Once you have accessed the Source Edit page, clicking the SPECTRAL button at the top of the right-hand half of the page will bring Alchemy’s Spectral Editor into view.

Overview

The Spectral Editor serves two purposes. First, it allows graphical editing of spectral resynthesis data. And second, it allows you to design sounds from the ground up by working with simple ‘paint’ tools directly on the ‘canvas’ of the the graphical display.

Spectral data is displayed in the editor according to the following principles:

• Time (in sec) is represented along the x axis (from left to right).
• Frequency (in Hz) is represented along the y axis (from bottom to top).
• Amplitude is represented by brightness, using shades of blue. The full range, from silent (black) through loudest (white) looks like this:

Note that accurate resynthesis requires a much finer frequency resolution than the spectral display can accommodate. Therefore the frequency information depicted in the display is a somewhat coarse representation of the underlying data. Editing and creating data graphically is performed at the resolution of the display. This means, for instance, that you cannot paint conventional melodies and chords consisting of precise notes.

Spectral editor controls

(Click to view full size.)

• Click the FILE button to access a pop-up menu with the following commands:
  • Import Image — Opens a dialog in which you can select a file in PNG fomat to be placed as an image on the spectral canvas. The imported image is placed at the far left of the canvas. The height of the image is scaled to fit the entire vertical range of the canvas, and the width of the image is scaled by the same factor as the height (so the proportions of the original image remain intact). The imported image’s color information is discarded, and its brightness information is mapped to the shades-of-blue amplitude scale described above. If the newly placed image does not extend fully to the right-hand edge of the canvas, then existing data that lies beyond the right edge of the newly placed image remains in place.

    Images with a height of 256 lines will result in a 1:1 mapping of pixels to spectral bins. The spectral editor actually displays the image as 381 lines, so when editing within Alchemy there will be some blurring between bins.

  • Import Image to Brush — Opens a dialog in which can select a file in PNG format to be used as a brush for painting on Alchemy’s spectral canvas. Unlike importing an image directly onto the canvas, importing it as a brush preserves the original dimensions of the image and gives you full control over the position at which the image is placed. (As with any brush, you can ‘print’ an image of the imported brush by clicking or paint strokes with it by dragging.)
  • Undo — Reverses the last change made to the spectral data.
  • Clear — Deletes all spectral data from the source, leaving only silence (solid black image).
• SELECT and BRUSH buttons — When the editor is in SELECT mode, clicking and dragging across the spectral canvas defines a rectangular selection. If you then switch to BRUSH mode, the selection you’ve just defined can immediately be used as a brush shape, which remains available until you select a different brush shape.
• The Shape field offers a choice of several pre-defined brush shapes, each with a descriptive name.
• The Colour knob adjusts the amplitude scaling of the brush. White brush pixels paint white on the canvas when Colour is 100%, medium blue on the canvas when Colour is 50%, and black on the canvas when Colour is 0%. Brush pixels representing lower amplitude values are scaled accordingly; for example, medium blue brush pixels paint medium blue on the canvas when Colour is 100%, dark blue on the canvas when Colour is 50%, and black on the canvas when Colour is 0%.
  
• The Opacity knob allows for transparency effects. When Opacity is 100%, the paint modes behave as described below (see ‘Paint mode buttons’). When Opacity is 50%, the pixel values that result from painting in any mode are halfway between the pixel values in the existing image and the pixel values that would result from painting with full Opacity. (Note that an image imported directly to the canvas will always have full Opacity; on the other hand an image imported as a brush can be used to paint with any degree of Opacity.)
• The Paint mode buttons determine how the brush interacts with the existing canvas image.
  • In SET mode, each pixel on the canvas is set identically to the corresponding brush pixel. In this mode, painting with black replaces the existing image with silence.
  • In ADD mode, the brush pixel values are added to the existing canvas pixel values. In this mode, painting with black leaves the existing image unchanged, while painting ‘multiple coats’ of blue results in higher and higher amplitudes the more coats you paint.
  • In MUL mode, the brush pixel values are multipled with the existing canvas pixel values. In this mode, painting with black on an image of any color, and painting on black with paint of any color, both result in black. You can use a black brush in MUL mode as an eraser, and you can use a brightly-colored brush in MUL mode to boost the portions of an image that already produce sound, without disturbing the portions that are silent.
  • Finally, in DEL mode, the brush pixel values are subtracted from the existing canvas pixel values. In this mode, a bright white brush works like an eraser.
    

Spectral canvas

Once you are familiar with the brush modes, the relation between colour and amplitude, and the distribution of frequencies from the bottom to the top of the canvas, working in the spectral editor’s graphical display is an intuitive process. Here are some useful techniques and related information.

• The time (in sec) and the frequency (in Hz) of the brush (or selection cursor) position are reported in Alchemy’s parameter value display. If data is present at, say, the 2500 Hz position, this means that the output of the spectral element will include a 2500 Hz component when C3 is played (or when keytracking is off and any note is played).
• To constrain painting vertically, hold Shift while painting.
• To constrain painting horizontally, hold Control (Windows) or Command (Mac) while painting.
• Warp markers are superimposed on the canvas and can be moved freely by dragging their handles. To create or delete warp markers, or re-assign the loop start and end markers, switch to the main Source edit view by clicking the MAIN button at the top of the editor.
• Beginning in version 1.12, a Play Cursor scrolls across the display, tracking the progress of the most recently played note.

Example: Modifying a drum loop

• Initialize Alchemy by choosing the ‘Clear’ command in the Title bar’s FILE menu.
• Import (into Source A) the factory sample ‘Loops’ > ‘PercussiveLoops’ > ‘DjembeLoop2-4bts’. Be sure to set the import mode to SPECTRAL. (See the Import page for more details of this process.)
• The imported image should look as follows. In this illustration, a superimposed series of arrows marks certain drum hits that we will now modify.

(Click to enlarge.)

• Select the brush shape ‘Transient’, which is designed for creating or boosting attack transients. We’ll use this tool to add ‘punch’ to the four drum hits marked above. Set the colour to light blue (Colour knob turned to approximately 75%), and set the brush mode to MUL. Carefully align the brush so that its bright left edge coincides with the peaks marked above, and click one or more times in each of these positions, until the result looks something like the following. (Play and hold C3 on your MIDI controller to hear the effect of these edits.)

(Click to enlarge.)

• Let’s make some additional changes to the end of the loop.
  • Scroll the spectral canvas to the right until the final beat is in view. (All of the actions described below are summarized in the illustration that follows.)
  • With the ‘Transient’ brush still selected, and the brush mode still set to MUL, reduce the Colour value all the way to black (Colour knob turned fully left). Then align the brush with the position one sixteenth note after the final beat; click at this position, and drag to the right to erase all the spectral data from this position to the end. (Play and hold C3 again on your MIDI controller to confirm that this produces a silent region at the end of the loop.)
  • Next, switch to the SELECT tool and select the first half of a medium-loud drum hit. Switch back to the brush tool, turn the Colour knob fully right, and set the brush mode to SET. You can now paint using the selected image as a brush. Click four adjacent positions at the end of the loop to produce a ‘roll’ effect. (Play and hold C3 once more on your MIDI controller to hear the final result.)

• These last three steps are summarized, alongside the results they produce, in the following illustration.

(Click to enlarge.)