Revision as of 09:44, 3 October 2026

Speakjet Phonetic Guide

The SpeakJet chip produces human speech and sound effects using its built-in **Mathematical Sound Architecture (MSA)**. Instead of playing back recorded audio files (like .WAV files), it uses math models to copy how the human vocal cords, tongue, teeth, and lips move to make sound.

By sending single-byte numbers to the SpeakJet over a serial connection, you can string basic speech sounds together to form any word, sentence, or sound effect in real time.

How Speech Works on the SpeakJet

Human speech is made up of small sound building blocks:

Phoneme: The general family of a sound (for example, the letter sound "T").
Allophone: The exact version of that sound you actually hear, depending on where it sits in a word and what sounds come right before or after it.
- The "T" sound at the start of tea has a sharp blast of air.
- The "T" sound at the end of cat is shorter and softer.
- The "T" sound in the middle of water sounds almost like a soft "D".

The SpeakJet has **72 built-in speech elements (allophones)**. As you send these sound codes to the chip, it smoothly glides the sound from one mouth shape to the next, just like a person talking.

Five Golden Rules for Clear Speech

Follow these five rules to make words sound clear and natural rather than muddy or robotic:

1. Spell by Sound, Not by Letters

English spelling does not match how words actually sound. For example, the letters "c-a-t" sound like "K-A-T", and "ph" sounds like "F". Always spell words using the sound codes that match what your ears hear, not how the word is written on paper.

2. Match Consonants to the Right Vowel

Consonant sounds (like B, D, G, K, S) change depending on whether the vowel that follows them is made in the **front** or the **back** of the mouth:

Use \BE before front vowels (like Bear), but use \BO before back vowels (like Bone).
Use \KE before front vowels (like Key), but use \KO before back vowels (like Comb).
Use \SE before front vowels (like See), but use \SO before back vowels (like So).

3. Use the Right Start or End Sound

Some sounds need special versions depending on where they sit in a syllable:

Starting a word/syllable: Use initial consonants like \BE, \DE, \GE, or \TU.
Ending a word/syllable: Use ending consonants like \EB, \ED, \EG, or \TT.

4. Don't Double Up Sounds Between Words

When speaking normally, people do not stop and repeat the same sound twice between words.

If you say "Night Time", your mouth drops the "T" at the end of "Night" and blends directly into "Time" (saying "Ni-Time").
If you program both "T" sounds back-to-back, the chip will stutter unnaturally.

5. Change the Pitch, Speed, and Bend

A voice that stays at the exact same pitch sounds flat and robotic.

Questions: Raise the pitch code on the last word to make it sound like a question.
Statements: Drop the pitch slightly at the very end of a sentence.
Important Words: Slow down and raise the pitch slightly on the most important word in a sentence to add natural emphasis.

The Vowel Map

Vowels are made by holding your mouth open and changing where your tongue sits (High, Mid, or Low) and whether it is in the Front, Middle, or Back of your mouth. All back vowels are made with rounded lips.

Tongue Height	Tongue Position in Mouth
Tongue Height	Front (Flat Lips)	Middle	Back (Round Lips)
High	`\IY` (128) See, Feed	—	`\UW` (139) Food, June
High-Mid	`\IH` (129) Sit, Pin	—	`\UH` (138) Book, Could
Mid	`\EY` (130) Gate, Beige	`\AX` (133) Cotton	`\OW` (137) Comb, Over
Low-Mid	`\EH` (131) Met, Red	`\UX` (134) Luck, Up	`\OH` (135) Hot, Fox
Low	`\AY` (132) Hat, Fast	—	`\AW` (136) Father, Fall

Long Vowels vs. Sliding Vowels (Diphthongs)

Making Pure Vowels Longer: To make a simple vowel sound longer, either send the same code twice in a row (for example: \IY \IY) or place the SLOW code (8) right in front of it.
Sliding Vowels (Diphthongs): Sounds like \EYIY (the "A" in gate) or \AYWW (the "ow" in cow) are sliding sounds that move from one vowel to another. **Do not repeat these codes back-to-back**, or the chip will repeat the whole slide and sound like it is hiccuping.

Adding Brief Silences Before Pop Sounds

Sounds like P, B, T, D, K, and G need a tiny moment of silence before their release burst so the mouth can "build up air pressure."

