band, of "notch", is
then made tuneable so that it can be adjusted to the resonant frequency of the body of the bass,
thus reducing the amplification at that particular frequency and eliminating the feedback.
Why is this necessary? Most pickups on an acoustic or double bass are usually mounted on or
near the bridge of the instrument, at the centre of the front of the soundboard. This picks up the
vibration of the strings but also picks up the vibration of the soundboard itself. The soundboard,
being a relatively large area, will also pick up the sound of the speaker. This will be amplified via
the pickup and amplifier and cause feedback to occur at the resonant frequency of the
soundboard.
Each instrument will have its own resonant frequency and it is this frequency that you must
adjust the NOTCH FILTER control to find. The most effective way of doing this is to deaden the
strings of the bass, turn the amplifier up loud until feedback occurs, switch in the NOTCH FILTER
and adjust it until the feedback disappears. This has then set the NOTCH FILTER to your particular
instrument.
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