Legato Phrasing

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If you’ve played the previous examples on the G2 keyboard, you’ve probably noticed that playing a legato phrase is unsatisfactory: the pitch jumps from note to note in an electronic, not acoustic, fashion.

The reason is that most wind instruments change pitch by opening and closing toneholes, or by depressing valves that select different sections of pipe. These actions have a short but measurable transition time, when the air stabilizes and forms a new vibration.

Adding portamento won’t do the job. But we can borrow a technique used by the Yamaha VL1. It has two pipes, not one. The pipes are arranged in parallel. They’re fed by the same source, and their outputs are summed in a crossfader that selects one of the pipes.

A switching system alternates back and forth between the pipes each time a new note is selected. One pipe is tuned the “old” note, while the other pipe is tuned to the “new” note. The crossfader is swept from the “old” note to the “new” note whenever a new note is chosen. Let’s see what happens when we play a short phrase using the notes C, D, E, and F:

1. When we press C, pipe 1 is tuned to C, and the crossfader selects pipe 1. The note begins.
2. When we press D, pipe 1 remains tuned to C. Pipe 2 is tuned to D, and the crossfader sweeps from pipe 1 to pipe 2. The speed of the crossfader sweep can be programmed (typically between 5 and 50 milliseconds).
3. When we press E, pipe 2 remains tuned to D. Now, pipe 1 is tuned to E, and the crossfader sweeps from pipe 2 to pipe 1.
4. When we press F, pipe 1 remains tuned to E. Now, pipe 2 is tuned to F, and the crossfader sweeps from pipe 1 to pipe 2.

The effect is a smooth legato transition, requiring only two delays, a crossfader, and an alternating switching system. On the G2, this can be done with ease. The patch below demonstrates one method.

What’s new?

The bottom right side of the patch contains the new pipe. There are now two delays instead of one. They’re fed by the same source, and are mixed together with a crossfader. The crossfader is set to linear interpolation, and initially favors Delay 1.

The bottom center of the patch contains the new control portion. This is a switching system that alternates from one pipe to the other every time a new note is pressed. It has three outputs:

1. The pitch of pipe 1 (Delay 1).
2. The pitch of pipe 2 (Delay 2).
3. A logic signal which tells the crossfader which pipe to use.

How does it work?

Let’s see how this works. When the patch is loaded, the Q output of the D-style flip-flop is off, and the Q-bar (not Q) output is on. This means that the crossfader is selecting pipe one. It also means that the upper Track/Hold module is turned on, letting the pitch through to Delay 1. The lower Track/Hold module is turned off, preventing Delay 2’s pitch from changing.

When the first key is depressed, what happens?

1. The D-style flip-flop changes state. Now, the Q output is on, and the crossfader will begin fading from Delay 1 to Delay 2. Its speed is controlled by the Glide module.
2. The upper Track/Hold module is turned off, locking Delay 1’s pitch.
3. The lower Track/Hold module is turned on, passing the new key’s pitch to Delay 2.

The effect is that the old note’s delay, Delay 1, has its pitch locked at the old note, while the new note’s delay, Delay 2, now tracks the keyboard. And the pipe’s crossfader quickly shifts from Delay 1 to Delay 2.

When the next key is depressed, the delay’s switch places: Delay 2 is locked at the old note, while Delay 1 begins to track the new note. And the crossfader shifts from Delay 2 to Delay 1.

Notice that the keyboard pitch goes through a very short delay before reaching the Track/Hold modules. This is to ensure that the Track/Hold modules lock the old pitch, not the new one (because the new one is slightly delayed).