The chip adds a tiny gap automatically, but if a word sounds muddy, insert a short silence like Pause 4 (30 ms) or Pause 5 (60 ms) right before the starting pop sound.

Command & Control Codes (0–31, 255)

Send these single byte numbers to control the chip's settings, insert pauses, adjust volume and pitch, or control the digital output pins.

Dec	Hex	Name	Extra Value?	What It Does
`000`	`0x00`	Pause 0	None	0 ms pause. Immediately ramps oscillator volumes down to silent.
`001`	`0x01`	Pause 1	None	100 ms pause. Lowers volume while smoothly moving the sound filters.
`002`	`0x02`	Pause 2	None	200 ms pause. Lowers volume while smoothly moving the sound filters.
`003`	`0x03`	Pause 3	None	700 ms pause. Lowers volume while smoothly moving the sound filters.
`004`	`0x04`	Pause 4	None	30 ms silence. Waits for total quiet before changing filters (good before pop sounds).
`005`	`0x05`	Pause 5	None	60 ms silence. Waits for total quiet before changing filters.
`006`	`0x06`	Pause 6	None	90 ms silence. Waits for total quiet before changing filters.
`007`	`0x07`	Fast	None	Plays the very next sound at half (0.5×) its normal time.
`008`	`0x08`	Slow	None	Plays the very next sound at one-and-a-half (1.5×) its normal time.
`014`	`0x0E`	Stress	None	Tightens the voice slightly for the very next sound (adds emphasis).
`015`	`0x0F`	Relax	None	Loosens the voice slightly for the very next sound.
`016`	`0x10`	Wait	None	Stops speaking and waits for a Start command or pin trigger.
`020`	`0x14`	Volume	0–127	Sets overall loudness. (Default is 96).
`021`	`0x15`	Speed	0–127	Sets speaking speed. (Default is 114).
`022`	`0x16`	Pitch	0–255	Sets voice pitch in Hertz (32 Hz to 240 Hz). Below 30 sounds like clicks. 0 turns voice off. (Default is 88).
`023`	`0x17`	Bend	0–15	Changes voice style from deep/hollow (low) to metallic/tinny (high). (Default is 5).
`024`	`0x18`	PortCtr	0–7	Sets output pin modes for D0–D2. 1 = chip status, 0 = user control. (Default is 7).
`025`	`0x19`	Port	0–7	Sets HIGH/LOW logic output states for pins D0–D2 when user-controlled. (Default is 0).
`026`	`0x1A`	Repeat	0–255	Repeats the very next command or sound code X times.
`028`	`0x1C`	Call Phrase	0–15	Plays an EEPROM phrase and comes back when done (can nest up to 3 deep).
`029`	`0x1D`	Goto Phrase	0–15	Jumps directly to an EEPROM phrase without coming back.
`030`	`0x1E`	Delay	0–255	Waits in steps of 10 milliseconds (from 0 up to 2550 ms).
`031`	`0x1F`	Reset Defaults	None	Resets Volume (96), Speed (114), Pitch (88), and Bend (5) back to standard.
`032–127`	`0x20–0x7F`	Reserved	—	System reserved memory.
`255`	`0xFF`	End of Phrase	None	Marks the end of an EEPROM phrase.

Note: The modifier codes (Fast, Slow, Stress, Relax) only affect the **single sound** that comes immediately after them.

Allophone Speech Sound List (Codes 128–199)

This table lists all 72 basic speech building blocks built into the SpeakJet.

