Notch FiltersUpdated 9 months ago

Eliminating Feedback With Notch Filters

Notch Filters

Some guitars might experience feedback when using the ToneWoodAmp for the same reasons a guitar feeds back with an amplifier or PA. Notch filters can isolate and attenuate feedback frequencies, letting you attain a better overall sound at higher levels. 

The ToneWoodAmp’s notch filters can be used creatively as an EQ, but its primary function is to attenuate frequencies causing feedback.

The ToneWoodAmp offers two programmable Notch Filters:

• Notch 1 operates in the range 100 Hz –1.1 kHz

• Notch 2 operates in the range 200 Hz –2 kHz

NOTE: The Notch Filters do not affect the DI signal out of the ToneWoodAmp.

Using the Notch Filters

To access and program the Notch Filters:

1. Enter the Notch Filter menu by pressing and holding the Amplitude knob for two seconds.

Filters> appear on the display.

2. Turn the Amplitude knob clockwise to select Notch 1 or Notch 2.

Once you select, each ToneWoodAmp knob assumes a new role in con-
trolling the filter’s parameters. (see the "default" actions on the front diagram connected to the notch filters)

• Effects knob will now CUT the selected frequency, increasing attenuation by turning clockwise from 0 to 20.

• Parameters knob will set the notch filter frequency (FREQ). The values change in 40 Hz increments. Click the Parameters knob ONCE and the values now change in 4 Hz increments, making it easier to accurately hone in on problem frequencies.

• Amplitude knob still controls the relative VOLUME of the selected filter. This is useful when identifying problematic feedback frequencies, or simply turning up or down the feedback while setting the filters

Eliminating Feedback
A common practice to find and fix feedback is to search for the problematic frequencies by selecting a narrow band, sweeping across frequencies until the feedback disappears, and then applying the appropriate amount of cut at that frequency. This is known as the Search and Destroy method.

To Eliminate feedback using the Search and Destroy method:

1. Enter the Notch Filter menu by clicking and holding the Amplitude knob for two seconds.
    Filters> appear on the display.

2. Turn the Amplitude knob clockwise to select Notch Low.

The Amplitude knob now controls the filter’s volume.

3. Although rather annoying, turn Amplitude clockwise and let the feedback continue.

4. Turn the Effects knob fully clockwise until the cut value reaches 20 (the maximum amount of attenuation).

5. Slowly turn the Parameters knob to scan through the frequency spectrum until the feedback
    starts to dissipate.

It can be helpful to click the Parameters knob to toggle into fine-tuning (4 Hz increments) and scan until you find the frequency with no feedback.

6. With the problematic frequency identified, slowly turn the Effects knob counterclockwise to reduce 

    the amount of attenuation until the feedback starts to become audible again.

7. Now turn the Effects knob clockwise a few notches until it goes away again.
    You have found the minimum cut to avoid feedback without altering the tonal balance of the
    ToneWoodAmp’s effects.

8. Click the Amplitude knob to save your changes.
    Notch Filter settings are automatically saved to individual Guitar presets.

9. If you notice another problematic frequency, select Notch High and repeat Steps 3 through 8.

NOTE: The Notch High filter is set by default to cut 900 Hz as this seems to be a typically problematic frequency between the ToneWoodAmp and most guitars. However, this is just a starting point so feel free to adjust it.
Once you tame these frequencies, you can turn up the volume of the ToneWoodAmp much louder without feedback, as well as increase the Master Gain to produce more volume. As an added bonus, you are now familiar with the Search and Destroy method, which comes in very handy in many audio situations.