MathAudio Guitar EQ

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Guitar EQ Help

This tutorial will help you detect and compensate for the unwanted resonances of your guitar.

The body of classical and acoustic guitars is an acousto-mechanical resonator that amplifies sound generated by strings by means of multiple resonances. Ideally, these resonances should be uniformly distrubuted along the frequency range and have similar gains. In reality, however, some of these resonances usually have too large gains. Our experiments have shown that one or a few strong resonances can destroy the guitar sound because of so-called "masking effect". We've also found out that the digital correction of the largest guitar resonances can substantially improve the quality of the guitar recordings. MathAudio Guitar EQ plug-in helps you to detect and compensate for the unwanted guitar resonances.

You need:
- A conventional plastic pick (1mm). You need such pick even if you don't use it for playing the guitar.
- A pair of good closed headphones. If you don't have such headphones, a pair of famous Sony MDR-7506 is a safe choice. You can also use MathAudio Headphone EQ to improve the quality of the monitoring.
- A good condenser microphone or a piezo pickup. We don't recommend using dynamic microphones because they have a low signal-to-noise ratio.

If everything is prepared, the further steps are as follows:

1. Install one of the following packages:
- Install Guitar EQ VST plug-in if you want to use it with a VST compatible host software. If you work on Windows, the version of your VST plug-in (x32 or x64) must correspond to the version of your host software.
- Install Guitar EQ AU plug-in if you want to use it with an AU compatible host software.

2. Connect your headphones to the sound card of your computer

3. Connect your microphone or piezo pickup to the sound card of your computer

4. Start the Guitar EQ plug-in
Create a new empty project in your DAW. Adjust the direct monitoring of your microphone or pickup. Make sure that you hear the sound in your headphones when you play the guitar. Then include the Guitar EQ VST/AU plug-in to that project and open the plug-in window in accordance with the manual of your host software.
Guitar EQ plug-in
Fig.1. Screenshot of the MathAudio Guitar EQ VST/AU plug-in.

5. Check the presence of the microphone/pickup signal
Make sure that the "Input signal indicator" shows the presence of the mic signal in a green color as it is shown in Fig.1.

6. Measure the frequency response
Click the "Start measurement" button. Use the back side of your pick to knock your guitar's bridge saddle between 3rd and 4th strings as it is shown in Fig.2. Don't use your nail or other things for knocking. Use only a conventional plastic pick. The sound must be loud enough. Your free hand must suppress the sound of strings as it is shown in Fig.2. Listen to the example sound here.
Guitar EQ
Fig.2. Measurement.

The measurement process takes 5 seconds. You will get the plot of frequency response as it is shown in Fig.3 (your plot will be different).
Guitar EQ plug-in
Fig.3. Composite frequency response of guitar, room and microphone (the frequency response of your guitar, room and microphone can be very different).

It is easy to see that the frequency response in Fig.2 contains a few strong resonances. The resonance between 200 and 300 Hz is most harmful because it creates a "boomy" sound.

7. Add a reverb plug-in if you need it
If you are going to apply a reverb to the sound of your guitar, add the reverb plug-in now (after the Guitar EQ).

8. Move down the vertical slider and adjust the position of the "Brightness" slider
Wear your headphones. Move down the vertical slider and release it to cut out some part of the main resonances as it is shown in Fig.4. Play your guitar and find the best position of the vertical slider. Then find the best position of the "Brightness" slider. Repeat this process a few times to make sure that both sliders are in their optimum position. Try to activate the "Cut and boost" mode which sometimes works better than the "Cut only" mode.
Guitar EQ plug-in
Fig.4. Original frequency response (gray line), reference response (green line) and resultant response (white line).

9. Manually correct the reference curve
This step is necessary to fine-tune the timbre of the guitar. You can modify the built-in reference frequency response and listen to the result. MathAudio Guitar EQ contains a convenient tool for drawing your own reference frequency response. Just move the cursor of your mouse to the frequency response window, press the left button of the mouse and draw your own frequency response. You can also use the right button of the mouse to draw straight lines. An example of the changed reference curve is shown in Fig.5.
Guitar EQ plug-in
Fig.5. Manually changed reference curve.

10. Compare processed sound of your guitar with its original sound
Make sure that the "Guitar EQ" radio button is selected as it is shown in Fig.6 (a). Play music. Remember the loudness of the processed sound of your guitar. Then click the "Bypass" radio button to listen to the original (unprocessed) sound and move the "Bypass signal volume" slider left until the loudness of the original sound becomes equal to the loudness of the processed sound: equal loudness is necessary for correct comparison of the processed and original (unprocessed) sounds. Switch "Guitar EQ" and "Bypass" radio buttons and adjust the position of the volume slider until the loudness of the processed sound will be equal to the loudness of the original (unprocessed) sound (see Fig.6 (b) and (c)). Compare the qualities of the processed and original (unprocessed) sounds.
Guitar EQ
Fig.6. Making audio test.

11. Save preset
Select the "Guitar EQ" radio button and click the "Save preset" button to save the accurate state of the plug-in as a .gtr file. This file will help you to restore the state of the plug-in if necessary.