Dec	Hex	Name	Sound Type	Length (ms)	Helpful Usage Tips	Example Words
`128`	`0x80`	`\IY`	Long Vowel	70	High front vowel.	See, Even, Feed
`129`	`0x81`	`\IH`	Short Vowel	70	Short front vowel.	Sit, Fix, Pin
`130`	`0x82`	`\EY`	Long Vowel	70	Mid front vowel. Stressed.	Hair, Gate, Beige
`131`	`0x83`	`\EH`	Short Vowel	70	Standard "e" sound.	Met, Check, Red
`132`	`0x84`	`\AY`	Short Vowel	70	Flat "a" sound.	Hat, Fast, Fan
`133`	`0x85`	`\AX`	Short Vowel	70	Relaxed "uh" sound for unstressed parts.	Cotton, Dust
`134`	`0x86`	`\UX`	Short Vowel	70	Short "u" sound.	Luck, Up, Uncle
`135`	`0x87`	`\OH`	Short Vowel	70	Short "o" sound.	Hot, Clock, Fox
`136`	`0x88`	`\AW`	Short Vowel	70	Deep "ah" sound.	Father, Fall
`137`	`0x89`	`\OW`	Long Vowel	70	Long "o" sound.	Comb, Over, Hold
`138`	`0x8A`	`\UH`	Short Vowel	70	Short "oo" sound.	Book, Could, Should
`139`	`0x8B`	`\UW`	Long Vowel	70	Long "oo" sound.	Food, June
`140`	`0x8C`	`\MM`	Nasal (Nose)	70	Lips together humming sound.	Milk, Famous
`141`	`0x8D`	`\NE`	Nasal (Nose)	70	Use before front vowels.	Nip, Danger, Thin
`142`	`0x8E`	`\NO`	Nasal (Nose)	70	Use before back vowels.	No, Snow, On
`143`	`0x8F`	`\NGE`	Nasal (Nose)	70	"Ng" sound before front vowels.	Think, Ping
`144`	`0x90`	`\NGO`	Nasal (Nose)	70	"Ng" sound before back vowels.	Hung, Song
`145`	`0x91`	`\LE`	Resonant	70	"L" sound before front vowels.	Lake, Alarm, Lapel
`146`	`0x92`	`\LO`	Resonant	70	"L" sound before back vowels.	Clock, Plus, Hello
`147`	`0x93`	`\WW`	Resonant	70	Smooth "W" sound.	Wool, Sweat
`148`	`0x94`	`\RR`	Resonant	70	Standard "R" sound.	Ray, Brain, Over
`149`	`0x95`	`\IYRR`	R-Vowel	200	Combined vowel + R sound.	Clear, Hear, Year
`150`	`0x96`	`\EYRR`	R-Vowel	200	Combined vowel + R sound.	Hair, Stair, Repair
`151`	`0x97`	`\AXRR`	R-Vowel	190	Soft "er" at end of words.	Fir, Bird, Burn, Letter
`152`	`0x98`	`\AWRR`	R-Vowel	200	Combined vowel + R sound.	Part, Farm, Yarn
`153`	`0x99`	`\OWRR`	R-Vowel	185	Combined vowel + R sound.	Corn, Four, Your
`154`	`0x9A`	`\EYIY`	Sliding Vowel	165	Long "A" sound sliding to "E".	Gate, Ate, Ray
`155`	`0x9B`	`\OHIY`	Sliding Vowel	200	Long "I" sound sliding to "E".	Mice, Fight, White
`156`	`0x9C`	`\OWIY`	Sliding Vowel	225	"Oy" sound.	Boy, Toy, Voice
`157`	`0x9D`	`\OHIH`	Sliding Vowel	185	Open "I" sound.	Sky, Five, I
`158`	`0x9E`	`\IYEH`	Sliding Vowel	170	Starting "Y" sound.	Yes, Yarn, Million
`159`	`0x9F`	`\EHLL`	Sliding Vowel	140	Blended "el" at end of words.	Saddle, Angle, Little
`160`	`0xA0`	`\IYUW`	Sliding Vowel	180	"You" sound glide.	Cute, Few, Computer
`161`	`0xA1`	`\AXUW`	Sliding Vowel	170	"Ow" sound.	Brown, Clown, Thousand
`162`	`0xA2`	`\IHWW`	Sliding Vowel	170	Short "oo" glide.	Two, New, Zoo
`163`	`0xA3`	`\AYWW`	Sliding Vowel	200	"Ow" sound.	Our, Ouch, Owl
