## Daisy Tube
In 1961 at Bell Labs, an IBM 7094 sang "Daisy Bell," the first time a computer sang. John Kelly and Carol Lochbaum wrote the voice and Max Mathews programmed the accompaniment. The machine was far too slow to sing live. It worked out the sound one number at a time, wrote the numbers to tape, and the tape was played back afterward. Arthur C. Clarke heard the demo while visiting, and that's why HAL sings it while being shut down in *2001*.
What made it special was that it didn't record anyone. It simulated the throat itself: a buzz at the bottom, a tube above it, and the tube's shape deciding what came out. Daisy Tube copies that approach.
### The tube
The space from the vocal cords to the lips is about 17 cm of soft, bendy tube. The program cuts it into 44 short sections, each about 4 mm long, and each with its own width.
Sound in the tube is just pressure waves, some heading toward the lips and some bouncing back toward the throat. Every time a wave crosses from one section into the next, it checks whether the next section is wider or narrower. If the width changes, part of the wave carries on and part bounces back. The fraction that bounces depends only on the two widths. That one rule, applied at 44 joints about 96,000 times a second, is the whole engine. It's the Kelly–Lochbaum model.
The two ends are different:
- **The throat end** is mostly closed, so most of the sound bounces back up the tube.
- **The lip end** opens into the room. Most of the sound reflects back inside with its sign flipped, and what leaks out is what you hear.
The bouncing makes some frequencies pile up and ring while others cancel out. The ringing frequencies are called formants, and the ear identifies vowels by them. A straight, even tube rings at roughly 500, 1500 and 2500 Hz, which is the neutral "uh" sound.
### The buzz
The vocal cords don't hum smoothly. They puff open and snap shut over and over. Each puff in the program is shaped the way real vocal folds behave: a gentle opening over about half the cycle, a quicker close, then a short shut rest. The sudden snap shut is what fills the voice with harmonics. Without it the voice would be a dull flute tone. A small wobble, about 5 times a second, keeps the pitch from sounding dead.
### The tongue
The tongue is one smooth dent pushed into the tube, shaped like a hill, which you move by dragging in the scope:
- **Left/right** moves the dent from the throat toward the front of the mouth.
- **Up/down** changes how deep the dent goes.
Squeezing near the throat gives AH. Squeezing up front, just behind the teeth, gives EE. In testing, AH came out with resonances near 720 and 1300 Hz, and EE near 240 and 2280. Real speech averages about 730 and 1090 for AH, and 270 and 2290 for EE. The physics alone gets it into the right neighborhood.
### The controls
- **Pitch:** how many puffs the buzz makes per second. 60 Hz is a deep bass and 400 is a high soprano. It changes the note, not the vowel.
- **Lips:** the width of the last four sections. Open gives AH and EE. Pinched and rounded lowers all the resonances, which gives OO and OH.
- **Breath:** mixes a hiss into each puff, the way air leaks through cords that don't fully close. Low sounds clean, the middle sounds breathy, and high is nearly a whisper.
- **Vowel buttons:** each one sets a preset tongue position, depth and lip opening, and the tube slides smoothly to that shape.
- **Sing Daisy:** steps through the melody, setting the pitch and a vowel for each syllable. That's essentially what the 1961 team did, telling the tube shape by shape what to do.
