There are two Main filter modules, labelled Filter 1 and Filter 2.

The outputs from all four Sources are sent (in varying amounts, according to their respective FilterMix settings) to the Main filters.

Both Main filter modules provide multi-mode filters with identical controls. Each one has its own FX-Mix control, which (like the FilterMix control in a Source) works as a kind of two-channel mixer, or crossfader.

• With the FX-Mix control turned all the way to the left, all of the filter’s output is sent to Alchemy’s main output, and none of it to the Effects module.
• With the FX-Mix control turned all the way to the right, all of the filter’s output is sent to the Effects module, and none of it to Alchemy’s main output.
• With the FX-Mix control set half-way, equal amounts of signal are sent to the Effects module and Alchemy’s main output.

Finally, the Par/Ser knob acts as one more crossfader, allowing you to send the non-FX portion of the Filter 1 signal to the Output stage (when Par/Ser = 0%), to the input of Filter 2 (when Par/Ser = 100%), or to a mix of these destinations (when Par/Ser has some intermediate value). Therefore:

• To use the Main filters in parallel — set the Source FilterMix controls as desired, set Par/Ser to 0%, and set the Filter 1 FX-Mix control as desired.

• To use the Main filters in series — set the Source FilterMix controls to ‘100% F1 0% F2’, set the Par/Ser knob to 100%, and set the Filter 1 FX-Mix control to 0%.

Note that when the Par/Ser knob is set to 100%, a portion of the Filter 1 signal will bypass Filter 2 whenever the Filter 1 FX-Mix control is set above 0%.

Global page controls

The Filter section on the Global Page provides access to the two Main filter modules, each of which offers a powerful multi-mode filter.

Identical controls are provided for Filter 1 and Filter 2:

• On toggles the filter unit on or off.
• The filter type selection field allows you to set each filter to one of 50 filter types (see ‘Filter Types’ below).
• The three primary filter controls are Cutoff, Res, and Drive. The meaning of these controls depends on the selected filter type (see ‘Filter Types’ below).
• FX-Mix controls how much of the filter module’s output is sent to Alchemy’s Effects section, and how much directly to the main Output.

Filter VU meters

Both Main filters include VU meters indicating the current audio level received from all four sources combined:

When the output from all four sources exceeds 0dB the VU meters will indicate clipping has occurred by momentarily turning red:

Clipping is an undesirable artefact of digital audio which occurs when the output exceeds 0dB or the input to an effect exceeds the maximum range, producing a nasty distortion like sound in the output stage. If clipping does occur, simply reduce the amplitude of the loudest source or adjust the balance of the sources using the Morph section.

Filters and filter types

Altogether, Alchemy provides a total of 15 multi-mode filter modules (two Main filters, four sets of three Source filters, and the MMFilter module in the Effects section). There are 50 filter types to choose from in the Main filters and the MMFilter module. The Source filters offer a smaller selection of filter types, and they lack the Drive control found in the Main filters and the MMFilter module.

You will find descriptions of all 50 filter types below.

Filter types: lowpass, bandpass, hipass

These filter types will be familiar to many users. A lowpass (LP) filter passes the portion of a sound below a specified cutoff frequency and rolls off the portion above that frequency. A bandpass (BP) filter passes the portion of a sound occupying a band surrounding the cutoff frequency and rolls off the portions above and below that band. And a highpass (HP) filter passes the portion of a sound above a specified cutoff frequency and rolls off the portion below that frequency.

There are 42 different LP, BP, and HP filter designs available in Alchemy, each with distinctive characteristics that you may prefer for a given purpose. The three principal filter controls have standard functions for all 42 of these filters:

• Cutoff controls the filter cutoff frequency.
• Resonance controls the filter resonance or emphasis, such that higher settings boost frequencies in the immediate vicinity of the cutoff frequency.
• Drive allows the filter to be overdriven; the precise effect varies with each filter design.

