Logic Pro Alchemy source filter use tips

Alchemy provides multiple filter types at different positions in the signal path. You can use filters at the source level, and the main filters, and you can also insert filters in the effects section. The positioning can have a significant bearing on the sound produced and can also impact on the processing resources required. Depending on currently available resources, you may need to pay close attention to envelope settings, the number of voices, and other parameters to achieve the sonic result you are chasing.

Source-level filtering provides the most precision and potentially the greatest sonic impact on your sound. The downside is that source-level filtering requires more processing resources. Processing is per voice.
Use of the main filters is more CPU-efficient and can have significant sonic impact. Processing is per voice.
Effects section filters process the entire signal, rather than each voice independently. Filtering at this stage of the signal path is often used to refine the overall sound or to provide a performance control variation.

Use an FM filter as a sound source

The FM filter produces a sine wave that is modulated by your source signal. Because the FM process adds harmonics to the sound, the more complex the sound you feed into the filter (and the louder it is) the more quickly the sound is distorted. FM in Alchemy is great for aggressive sounds, but is also useful for basses and other sounds.

Unlike dedicated FM synths, Alchemy does not have preconfigured algorithms or a modulation matrix set up for FM synthesis. It does, however, offer the option to run a huge number of “operators” (FM filters) in various series and parallel configurations. FM in Alchemy also has a sonic character that’s different from classic FM synths. This means following the approach outlined in the steps below is not always the best option in Alchemy if you want to recreate classic digital FM sounds. Such sounds are often more easily achieved by other means, such as with additive synthesis or resynthesis. FM in Alchemy is more like working with FM on analog synths where you modulate oscillator frequency rather than phase.

In Logic Pro X, from the Name bar, click the File button and choose Initialize Preset from the pop-up menu to reset all Alchemy parameters to default settings.
Switch to advanced view, then click the A button to show source A parameters.
Use a sine or triangle wave as your source sound.
Click the source A filter On button to enable the filter, then choose FM from the Filter type pop-up menu.
Control-click the Frequency knob, and choose Envelope Follower > Source A.
The filter is assigned to track keyboard pitch. By default, the centered knob at 523Hz provides a medium pitched sound that works well. If you want to change the octave, multiply or divide by two, and round to the nearest whole number that sounds best. For example, set the Frequency knob at 262Hz for one octave lower.
Adjust the modulation Depth on the filter to increase the impact the source signal has on the sine wave generated by the FM filter, and listen to the results. For more grit, try adjusting the Feedback control, which allows the filter output to apply modulation to itself.
FM in Alchemy requires experimentation to develop more complex sounds. Here are a few things to try:
- Use other types of VA oscillators or samples as your modulation source.
- Run multiple FM filters in series or parallel to see what best meets your needs. When doing so, resist high initial modulation and feedback depths so you can get a feel for the degree of control you have in shaping the overall sound.
- Use independent envelopes for the frequency and volume of your source (or on FM filters earlier in the signal path) to hear the results this provides.
Important: Due to technical requirements, FM is often best done at the source filter level. As you progress through the signal path, gain increases (and therefore FM) become increasingly heavily modulated and distorted. You will find that it is easier to work with FM at the source level than as a master filter or effect.

Use a comb filter as a sound source

When making comb filters your primary sound source, you may find that longer master envelope release settings are required for a natural feel when playing. This results in more overlapping notes, higher polyphony, and therefore more CPU overhead. Because of this, you may need to carefully adjust envelope release times and reduce the maximum number of voices in the Master section.

In Logic Pro X, from the Name bar, click the File button and choose Initialize Preset from the pop-up menu to reset all Alchemy parameters to default settings.
Switch to advanced view, then click the A button to show source A parameters.
Click the source A filter On button to enable the filter, then choose Comb PM from the Filter type pop-up menu.
Control-click the Frequency knob, and choose Envelope Follower > Source A.
The filter is assigned to track keyboard pitch. By default, the centered knob at 523Hz will provide a medium pitched sound that works well. If you want to change the octave, multiply or divide by two, and round to the nearest whole number that sounds best. For example, set the Frequency knob at 262Hz for one octave lower.
Control-click the Volume knob for source A (choose the lowest feasible level), and assign a New AHDSR from the menu.
Set up an envelope for your impulse signal to excite the comb filter. You can choose any impulse type, from VA noise to resynthesized samples. The aggressive nature of FM also makes this a good choice of impulse for comb filters.
The impulse requires its own envelope, separate from the master or any envelope you have controlling the comb. The best settings for the envelope depend on the needs of the sound, but a good rule of thumb is to start with zero attack, zero hold, a very short decay, zero sustain, and zero release. This provides a quick spike that starts comb movement and allows the remainder of sound generation be handled by the comb itself.
Tip: The chosen impulse can have a large impact on the tone so it is worthwhile experimenting with different sound sources. One approach is to import a sample with a strong initial attack using the Additive import method, then use the Additive Harmonic effect knobs to adjust the tone. These controls plus comb filtering can provide numerous fast and easy adjustments, letting you dramatically alter the perceived hardness, material, and tone of your modeled sound. You can also import a drum loop and set it to sustain with Continuous Loop mode. Because drum loops typically contain short bursts of sound that vary in tone, they work well with comb filters.
Use the Damp control to reduce ringing or other artifacts in the sound, if required.

Helpful?

Logic Pro X User Guide

Logic Pro Alchemy source filter use tips

Use an FM filter as a sound source

Use a comb filter as a sound source