Kenneth in the Machine: The Acorn Speech System

Pull up a chair, grab a brew, and let’s travel back to 1982. Today, we are opening up the beige case of the BBC Micro to install one of the most distinctive and futuristic upgrades of the 8-bit era: The Acorn Speech System.

In the early 1980s, home computing was a silent affair, punctuated only by the click of mechanical keyboards and the occasional harsh beep from a piezoelectric speaker. If a computer wanted to communicate, it did so through green text on a black screen. But Acorn, never one to follow the herd, decided the "Beeb" should be able to talk back.

However, they didn't want it to sound like a generic, soulless robot from a B-movie. They wanted it to sound authoritative, educated, and distinctly British. They wanted it to sound like the BBC.

Enter Kenneth Kendall. The legendary newsreader and presenter of Treasure Hunt was hired to record the phonemes and phrases that would eventually be squeezed into two ROM chips. Through some clever engineering, his voice was immortalized in silicon, giving the BBC Micro the most polite, articulate, and stiff-upper-lip voice in computing history.

How It Works: The Digital Throat

To understand how a newsreader fits inside a mere 16KB of ROM, you have to appreciate the constraints of the time. Storing high-quality digital audio (like a modern WAV or MP3) requires massive amounts of memory - far more than the 32KB available in the Model B.

Acorn’s engineers turned to a technique called Linear Predictive Coding (LPC).

The Science of Simulation

Standard audio recording stores the shape of the sound wave itself. LPC, however, discards the sound wave and instead stores a "recipe" for the human vocal tract that created it. It essentially asks: "What shape was Kenneth's mouth in when he said this sound?"


The result is a synthesized approximation of Kenneth Kendall’s voice. It isn't a recording; it is a "Robot Kenneth" constantly reconstructing speech from mathematical equations in real-time. This allowed Acorn to compress speech down from 64,000 bits per second (standard telephone quality) to a mere 1,200 bits per second—a staggering achievement in compression.

Installation Guide: Giving the Beeb a Voice

Warning: This procedure involves handling static-sensitive chips and working inside the computer. Ensure your BBC Micro is unplugged, and you are grounded before touching the motherboard.

If you have managed to scour eBay or a retro fair and acquire a TMS5220 speech processor and the two TMS6100 PHROMs (Phrase ROMs), here is how to install them.


Remove the four screws securing the lid: two on the back panel and two underneath the front edge. Lift the lid carefully, minding the keyboard ribbon cable.


Look at the front-left area of the motherboard, near the keyboard connector. You are looking for empty sockets labeled IC98, IC99, and IC100.



The BBC Micro is a hobbyist's dream, full of jumper links to configure hardware.

User Instructions: Making Kenneth Speak

Once installed, the Speech System integrates seamlessly into the BBC Micro's operating system. It hijacks the standard SOUND command, utilizing negative channel numbers to distinguish speech from the standard musical tone generator.

The syntax is:

SOUND -1, word_index, 0, 0

Where...

A Quick Test

Type this at the prompt and press Return. You should hear a polite, slightly robotic "Hello":

SOUND -1, 125, 0, 0

The "Talking Clock" Example

This program demonstrates how to mix BASIC logic with speech. It makes Kenneth count down from 10 to 0.

10 REM A Simple Countdown
20 FOR I% = 10 TO 0 STEP -1
30   PRINT "Count: ";I%
40   REM Kenneth has different intonations for "Zero"
50   IF I% = 0 THEN SOUND -1, 32, 0, 0 ELSE SOUND -1, I%, 0, 0
60   REM Create a delay so he doesn't speak too fast
70   T% = TIME : REPEAT UNTIL TIME > T% + 100
80 NEXT I%
90 REM Say "Ready"
100 SOUND -1, 158, 0, 0 

The Comprehensive Vocabulary List

The Speech System doesn't have a text-to-speech engine in the modern sense; it cannot read any word you type. Instead, it has a fixed dictionary of about 165 words and sounds. To use it effectively, you need the Index Number for each word.


Kenneth is excellent at math. Note that "Ten" appears twice; Index 1 is the "counting" ten ("eight, nine, ten"), while Index 264 is a flatter "statement" ten ("it is ten o'clock").


These indices correspond directly to the ASCII codes of the keyboard keys. If you feed the ASCII value of a letter to the sound command, Kenneth says that letter.


The dictionary was heavily curated for the classroom. You'll find words for error reporting ("Mistake", "Escape"), units of measurement ("Centimetre", "Hertz"), and BASIC commands.


What if you want Kenneth to say a word that isn't in the ROM, like "Space"? You have to build it manually using phonemes and fragments. This requires patience and a good ear, as you are essentially stitching together sounds.

Pro Tips for the Café Regulars