`164`	`0xA4`	`\OWWW`	Sliding Vowel	131	Long gliding "O" sound.	Go, Hello, Snow
`165`	`0xA5`	`\JH`	Blend	70	Voiced "J" sound.	Dodge, Jet, Savage
`166`	`0xA6`	`\VV`	Buzzing Sound	70	Voiced "V" buzzing sound.	Vest, Even
`167`	`0xA7`	`\ZZ`	Buzzing Sound	70	Voiced "Z" buzzing sound.	Zoo, Zap
`168`	`0xA8`	`\ZH`	Buzzing Sound	70	Soft buzzing "sh" sound.	Azure, Treasure
`169`	`0xA9`	`\DH`	Buzzing Sound	70	Voiced "th" sound.	There, That, This
`170`	`0xAA`	`\BE`	Pop Sound	45	Start of word; before front vowels.	Bear, Bird, Beed
`171`	`0xAB`	`\BO`	Pop Sound	45	Start of word; before back vowels.	Bone, Book, Brown
`172`	`0xAC`	`\EB`	Pop Sound	10	End of word; after front vowels.	Cab, Crib, Web
`173`	`0xAD`	`\OB`	Pop Sound	10	End of word; after back vowels.	Bob, Sub, Tub
`174`	`0xAE`	`\DE`	Pop Sound	45	Start of word; before front vowels.	Deep, Date, Divide
`175`	`0xAF`	`\DO`	Pop Sound	45	Start of word; before back vowels.	Do, Dust, Dog
`176`	`0xB0`	`\ED`	Pop Sound	10	End of word; after front vowels.	Could, Bird
`177`	`0xB1`	`\OD`	Pop Sound	10	End of word; after back vowels.	Bud, Food
`178`	`0xB2`	`\GE`	Pop Sound	55	Start of word; before front vowels.	Get, Gate, Guest
`179`	`0xB3`	`\GO`	Pop Sound	55	Start of word; before back vowels.	Got, Glue, Goo
`180`	`0xB4`	`\EG`	Pop Sound	55	End of word; after front vowels.	Peg, Wig
`181`	`0xB5`	`\OG`	Pop Sound	55	End of word; after back vowels.	Dog, Pug
`182`	`0xB6`	`\CH`	Blend	70	Sharp "ch" sound.	Church, Feature, March
`183`	`0xB7`	`\HE`	Hissing Sound	70	"H" sound before front vowels.	Help, Hand, Hair
`184`	`0xB8`	`\HO`	Hissing Sound	70	"H" sound before back vowels.	Hoe, Hot, Hug
`185`	`0xB9`	`\WH`	Hissing Sound	70	"Wh" blowing sound.	Who, Whale, White
`186`	`0xBA`	`\FF`	Hissing Sound	70	"F" air hissing sound.	Food, Effort, Off
`187`	`0xBB`	`\SE`	Hissing Sound	40	"S" sound before front vowels.	See, Vest, Plus
`188`	`0xBC`	`\SO`	Hissing Sound	40	"S" sound before back vowels.	So, Sweat
`189`	`0xBD`	`\SH`	Hissing Sound	50	"Sh" air sound.	Ship, Fiction, Leash
`190`	`0xBE`	`\TH`	Hissing Sound	40	Quiet unvoiced "th" sound.	Thin, Month
`191`	`0xBF`	`\TT`	Pop Sound	50	Middle or end of words.	Part, Little, Sit
`192`	`0xC0`	`\TU`	Pop Sound	70	Sharp start of words.	To, Talk, Ten
`193`	`0xC1`	`\TS`	Blend	170	"Ts" ending sound.	Parts, Costs, Robots
`194`	`0xC2`	`\KE`	Pop Sound	55	Start of word; before front vowels.	Can't, Clown, Key
`195`	`0xC3`	`\KO`	Pop Sound	55	Start of word; before back vowels.	Comb, Quick, Fox
`196`	`0xC4`	`\EK`	Pop Sound	55	End of word; after front vowels.	Speak, Task
`197`	`0xC5`	`\OK`	Pop Sound	45	End of word; after back vowels.	Book, Took, October
`198`	`0xC6`	`\PE`	Pop Sound	99	Start of word; before front vowels.	People, Computer
`199`	`0xC7`	`\PO`	Pop Sound	99	Start of word; before back vowels.	Pod, Paw, Copy