The available LP, BP, and HP filter designs include:

• LP2-BQ, BP2-BQ, HP2-BQ — 2-pole, bi-quad filters.
• LP2-Fat, BP2-Fat, HP2-Fat — 2-pole filters designed to saturate heavily at higher Resonance and Drive settings.
• LP2-SVF, BP2-SVF, HP2-SVF — 2-pole state-variable filters.
• Analog-modelled filters — there are several designs modelled on the filters in classic hardware synths. Each of these is available in two versions, a normal one and a 2x-oversampled HQ one (offering higher quality at the cost of greater CPU usage).
  • 2-pole analog-modelled filters — LP2-K20, BP2-K20, HP2-K20; LP2-XP, BP2-XP, HP2-XP; LP2-MG, BP2-MG, HP2-MG.
  • 4-pole analog-modelled filters (these provide a steeper roll-off of frequencies beyond the cutoff) — LP4-XP, BP4-XP, HP4-XP; LP4-MG, BP4-MG, HP4-MG.

Filter types: formant and peaking

The formant filter works like a bandpass filter with a potentially very narrow bandwidth. It is designed to mimic a formant, or fixed resonance, such as those produced by the hollow body of a guitar or by the shape of the vocal cavity (which is adjusted during speech to produce different vowel sounds).

• Cutoff controls the resonant frequency of the formant.
• Resonance controls the width of the band surrounding the resonant frequency. Low values produce a narrow band, high values a wider one. Setting the resonance too low may cause little or no sound to pass through the filter.
• Drive has no effect for this filter type.

Note: To create multiple formants, you can configure the Source Filters in parallel and set the type of all three filters to ‘Formant’. See the example at the bottom of this page, which uses multiple formants to mimic vowel sounds.

The peaking filter boosts a narrow band around some resonant frequency while leaving the rest of the signal more or less unchanged.

• Cutoff controls the resonant frequency of the boosted band.
• Resonance controls the amount of boost. Higher values are generally the most effective.
• Drive has little effect for this filter type beyond boosting the overall gain.

Filter types: comb filters

A comb filter mixes the original signal with one or more copies delayed by a very short time interval. At some frequencies this mixture causes phase cancellations, while at other frequencies it causes reinforcements; the result is a ‘spiky’ frequency response with multiple resonant peaks. (A graph of these peaks resembles the teeth of a comb, which gives this filter type its name.)

Alchemy offers two comb filter designs. CombP (P is for ‘plus’) uses positive feedback on the delay lines, while CombM (M is for ‘minus’) uses negative feedback to produce less extreme effects, often with a ‘hollow’ quality.

• Cutoff controls the delay time in the comb circuit (lower cutoff = longer delay).
• Resonance controls the amount of feedback in the comb circuit.
• Drive has little effect for the comb filter types beyond boosting the overall gain.

Note that sending a percussive sound into a highly resonant comb filter will cause it to ‘ring’ at a frequency determined by the delay time (hence controlled by the Cutoff knob).

Filter types: ring modulation

Ring modulation is a process in which a modulator and a carrier signal are multiplied. Each frequency component of the modulator interacts with each frequency component of the carrier to produce two sidebands: a sum and a difference (carrier – modulator). When an Alchemy filter is set to the RingMod type, the signal entering the filter acts as the modulator, while the carrier is supplied internally by the filter.

• Cutoff controls the carrier frequency.
• Resonance applies a constant offset to the carrier.
  • At 0% Resonance, the carrier wave varies between –1 and +1, and the result is classic ring modulation.
  • At 100% Resonance, the carrier wave varies between 0 and 1, and the result is classic amplitude modulation. In this case, the carrier signal itself is present alongside the sum and difference sidebands.
• Drive controls the carrier waveform.
  • Setting Drive to 0% gives a pure sinewave carrier. This setting is often the most useful for producing characteristic ‘bell-like’ timbres.
  • Setting Drive above 0% progressively truncates the carrier waveform (reducing it to just the first quarter of the sine shape when Drive is 100%). These settings produce a greater density of sidebands, typically resulting in noisy/grungy timbres.

Filter types: distortion

The Alchemy filters offer several distortion effects.

