A Generic Brass Horn

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Bugles aren’t very useful, since they can only play a few pitches. We need a horn with a variable-length bore. Real brass instruments use two kinds of mechanisms to change the bore size: slides (trombones) and valves (just about everything else).

But those mechanisms are more complicated than they first appear. So before we imitate the mechanism of a real instrument, we’ll create a simpler, synthetic one. One that’s similar to the Yamaha VL1.

Remember that the pitches of brass instruments are harmonics of the pipe length. That is, the lips vibrate at the pitch we hear, while the pipe itself is longer, perhaps quite a bit longer. So, to build a simple brass instrument, we can follow these steps:

• Track the pitch of the lip filter with the keyboard. This will be the pitch we hear.
• Track the length of the bore delay with the keyboard, too. But lower that length by one or two octaves, so that the lip filter is playing a harmonic of the bore delay’s length.

The patch below does this. Notice that the patch now tracks the keyboard.

What’s changed?

• The lip filter now tracks the keyboard, at the keyboard’s fundamental pitch. You can make the horn squeal or fall off by raising or lowering the “Lip Pitch” knob.

• The bore delay now tracks the keyboard, too, but two octaves lower (-24 semitones), and can be changed via the “Bore Pitch” knob. Try changing this to minus 12, or minus 36. Notice that the lower you make it, the longer the attack time is. That’s because the bore is longer, and it takes more time for the reflections to build up and create a tone.

• A little bit of pitch glide has been added to both the lip and bore pitch controllers. This is to minimize electronic-sounding jumps.

• Vibrato is created by modifying the pitch of the lip filter, but not the length of the bore. This is how most brass instruments create vibrato. Only the trombone can create vibrato by varying the bore length.

It’s not like a real horn, is it?

No, it’s not. It’s kind of like a trombone whose slide length can vary from 1 foot long to 30 feet long. But it’s still an interesting experiment.

An improvement

Before we continue on to a more realistic mechanism, let’s make an improvement to this one. The pitch on this patch seems to slide around a lot. If we can paste the legato pipe-switching logic from the other models onto this, perhaps we can get more realistic note-to-note transitions.

Below is a patch that does this. The big change is in the bore. In place of the single delay, there are now two delays with a crossfader. Also, the pipe-switching logic from previous models has been added. The lip filter is unchanged. Notice that note-to-note transitions sound more realistic than before. Also, we’ve routed vibrato depth to the mod wheel morph group.