BASS AND TREBLE CONTROLS
The Bass control cuts or boosts the lower or bass frequencies. Starting at mid-position, turning the control counter-clockwise cuts the bass response and turning the control clockwise boosts the bass response. The Bass control is a “shelving” type tone control, with the shelving point set at about 120Hz.
The Treble control is also a shelving tone control whose shelving point is about 2.5kHz. Starting from mid-position, turning the control counter-clockwise cuts the highs and turning the control clockwise boosts the high frequencies.
A center “click” position on both the Bass and Treble controls indicates flat frequency response, which means NO cut or boost is being heard on that control.
3-BAND SEMI-PARAMETRIC EQUALIZERS
There are two 3-band semi-parametric EQs in the SM-900. They can be thought of as adjustable bass, midrange and treble knobs. The bottom 3 are designated “EQ 1” and the top three and des- ignated “EQ 2.” These may be selected by either the footswitch or the manual slide switch located on the front panel.
The term “semi-parametric” in this case means that it has a cut and boost function and a frequen- cy select function. If a bandwidth (Q) control was added, it would become a fully parametric equal- izer. A graphic EQ is similar to tone controls such as the Bass and Treble controls, except that it uses slide controls or “faders.” The semi-parametric has the advantage of allowing you to select which frequency is cut or boosted by the level control. A regular equalizer has fixed center frequen- cies and cannot be altered by the user.
On each band of the semi-parametric EQ there are two concentric knobs. The inner knob is the LEVEL control. It cuts or boosts the frequency set by the FREQUENCY control, which is the outer knob. If the LEVEL control is in its flat, center-click position, that band will be essentially off. Moving the frequency (outer) knob with the level control in the flat position will have NO AFFECT on the sound or tonal structure. The level control MUST be in a cut or boost (off center) for any change in tone to be audible.
FEEDBACK AND/OR SUSTAIN:
The low mid to hi midrange areas (80 Hz to 1 kHz) found on the semi-parametric EQ can be extremely useful in correcting feedback in acoustic bass guitars or upright basses. If you are get- ting a slight amount of feedback from your instrument, try the following:
Set your volume to a point where the feedback is just occurring, but not out of control; raise the Level control of the first or second band of the parametric EQ that is activated to about +7 dB; slowly rotate the Frequency control from left to right. At some point on either the first or second band during the rotation of the Frequency control, the feedback should get more intense. This is the frequency area that needs attention. Leave the Frequency control at the position the feedback gets louder; now adjust the Level control in the CUT mode until the feedback disappears. You may find that as you raise the volume, you may need to further cut the Level control to achieve the desired playing volume. In this example, when the feedback becomes more intense, make sure it is the same “pitch” as the original feedback. Feedback can be induced at different frequencies by boosting them and you certainly don’t need two problem areas.
By reversing the technique above, you can achieve greater sustain in certain areas or on certain notes. You can also use these guidelines to correct hot or dead spots on the neck of your instru- ment or inherent in your speaker system.