Tuning the Pipe

 

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Waveguide models tend to go flat, especially when playing higher notes.The Yamaha VL1 compensated for this by having a piecewise-linear tuning table.Certain notes could be tuned, and the instrument would interpolate the remaining notes.

 

We can do this on the G2, also.The SeqCtr module is ideal for the purpose.Itís a 16-stage table, where an input signal (the Ctr input) determines which stage is being addressed.Sliders control the output level at each stage.The patch below uses two SeqCtr modules to tune the pipe at every fourth note between C2 and C7.One is used for coarse tuning (by semitone), and the other is used for fine tuning (+/- Ĺ semitone).This matches the 5-octave range of a typical organ keyboard.

 

 

 

 

Notice that the keyboard pitch is used to address the SeqCtr tables.Then, the output of the SeqCtrs table are summed and used to adjust the pitch of the delay line.

The keyboard pitch needs to be adjusted so that the bottom note being tuned has the value 0 (to address stage 1 on the SeqCtrs).In this example, the desired range is from C2 to C7.Since C2 has a note number of -28 (remember that on a G2, the E4 key is note number 0), weíll begin by adding 28 to the keyboard pitch.

 

So, when we press C2, we can adjust the pipeís pitch by moving slider #1 on the SeqCtr modules.The coarse-tuning SeqCtr adjusts up and down by semitone.The output of the fine-tuning SeqCtr is attenuated, and adjusts up or down a total of Ĺ semitone.

 

What about other notes?A SeqCtr module moves to the next stage when the Ctr input is increased by 4.This means that when we press E2 (four notes above C2), we can adjust the pipeís pitch by moving slider #2 on the SeqCtr modules.

 

What about D2, halfway between C2 and E2?If we set the XFade controls to 100%, pressing D2 (or C#2 or D#2) will properly average the outputs of sliders #1 and #2.

 

What is the range of this technique?With 16 steps in the module, addressed every four notes, the range turns out to be exactly five octaves.But which five octaves?That depends on our starting note.In this example, we chose C2.For a bass instrument, C1 might be a better choice, and can be accomplished by adding 40 to the keyboardís pitch instead of 28.

 

If we choose C2 as the bottom note, the table below shows which keys line up with the SeqCtr tuning sliders:

 

Key

SeqCtr Stage

C2

1

E2

2

G#2

3

C3

4

E3

5

G#3

6

C4

7

E4

8

G#4

9

C5

10

E5

11

G#5

12

C6

13

E6

14

G#6

15

C7

16

 

 

 

Tuning Every Single Note

 

Sometimes, it may not be good enough to tune every fourth note.So, what can be done when every single note in an instrumentís range needs to be tuned?Can this be done using the same technique?Yes, but it requires more work.The patch below tunes every individual note between B1 and G#6, and contains both coarse- and fine-tuning controls for each note.

 

 

 

 

Fortunately, itís not hard to figure out which slider goes with which key.Each SeqCtr module has a light above slider.Notice that as you play up the keyboard, the lights follow the note youíre playing.

 

This patch uses the same basic technique as the top one.But notice that between the SeqCtrs, steps 1 and 16 arenít used.This is because SeqCtrs canít be programmed to interpolate from one to another.When theyíre addressed outside of their range, they simply ďparkĒ, which sets their outputs to zero.

 

So when interpolating between modules, such as from C#3 to D3, what happens?The C#3 slider, step 15 on the left-most SeqCtr, interpolates to step 16, which is zero.The D3 slider, step 2 on the next SeqCtr, interpolates from step 1, which is zero.Since the outputs of both SeqCtrs are summed together, the net effect is a proper interpolation between notes.It works, but it means that we only get 14 or 15 notes out of a SeqCtr, instead of the full 16.

 

Itís an ugly solution, isnít it?Letís petition Clavia for a 64-step SeqCtr module, or a way to draw a curve on a screen.

 

Fortunately, the top tuning method is usually sufficient.