Fairfield Circuitry Shallow Water – Chorus and Modulation

The Shallow Water’s essence is uncertain, subtle and nostalgic, because the effect builds around a typical analogue chorus and vibrato circuit.

Secondly, another signal then modulates this delay time to create changes in pitch.

The original signal mixes with the chorus effect and this is what makes the effect really striking. The delayed signal modulates in a random fashion which gives “that special sound”.

See it in action here.

How does it work?

Pseudo Random Generator

The random quality of the effect begins in a simple program which creates random voltage steps. The RATE control effectively sets the overall range of these time intervals.

Integrator & Depth

A filter processes these random stepped voltages, giving control over the slope at which the steps will reach their new values.

Increase DAMP and random steps are sluggish instead of sharp and abrupt.

DEPTH defines the amount of modulation which changes the time delay of our input signal.

There is a strong link between all three controls, RATE, DAMP and DEPTH, because they all affect modulation.

Envelope Follower and Recovery Filter

A recovery filter removes unwanted bucket brigade device noise as it follows the input envelope.

The LPG control sets the envelope and yields a bouncy, lo-fi response to quick and snappy gate-like behaviours.

Rate:

The RATE control adjusts the time intervals at which the random pitch fluctuations occur. From rare to nervous, the range is quite wide. At high RATE and DAMP settings, the quick variations have trouble passing through the swampy filter and integrator, effectively reducing perceived modulation. This is normal. The link between these two knobs needs to be tamed through experience.

Damp:

The DAMP control affects the slope of the modulating signal. At its minimum, the pitch changes are quick and sudden and the random changes in voltage almost immediate.

Increase DAMP to soften the modulation. At high DAMP settings, the changes become so slow that cannot be heard as modulation. Then, mix in some dry signal and hear the chorus.

Depth:

The DEPTH knob adjusts the intensity of the modulation. The link between all three modulation controls is noticeable and the range of modulation focused towards subtle variations. Adjust to taste, though less is more.

LPG:

The LPG control adjusts the level of the envelope feeding the low pass filter and gate circuit. At lower levels, the signal is darker, chokes subtle notes and reduces sustain.

At higher settings, the sound is brighter, with more sustain and often reveals some noise produced by the bucket brigade device.

Mix:

The MIX control balances the dry and wet signals. When it’s full wet, the effect is like a vibrato. Add more dry signal for chorus-type sounds.

Volume:

The VOLUME knob controls the output volume with unity around noon and beers around 5 at my place.

Boost & Pad:

There are two jumpers at the input stage to match your input signal’s level and impedance. By default, BOOST is on and PAD is off, because this is a typical setting for high impedance, low output signals like a guitar’s single-coil pickups.

If the user finds there is too much distortion at the input stage, moving the BOOST jumper to its off position will reduce overall gain by 6 dB. If the signal source is line level, the PAD is set to its on position, giving another 6 dB of gain reduction.

LPG Adjust:

Fine-tune the way it reacts to incoming signals with the LPG Adjust. Lowering this frequency emphasises the action of the low pass filter and raises the threshold of sensitivity.

Use these settings. MIX full wet, LPG minimum and DEPTH minimum. While listening to a signal going through the pedal, you’ll hear the effect of the recovery filter at its resting state.

Carefully turn the trimpot labelled LPG adjust, clockwise to raise the filter’s frequency, and counter-clockwise to lower.  The trimpot is very sensitive, so make small adjustments. After each adjustment,  turn it up momentarily and listen to the envelope’s response to the incoming signal.