Brass horns come in many types. Popular horns include trumpets, French horns, trombones, and tubas. Less-common horns include cornets, baritones, bugles, and flugelhorns.
The simplest horn is a bugle. It’s simply a flared pipe and a mouthpiece. If you disconnect the mouthpiece from the horn while a bugler is playing a note, you’ll hear a buzzing tone coming from the mouthpiece. No big surprise there. The surprising thing is that the pitch of the buzzing tone is very near the pitch of the original note.
It’s the player’s lips that are buzzing. This vibration is amplified and shaped by the flared pipe into the tone we hear from the bell.
A bugle can play only a few different pitches. A standard bugle is tuned in G, and can play (in ascending order) D, G, B, D, F, and G. These pitches correspond to the 3rd through 8th harmonics of the pipe length. Due to the shape of the flared bell and the mouthpiece, it’s more complicated than that. But it’s good enough for our purposes.
Through practice, the bugler can adjust his embouchure so that his lips vibrate at the correct pitch at the beginning of a note. One of the marks of a beginning bugler is sloppy attacks because he can’t find the correct embouchure quickly.
Our first brass model
Our first brass model is a bugle. The patch is below. Although it’s triggered from the keyboard, the keyboard does not control the pitch of the instrument. The pitch is controlled by the “Lip Pitch” knob, which has been brought out to the front panel.
How does it work?
This bugle consists of four basic parts:
Air source: Nothing special here. This is a standard envelope generator that creates a voltage which represents the air pressure going into the bugle.
Lip driver: This driver is unlike anything we’ve used before, and is the key to the instrument. This is a G2 version of the lip driver contained in Perry Cook’s STK synthesizer development software. Unlike the jet driver we’ve been using, this driver actually oscillates. The difference of the incoming air and the returning air drives a resonant filter that represents the player’s lips. The output of the filter then determines what air is returned to the pipe: the incoming air or the reflected air. A highpass filter prevents DC buildup. In this patch, the filters do not track the keyboard. They’re tuned to 523 Hz, or C5.
Pipe: This is just a tuned delay line with a lowpass filter, like we used in the blown pipe. A flared bell would be more realistic, but there’s no easy way to create one on the G2, so this will have to suffice. The delay does not track the keyboard, and is tuned to 261 Hz, or C4 (one octave below the lip driver).
EQ: This is just a wide bandpass filter that mimics the frequency response of a flared bell.
Playing the bugle
To play the patch, press a note on the keyboard. Every note will play the same pitch. When the Lip Pitch knob is set to zero, the bugle will play the pipe’s second harmonic, which is C5 in this model. Moving the Lip Pitch knob creates that recognizable brassy squealing sound, until the pitch of the lip filter matches one of the pipe’s harmonics.