Explore Alchemy’s oscillators, envelopes, modulation mapping and effects to create a classic house organ patch in Logic Pro X.
In this month’s Logic workshop we look at how to remake the classic dance-music organ bass patch using Alchemy, with particular focus on its virtual analogue waveforms and modulation matrix. Organ bass sounds like the classic Korg M1 preset are back in vogue. If you missed this sound the first time round, or need a quick refresher, check out records from the ‘90s such as ‘Show Me Love’ by Robin S.
In a new Logic project, create a new software instrument track and on it add an instance of Alchemy. Alchemy loads up with a default preset that already contains myriad effects and modulation assignments. From the File menu, choose the Clear option. This resets Alchemy, removing all effects and modulation assignments.
First, let’s set up the four oscillators to give us that distinctive organ bass sound. Go to the Advanced page in Alchemy and note that the left-hand side of the Global tab displays a simplified view of the four oscillators that make up an Alchemy patch. Go to oscillator A, located in the sources area, and click on the combo box that reads ‘Saw’. From the drop-down menu, navigate to the Load VA section. The submenu displays a range of typical virtual analogue waveforms, as well as some interesting variations on them. Navigate to the Sine section and choose the ‘Sine - Power4’ waveform (see Screen 1). This particular waveform sounds like a mellow version of a square wave with plenty of upper harmonics, which is perfect for building our patch from.
Next, switch on oscillators B, C and D by clicking on them, and set each of them to the ‘Sine - Power4’ waveform. The classic organ sound is achieved by tuning the four oscillators to specific pitches. Go to oscillator A and set its Tune parameter to -24 (down two octaves), then set the Tune parameter of oscillators B and C to -12 (down one octave) and, lastly, set the Tune of oscillator D to +7 (up a fifth). We can thicken the sound by detuning some oscillators and also panning them slightly left and right. To do the former, click the ‘B’ located underneath ‘Global’ in the top left of Alchemy to open the detailed view. Go to the Fine parameter and set it to -7 cents, then go to oscillator C’s detailed view and set its Fine parameter to +7 cents. Detuning in this way creates a mild chorusing effect, which can be exaggerated by increasing the fine-tune offsets. Return to the Global tab and set the Pan control for oscillators B and C a little left and right to give some stereo width.
Now let’s set up our amplifier envelope so that the bass sound has a snappy, short, decaying sound. From the modulation area click on the AHDSR envelope. This is assigned by default to control the Amplifier stage of Alchemy. To get the desired envelope, set both the Decay and Release to 0.86 seconds. In Alchemy, you can specify the curve of the envelope to get different decay characteristics. In the envelope graph, click and drag the decay portion up and down to change the curve of the decay stage of the envelope from linear to other shapes. Set this curve to taste by auditioning the sound in the lower registers.
Next let’s turn our attention to the filter section. On the Global tab of the Advanced page, go to the Filter section and set the Cutoff knob of filter 1 to 16Hz, its minimum value. Let’s now modulate Filter 1 with an additional envelope. The modulation area is displayed in the centre row of Alchemy’s plug-in GUI. On the left-hand side is the Modulation Rack, which will update dynamically to display the modulation assignments belonging to the currently selected parameter. The currently selected parameter is typically the control you clicked last, and if it’s a knob, it will be highlight in blue. To the right of the modulation rack are the modulation controls for each type. This area helpfully switches to display the modulator you assigned last.
Select the filter 1 Cutoff knob by clicking on it. It will turn blue, and you should see it displayed as the Target in the Modulation Rack. On the rack, click in the first empty modulation slot, and from the drop-down menu go to AHDSR Env and select New AHDSR (see Screen 2). Alchemy now creates a second envelope and assigns it to the filter cutoff ready for you to tweak. Move across to the AHDSR area and set the envelope’s Decay time to between 0.4 to 0.8 seconds. Shorter times will give you a snappier bass sound, whereas longer times allow each note to ring more. Set the same time for the Release stage. Now move to the Attack stage, and experiment with times between 0 and 0.03s. Setting the Attack to 0 gives the bass sound a strong, almost clicky onset, whereas an attack time of 0.03s softens the front of the waveform, which may help to leave room for kick drum transients to poke through your mix.
We have now completed the main aspects of the organ bass. Try auditioning your patch on a keyboard to hear the result. If you want to go further, it is possible to use the velocity of a note to control the amount that the envelope modulates the filter. This will create a more expressive version of the patch. To do this you need to remove the default mapping of velocity to master volume, so as to ensure the bass sound remains at a consistent level. Click the Master Volume knob to display its modulation assignments in the Modulation Rack. The second assignment is Velocity: click the On button to turn this off so that it is no longer illuminated. Now let’s assign the velocity parameter to control your filter envelope’s depth. Click on the filter Cutoff knob, and from the Modulation Rack, set the Depth of the AHDSR2 envelope to zero. This can be achieved quickly by holding down the Option key and clicking on the Depth control. To use the velocity of a note to control the amount the envelope modulates the filter, we need to modulate the envelope’s Depth knob with the velocity parameter. Ctrl-click on the AHDSR2 Depth knob, and from the pop-up menu go to Add Modulation / Note Property / Velocity (see Screen 3). The Depth control now sets the range by which the velocity will modulate the filter. Begin by cranking the Depth control up to its maximum value, and play some notes on your keyboard at different velocities to see how the patch responds. It’s worth taking some time to experiment with the Velocity modulation’s Depth control to achieve a result that you like.
If simply adjusting the amount of depth didn’t quite achieve the result you were after, fear not. Alchemy has extensive options for tweaking how modulators respond across their value range. Let’s adjust Alchemy’s response curve to customise how your keyboard’s velocity will change the filter envelope’s depth. Click on the dash by the Velocity modulation assignment, and from the drop-down menu choose 1, which is Alchemy’s default Modulation Map (see Screen 4). The Modulation Map is automatically displayed on the right of the Modulation Rack. Open the ‘Modmap‘ tab if it’s not already visible. You can set it so that lower velocities open the filter more by raising the Modulation Map’s lower limit; do this by clicking on the left-hand node and dragging it up higher. To make the filter open less at maximum velocity, decrease the upper limit by clicking on the right-hand node and dragging it down. You can further tailor the response between the lower and upper limits by clicking on the diagonal line between them and dragging it up or down to alter the curve. Make these changes whilst playing the patch from your keyboard until it feels suitably expressive.
To finish off the patch, let’s add some of Alchemy’s excellent insert effects. Go to the Effects area at bottom left and click on the first insert slot. Add the Acoustic Reverb effect and set its mix parameter to 9 percent. Next, brighten the bass sound slightly by adding the Three Band EQ to insert slot two and making a small boost at 2kHz. Now add the Delay effect to insert slot three, setting the left side to an eighth note and the right to a 16th note with the Mix set around 23 percent. Lastly, finish the patch off with the Phat Compressor and Distortion effects to add some weight and grit to the sound.