You don't always need fancy signal processors to emulate some common guitar sounds and effects. Sometimes, off the shelf programs or effects can do the job. For example...

Vintage wah effects. You can’t get a vintage wah sound just by sweeping a highly resonant parametric EQ set to bandpass, as real wah pedals have steep response rolloffs that reduce both high and low frequencies. To emulate this effect with modern parametric EQs:

• Copy the guitar track so you have two cloned tracks set to the same level.
• In track 1, insert a parametric EQ set to bandpass (peak/dip) mode with about 6dB gain and Q (resonance) of around 8.
• Flip track 2 out of phase.
• Sweep the EQ over a range of about 200Hz–2.2kHz.

Throwing one track out of phase causes the high and low frequencies to cancel, so all you hear is the filtered midrange sound—just like a real wah.

Adding “air.” When recording guitars direct, there aren’t mics to pick up the room reflections that give a “you are there” vibe. To model these reflections:
• Feed your guitar track through a multitap delay plug-in (or use several individual delays).
• Set the taps for short, prime-number delays (3, 5, 7, 11, 13, 17, 19, and 23 milliseconds) to avoid resonant build-ups.
• For more air, add some feedback (but not enough to hear individual echoes). Experiment with the tap levels and pans, and then mix the delayed sound in at a low level.

Closed-back to open-back cabinet.With open-back cabinets, low-frequency waveforms exiting through the cabinet back partially cancel the low-frequency waveforms coming out the front. Emulate this effect by reducing bass somewhat. A low-frequency shelving filter works well.

Out-of-phase pickups. Don’t have an out- of- phase switch? You can come close with a studio-type EQ.
• Select both pickups.
• For the EQ, dial in a notch filter around 1,200Hz with a fairly broad Q (0.6 or so) and severe cut—around -5dB to -18dB.
• Use a high shelf to boost about 8dB starting at 2kHz, and a low shelf to cut by -18dB starting at 140Hz.
• Tweak as needed for your particular guitar and pickups.
• Boost the level—like a real out-of-phase switch, this thins out the sound.

Big bass build-up. When a cabinet is close to a wall, bass waves bouncing off the wall reinforce the waves coming out the cab’s front. This can produce a rumble—due to walls and objects resonating—that EQ can’t imitate. For a killer rumble, split your guitar signal through an octave divider, then follow the octave divider with a lowpass EQ set to cut highs starting at 120Hz. This muddies the bass sound further. Then, mix the octave sound about -15dB below the main signal—just enough to give a “feel” of super-low bass.

For a vintage wah sound, split the guitar through two tracks, flip the phase switch (outlined in green) on one track, and insert a parametric EQ (outlined in magenta) with a resonant bandpass response in the other track.

This EQ curve emulates the sound of out-of-phase pickups.