Merlo’s Tone Shaping (Using The Color Control)

In a traditional harmonic tremolo, the sound is divided into high and low frequencies and the output fades between the high part and the low part. It’s a simple idea, and it sounds great.

In the original Fender “Brownface” tremolo, and other harmonic tremolos, the crossover frequency of the high pass and low pass parts of the signal is fixed in one place. The shape of these filters is also fixed, and you mostly just have control over speed and depth.

Merlo allows setting the crossover frequency, as well as the resonance and roll-off of the high and low pass filters. It also uses a more complex filter design that adds subtle (and sometimes pronounced) formants to the sound.

What are formants?

Formants are frequency peaks that stay fixed at specific frequencies even when the sound changes pitch, as opposed to overtones which change frequency with the fundamental pitches. Formants occur naturally all around us, and are responsible for much of the tonal character of everything from acoustic instruments to speaker cabinets.

Formant frequencies can also move dynamically in natural environments. This is still different from overtones, because the frequencies are defined by changes in the acoustic environment, not by the fundamental pitches of the sound.

What are examples of dynamic formants?

One great example is the human vocal tract. Formant resonances in the vocal tract are the reason you can hear different vowel sounds (ooo - eeee - ahhh). Another example is the Leslie speaker cabinet, which typically contains both a moving horn speaker and a moving speaker baffle, which continually change the shape of the cabinet and the formants produced.

While a Leslie cabinet or vocal formats are both good examples of how formants can change or move dynamically (and great examples of why this sounds pleasing to the ear), Merlo doesn’t seek to emulate a Leslie cabinet or a vocal tract. Merlo’s purpose is to produce a harmonic tremolo that imparts warmth and brightness and a whole range of tonal character in an organic and musical way that stays true to the idea of a harmonic tremolo.

With formant shaping applied independently to both the primary and secondary voice of the harmonic tremolo, Merlo’s tonal shaping is more integrated and responsive than a pre or post EQ, and is also interacting dynamically with the movement of the tremolo. This imparts textures that you can’t get from other tremolo designs or from an external EQ.

What does the Color control do?

The filters that power Merlo are capable of a very wide range of settings. Trying to give full control over these would require a dozen knobs, and it would be tedious to dial in something usable. We have curated a “best of” collection of parameter combinations and have provided a continuous sweep through these via the Color knob. 

The Mode toggle sets three different modes for the Color control. 

The first mode sweeps from a standard amplitude tremolo (flat full bandwidth primary signal, and no secondary signal) to a conventional harmonic tremolo (simple high pass/low pass configuration.) 

The second mode employs the formant shaping we’ve been talking about, and the crossover frequency and voicing of the formants changes throughout the sweep of the Color control.

The third mode also sweeps through a range of voicings, but with a bandpass configuration instead of high pass for the primary voice. This creates an overall low pass contour for the tremolo. The low pass roll-off ranges from more subtle to more apparent depending on the Color control.

A demo is worth a thousand words. Check out some examples here.