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Scheps Omni Channel: 7 Surprising Guitar Processing Tips

Dec 22, 2019

Scheps Omni Channel is a great all-around channel strip. Yet its flexibility allows for unconventional applications too: here we explore 7 unusual things it can do for guitars—from truly authentic wah, to acoustic-type dynamics for electric guitars, to monster sustain.

Scheps Omni Channel: 7 Surprising Guitar Processing Tips

by Craig Anderton

Channel strips are usually thought of as all-purpose, general modules that can form the core of a great mix. While the Scheps Omni Channel does all the traditional channel strip functions, there’s additional flexibility that allows using it in unconventional ways. I’ve found the Omni excels with guitar for such functions as nailing the characteristic sound of a vintage wah, tailoring compression specifically to the guitar’s frequency response, emulating out-of-phase pickup tones, pre- and post-processing for amp sims, and much more.

The Scheps Omni can choose among stereo, dual mono, and mid-side modes. Guitars are naturally mono, but with a mono signal, the Omni doesn’t really care if it’s in stereo or dual mono mode. I prefer to convert mono guitar tracks into dual mono, because I try to live in a two-channel world as much as possible; however the following techniques also work with mono guitar tracks.

1. Authentic Wah Pedal

Some people think all you need for a wah pedal emulation is a parametric EQ, a high Q setting, and some gain—then just rock the frequency control. However, a parametric filter stage doesn’t produce the same kind of curve as something like the legendary Clyde McCoy wah pedal. Its response curve fell off on both sides of the bandpass filter, more like what would happen if you ganged together a highpass and lowpass filter in series (e.g., the way the original Moog modular synths created bandpass filters; see Fig. 1). With a parametric, there’s no rapid falloff above and below the parametric bandpass stage.

A wah pedal’s bandpass response is not like a parametric’s bandpass, due to the rolloff above and below the center frequency

A wah pedal’s bandpass response is not like a parametric’s bandpass, due to the rolloff above and below the center frequency.

The trick to creating a true wah pedal sound with the Omni is to use it in DUO (dual mono) mode with a mono, or dual mono, guitar track. Switch one of the inputs out of phase. Both channels will cancel, and you won’t hear anything—so now when you introduce a bandpass filter, its response will be all you hear. Choose Parametric mode for one of the EQ stages (outlined in blue; see Fig. 2).

The Scheps Omni Channel is emulating a vintage, collectible wah pedal. The polarity flip parameter is outlined in yellow, and the wah filter itself, in blue

The Scheps Omni Channel is emulating a vintage, collectible wah pedal. The polarity flip parameter is outlined in yellow, and the wah filter itself, in blue.

Turn up the gain, turn up the Q, vary the frequency, and now your wah will be funky enough to score a Shaft movie remake, or rockin’ enough to channel Hendrix. Just remember that vintage wahs covered a limited frequency range; to stick with tradition, you won’t want to go much lower than about 300 Hz, or higher than 1.5 kHz.

2. A Better Compressor

Humbucking pickups are great, because they buck hum. They’re also excellent with distortion, because of their warm, fat, bass-heavy sound. However when compressing a dry guitar, the low frequencies take over a compressor; and unless it’s a multiband processor, this attenuates the highs as well. The sound doesn’t let the higher strings ring out, lacks smoothness, and can even sound muffled.

The Compressor’s sidechain option of the Scheps Omni offers a solution. This can boost the guitar’s low end, and use only the low frequencies to trigger heavy compression, so there’s not as much compression in the high frequencies. You’ll need to increase the Output level to raise the overall level, but the high frequencies will be more balanced with the low frequencies, because the low frequencies are so compressed.

Note the massive bass boost in the sidechain, using both bandpass and low shelving filters; and note that sidechain filtering is enabled

Note the massive bass boost in the sidechain, using both bandpass and low shelving filters; and note that sidechain filtering is enabled.

Furthermore, this approach handles transients better. Listen to the audio example; the first half of the example uses the Compressor without the special sidechaining, while the second half has the same settings (except for the sidechain being enabled), and the boosted output. Not only does the second half sound smoother and has more highs, but believe it or not, both halves reach the same peak levels—because the sidechain-enhanced compression handles transients and attacks better.

This approach is a natural for jazz guitar (e.g., Wes Montgomery, Jim Hall), which gravitates toward a bassier, mellower tone. But with rock, it also works well as a front end for amp distortion. The smoother tone leads to smoother distortion, which is particularly apparent with power chords.

3. Acoustic-Type Dynamics for Electric Guitar

I’ve always considered acoustic guitar and electric guitar almost as different as piano and synthesizer. When you play acoustic guitar dynamically, the timbre changes as well as the level—the harder you play, the brighter and more present the sound. Electric guitars don’t respond in the same way—but the Scheps Omni can make electric guitars more dynamic and responsive.

This technique takes advantage of being able to run two separate processing channels through the Scheps Omni Channel, and then combine the two into a single mono channel (Fig. 4). One channel is the dry electric guitar signal; the other goes through the Expander, followed by EQ. The Expander lets through only the peaks of the guitar’s strumming.

The Scheps Omni modules used for dynamic range and brightness enhancement

The Scheps Omni modules used for dynamic range and brightness enhancement.

The settings are pretty critical, and of course they depend on the input level. The expanded sound needs to be dynamic, yet smooth. Try about 10 ms of Attack, and around half a second of Release (less for a more percussive effect, more for a smoother one). The Threshold is crucial; too high a setting will give a stuttering sound, while too low a setting will let most of the signal through, not just the attacks. In the expander channel you’re not using, turn Threshold all the way down, and Floor all the way up to defeat the expansion action.