• Tube — implements the the well-known and well-loved ‘Tube’ distortion effect from CamelPhat.
• Mech — A more ‘metallic’ sounding distortion, also from CamelPhat.
• BitRed — A harsher sounding ‘bit reduction’ effect (also known as ‘bit crushing’).

Note that distortion effects created in the Source Filter and Main Filter stages of the signal path are ‘polyphonic’ — that is, each voice is distorted independently, so there are no intermodulation effects when you play chords with this kind of distortion. In contrast, the Distortion module in the global Effects stage at the end of the signal path processes a mix of all the voices.

The principal filter controls work as follows when the filter type is set to a distortion effect:

• Cutoff controls the intensity of the distortion effect.
• Resonance controls the mix between clean and distorted signals (0% = clean only, 50% = equal mix, 100% = distorted only).
• Drive has little effect for the distortion types beyond boosting the overall gain.

Example: Creating vowel sounds with parallel source filters

Vowel sounds in human speech are the result of formants produced by changing the shape of the vocal cavity. By mimicking these formants, Alchemy can produce speech- or song-like effects, even in VA mode (i.e. without relying on samples of actual speech). Here is a basic example.

• Initialize Alchemy by choosing the ‘Clear’ command in the Title bar’s FILE menu.
• Go to the Source A sub-page and adjust the following settings:
  • Increase Amp to 0 dB.
  • Set Coarse Tune to –12 semis.
• Click the Source A Fine Tune knob to bring its mod rack into view in Alchemy’s Mod section.
  • In the first mod-rack slot, choose ‘LFO’ > ‘LFO 1’, and adjust the mod depth to approximately 50%.
  • In the LFO 1 control panel, set Attack to approximately 0.50 sec, turn off SYNC, and set Rate to approximately 5 Hz.
• Turn on the Source A Filter section, and click the Filter button to bring the Source Filter details into view.
  • Turn on all three of the individual Source Filters, and set the configuration to parallel. We’ll come back to these filters and adjust the Cutoff and Resonance settings in a later step.
• Switch the Source section view to ALL. Click in the Source A content field and choose ‘Copy Source’. Then click in the Source B content field and choose ‘Paste Source’, click in the Source C content field and choose ‘Paste Source’ again, and click in the Source D content field and choose ‘Paste Source’ a final time.
• On each of the Source Filter sub-pages, adjust the following settings (all values are approximate):
  • Source A — ‘Ah’ as in father
    • Cutoff 1 = 800 Hz, Res 1 = 100%
    • Cutoff 2 = 1200 Hz, Res 2 = 100%
    • Cutoff 3 = 2800 Hz, Res 3 = 100%
  • Source B — ‘Ee’ as in peace
    • Cutoff 1 = 230 Hz, Res 1 = 100%
    • Cutoff 2 = 2600 Hz, Res 2 = 75%
    • Cutoff 3 = 3200 Hz, Res 3 = 75%
  • Source C — ‘Oo’ as in food
    • Cutoff 1 = 200 Hz, Res 1 = 100%
    • Cutoff 2 = 880 Hz, Res 2 = 65%
    • Cutoff 3 = 2400 Hz, Res 3 = 50%
  • Source D — ‘Eh’ (as in let)
    • Cutoff 1 = 530 Hz, Res 1 = 65%
    • Cutoff 2 = 1850Hz, Res 2 = 75%
    • Cutoff 3 = 2500Hz, Res 3 = 50%
• Now that each Source is configured to produce a vowel sound, let’s set up morphing between these sounds and control it via the modwheel.
  • Switch the Source section view once more to ALL. Set the MORPH mode to ‘morph linear’ and set the X knob (the only knob) to 0%.
  • The Morph X knob’s mod rack should now be in view in the Mod section. Since the modwheel is linked by default to Performance Control 7, click in the first mod-rack slot and choose ‘Perform’ > ‘Control7’. Leave the mod depth at its default value of 100%.
  • Now as you play notes, you can use the modwheel to morph between vowel sounds.
• If the output level seems low, you can boost it by increasing the Master Amp and/or Volume knobs. (And a further boost, should you need one, is available if you load a Compressor module in the effects rack and adjust the Amount knob.)