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Using the nona-layer to create a drawbar organ on the G1


BrettM

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It may not be as instantly accessible as the drawbar organ on the P1, but it is possible to recreate a complete drawbar organ on the G1; going way beyond the dozen or so PCM organ presets. To do this, we need to utilize the G1's sound creation resources, especially the sampler and the nona-layer1, and go back to first principles.

 

The basic building block of a drawbar tone is a clean sine wave. Unfortunately the only PCM sine preset, P268, has vibrato, so we have to use the sampler to extract a clean sine from the solo synth. Alternatively the recorder, P209, with cutoff zeroed, could be used; but if you want complete authenticity, sample a sine wave instead. Flutes also provide good approximations to sine waves; but unlike P209, P208 contains considerably more modulation. I usually sample note C5, taking care to set the looping point to minimize pops.

 

Then use the mixer to assign the clean sine to all nine parts of the nona-layer. Next comes the most important bit, playing the appropriate note at step one of parts 8 to 16 of the step sequencer to give the appropriate harmonic for each drawbar. This is done using step sequencer step edit.

 

With middle C, C4, as the "fundamental"2, the nine parts of the step sequencer should be configured as follows.

 

Step sequencer part | Note to play at step one | Drawbar

            8                 |                C3                |    16'

            9                 |                G4                |     5 1/3'

           10                |                C4                |     8'

           11                |                C5                |     4'

           12                |                G5                |     2 2/3'

           13                |                C6                |     2'

           14                |                E6                |     1 3/5'

           15                |                G6                |     1 1/3'

           16                |                C7                |     1'     

 

Take care to only change step one of each track and make sure all the velocities are identical. Also ensure that all of the tied steps in the nona-layer are intact. It is evident from the above table that the harmonics span four octaves; which is why we sampled C5 instead of C4, even though C4 is the "fundamental". The sampler will only pitch shift +/- 2 octaves. Save this as a user wave tone with original key set to C4.

 

Now it's time to create a drawbar registration, say 88 5324 588. This can be done in the mixer by using the sliders to set the volume of each part. Although the G1 has 128 distinct volume levels, real drawbars only have eight stops; so to be truly authentic, we need to adjust the volumes in increments of 16. (On the other hand, why not experiment with fractional stops?) To create 88 5324 588, we would set the volume of part 8 to 127, part 9 to 127, part 10 to 80, part 11 to 48, part 12 to 32, part 13 to 64, part 14 to 80 and parts 15 and 16 to 127.

 

Now start the step sequencer. Voila, you have just created a drawbar organ tone! Record a few beats of this in the sampler, taking care to avoid recording through the step sequence restart. Again, edit the loop points of the sample to minimize pops.

 

Now we've got something playable, but we're still not quite done. Although we have created the desired registration, a real drawbar organ has a number of additional characteristics, like note-on percussion and a Leslie speaker. While the Leslie can obviously be implemented by applying the rotary speaker DSP, the best way to implement percussion is in performance mode.

 

Create a new performance with the above sampled drawbar registration in zone 1. Now set zones 2 and 3 to P280, Sequenced Sine, which gives a nice quick pulse. Zone 2 implements the second harmonic percussion, so set the octave shift parameter for zone 2 to +1. Zone 3 implements the third harmonic percussion, which is 19 semitones above the "fundamental", so set the octave shift parameter for zone 3 to +1 and the transpose parameter to +7. The percussion should not overpower the main tone, so set the volumes of zones 2 and 3 to about 30. Switching zones 2 or 3 on and off switches the relevant percussion on and off as required.

 

While we're at it why not set zone 4 to the original sine wave? Then if we're using a drawbar registration of 88 8000 000, say, and want to play 88 8000 005 instead, all we need to do is activate zone 4, set its octave shift to +2 and volume to 80 without having to go though the full tone creation process.

 

To facilitate realtime play, zones 2 and 3 can be toggled in the mixer, or via the assignable knobs. The other two assignable knobs can be configured to operate the rotary speaker – on/off, fast/slow. Vibrato is achieved via the standard modulation wheel.

 

Now we're really ready to play. If I remember my combinatorics correctly a standard drawbar organ has 99 = 387,420,489 possible registrations. The G1 drawbar, with 128 volume levels to choose from, has 1289 = 9,223,372,036,854,780,000 registrations. That's over nine billion billion possibilities.

 

Limitations

  • Can't change the drawbars on the fly, although you could fill the sampler with up to 50 drawbar registrations and switch between them in real time.

  • Drawbar organ purists may point out that the percussion should only trigger after all keys are up. With a bit more effort this effect can be implemented via solo synth legato mode.

Other possibilities

  • Instead of using the nona-layer to create the basic drawbar tone, the appropriate nine notes at their required volumes could be layered directly into the sampler via overdubbing.

  • Many popular drawbar registrations are of the form 88 8842 000, so an LPF ought to be able to recreate them subtractively from the full drawbar 88 8888 888, P140, although you won't know exactly what you're getting. Filtering the other PCM organs also offers interesting possibilities.

  • Instead of using a clean sine as the basic building block, why not try a completely different tone entirely; even something from the solo synth – subtractive synthesis meets additive synthesis! They certainly don't cancel each other out.

 

1. I've described how to set up the nona-layer in the General Discussion area.

2. This is usage of the term fundamental as found in discussions of drawbar organs, as opposed to the fundamental frequency of the overall tone which is given by the first drawbar.

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There must be a easier way, and there is. After much experimenting I've realised that we can use nine splits across two user waves to hold the basic tone for each drawbar and just edit the volumes of each split to create the desired registration. The only downside is that we don't get to play with the sliders. I've uploaded two user waves and a performance that does this in the download section.

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