The Expander feeds a channel with EQ that emphasizes the high frequencies. Set this to taste; I prefer a pretty bright sound that’s mixed down far enough to support, not overtake, the dry channel. Set the output mode to Mono, and turn off Lock so you can adjust the left or right inputs (or outputs) to choose the desired balance of the dry and processed sounds. The audio example’s first half is the dry guitar sound, the second half has the enhanced dynamics. Note that the effect is exaggerated on purpose to make it obvious; in a real-world project, you’d probably want to be more subtle.

4. Out-of-Phase Pickup Emulator

Maybe you’ve wished you could get the bright, glassy sound of out-of-phase pickups—but rewiring guitars is a hassle, and besides, you don’t want to void your warranty or hurt the resale value. But if your guitar doesn’t have an out-of-phase switch, or you’re a keyboard player and want to coax this sound out of a sampled guitar, you don’t need to rewire your guitar when you have the Scheps Omni.

Of course, an exact out-of-phase sound depends on the pickups, scale length, strings, and other factors. This sound is based on analyzing the out-of-phase sound on an older Les Paul Standard, and profiling its frequency response. In general terms, an out-of-phase pickup cancels most of the bass, has a deep, broad cut around 1 kHz, and the response climbs steadily up from there. The higher the frequency, the less cancellation, and the brighter the sound. With the EQ curve in Fig. 5, use the middle pickup position (both pickups) for the most realistic effect.

EQ settings to emulate an out-of-phase pickup sound

EQ settings to emulate an out-of-phase pickup sound.

The only module we need is the EQ. The settings shown above are:

High shelf: Gain = +7.9, Frequency = 2,053
Mid peak: Gain = +9.7, Frequency = 6,239
Tone parametric: Gain = -18, Frequency = 1,200, Q = 0.61
Low shelf with resonance: Gin = -18, Frequency = 134

Naturally, this is ripe for experimentation, depending on the pickups you’re using, and the target sound. One big advantage over rewiring is that the Scheps Omni’s output control can compensate for the level loss caused by cutting out so many of the lower frequencies.

5. Amp Sim Pre/Post-Processing

One of the Scheps Omni’s coolest features is an insert slot that accepts many Waves plugins. We can put the GTR amp in there, and condition the sound both going into and coming out of GTR.

Many guitar players find amp sims suitable for single-note leads, but not so much for power chords. This is because the complex collection of frequencies causes intermodulation distortion that pushes amp distortion algorithms to the limit. However, restricting the high frequencies going into GTR with the Omni’s lowpass filter gives a smoother, sweeter distortion sound with power chords. In Fig. 6, the highs roll off at 625 Hz, with an 8 dB/octave slope. Although this reduces brightness, we can use EQ after GTR to bring the highs back up again—the resonant shelf is ideal for this. Because the sound we’re processing is sweeter, bringing up the highs quite a bit doesn’t accentuate any undesirable artifacts. I also like to trim the low end a bit below the range of the guitar (the highpass filter is set around 70 Hz).

Trimming the frequency response in the Pre prior to GTR, then using EQ after GTR, gives a sweeter power chord sound

Trimming the frequency response in the Pre prior to GTR, then using EQ after GTR, gives a sweeter power chord sound.

The audio example’s first half bypasses the Omni processors, while the second half enables them. The Omni reduces “spikiness,” and gives a smoother, less inharmonic sound. You’ll really notice the difference if you play the first half again, after hearing the second half.

Furthermore, although not used in this example, don’t overlook how useful de-essing can be to reduce a guitar’s highs as you play louder. It’s very much like an “intelligent” version of the way guitar players roll down the tone control to reduce treble, and create a “creamier” tone. This is particular useful with VOX AC30 emulations, which have a naturally bright sound. Taming this brightness allows the amp to be used in a wider variety of musical contexts.

6. Drum Triggering

Let’s take advantage of the sidechain with power chords. In this example, drums provide a sidechain signal to trigger the post-amp gate, which “chops” a power chord rhythmically with the beat. The Gate is set to External Sidechain (Fig. 7).

Drums trigger the Gate in time with the music

Drums trigger the Gate in time with the music.

Threshold sets the level at which the drums trigger the gate, and this lets the guitar through. For a more percussive effect, lower the Threshold, and shorten the Release time. Attack should be long enough to prevent “chattering,” and give a smooth gating sound. There are a lot of variables here, and you can tailor the sound from a super-percussive effect, to something with a longer Release and higher Threshold that follows the drum’s overall dynamics instead of individual hits.

7. Monster Sustain

And finally, what guitarist doesn’t want sustain? Fortunately, you can push Omni well beyond the boundaries of polite taste, and obtain monster sustain (Fig. 8). Turn Threshold all the way down, Ratio up really high, and since we’re feeding the GTR Overdrive amp, let’s overdrive the Overdrive by kicking the output up to 12 (yes, Spinal Tap fans—that’s one better than going up to 11).

The Omni is providing massive amounts of sustain

The Omni is providing massive amounts of sustain.

Also note that the Expander is in play. With this much sustain, the sound gets pretty noisy toward the end of the string decay, so we want it to make a graceful exit. Because the compression raises the sustain so much, the expansion can start at a fairly high threshold to get rid of the noise and hum at the note’s tail, and still preserve most of the sustain.

In this case, an audio example isn’t all that meaningful, because all you hear is that one chord lasts a lot longer than the other. So, Fig. 9 makes it easier to visualize exactly how much the sustainer is affecting the guitar (and note the timeline at the top for reference). It’s a dramatic difference.

The compressed sound on the bottom has much longer sustain, and an overall higher average level

The compressed sound on the bottom has much longer sustain, and an overall higher average level.

Yes, the Scheps Omni does everything you’d expect a channel strip to do with drums, vocals, bass, and the like. But hopefully, the preceding shows just how flexible this plugin can be—and how far you can push it—with guitar.

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