Sound Effects & Tone List (Codes 200–254)

The SpeakJet also has 55 built-in sound effects, sirens, creature sounds, and telephone touch-tones.

Robot Chatter Sounds

Short, 80 ms electronic sounds useful for robotic chatter, button clicks, and sci-fi effects.

Dec	Hex	Name	Time	Sound Type	Best Used For
`200–209`	`0xC8–0xD1`	`\R0` to `\R9`	80 ms each	Robot	Quick electronic clicks, sci-fi computer sounds, and robotic chatter.

Sirens & Warning Alarms

Sustained pitch sweeps for alarms and alerts.

Dec	Hex	Name	Time	Description
`210`	`0xD2`	`\A0`	300 ms	Fast mid-pitch chirp siren.
`211`	`0xD3`	`\A1`	101 ms	High electronic blip.
`212`	`0xD4`	`\A2`	102 ms	Low alert tone.
`213`	`0xD5`	`\A3`	540 ms	Rising multi-tone siren sweep.
`214`	`0xD6`	`\A4`	530 ms	High warbling siren.
`215`	`0xD7`	`\A5`	500 ms	Loud industrial warning horn.
`216`	`0xD8`	`\A6`	135 ms	Fast intrusion alarm beep.
`217`	`0xD9`	`\A7`	600 ms	Rising two-tone siren sweep.
`218`	`0xDA`	`\A8`	300 ms	Continuous ringing bell sound.
`219`	`0xDB`	`\A9`	250 ms	Repeating alert beep.

Beeps & Button Feedback

Dec	Hex	Name	Time	Description
`220`	`0xDC`	`\B0`	200 ms	Clean confirmation beep.
`221`	`0xDD`	`\B1`	270 ms	Mid-pitch chime.
`222`	`0xDE`	`\B2`	280 ms	Low error / rejection buzz.
`223`	`0xDF`	`\B3`	260 ms	High-pitch success beep.
`224`	`0xE0`	`\B4`	300 ms	Resonant dual-tone blip.
`225`	`0xE1`	`\B5`	100 ms	Very short click.
`226`	`0xE2`	`\B6`	104 ms	High button tap sound.
`227`	`0xE3`	`\B7`	100 ms	Low thud tap sound.
`228`	`0xE4`	`\B8`	270 ms	Rising two-note chime.
`229`	`0xE5`	`\B9`	262 ms	Falling two-note cancel sound.

Biological & Animal Sounds

Dec	Hex	Name	Time	Description
`230`	`0xE6`	`\C0`	160 ms	Short bird chirp / click.
`231`	`0xE7`	`\C1`	300 ms	Low frog croak / throat growl.
`232`	`0xE8`	`\C2`	182 ms	High bird trill.
`233`	`0xE9`	`\C3`	120 ms	Quick animal squeak.
`234`	`0xEA`	`\C4`	175 ms	Cricket chirp sound.
`235`	`0xEB`	`\C5`	350 ms	Deep creature groan.
`236`	`0xEC`	`\C6`	160 ms	Short throat grunt.
`237`	`0xED`	`\C7`	260 ms	Rising creature screech.
`238`	`0xEE`	`\C8`	95 ms	Wet throat pop.
`239`	`0xEF`	`\C9`	75 ms	High bug chitter / click.

Telephone Keypad (DTMF) Tones

Standard dual-tone telephone keypad numbers. Each tone plays for 95 milliseconds.

Dec	Hex	Name	Phone Key	Low Tone	High Tone	Time
`240`	`0xF0`	`\D0`	Key 0	941 Hz	1336 Hz	95 ms
`241`	`0xF1`	`\D1`	Key 1	697 Hz	1209 Hz	95 ms
`242`	`0xF2`	`\D2`	Key 2	697 Hz	1336 Hz	95 ms
`243`	`0xF3`	`\D3`	Key 3	697 Hz	1477 Hz	95 ms
`244`	`0xF4`	`\D4`	Key 4	770 Hz	1209 Hz	95 ms
`245`	`0xF5`	`\D5`	Key 5	770 Hz	1336 Hz	95 ms
`246`	`0xF6`	`\D6`	Key 6	770 Hz	1477 Hz	95 ms
`247`	`0xF7`	`\D7`	Key 7	852 Hz	1209 Hz	95 ms
`248`	`0xF8`	`\D8`	Key 8	852 Hz	1336 Hz	95 ms
`249`	`0xF9`	`\D9`	Key 9	852 Hz	1477 Hz	95 ms
`250`	`0xFA`	`\D10`	Key *	941 Hz	1209 Hz	95 ms
`251`	`0xFB`	`\D11`	Key #	941 Hz	1477 Hz	95 ms

Miscellaneous Sounds

Dec	Hex	Name	Time	Sound Type	Description
`252`	`0xFC`	`\M0`	125 ms	Sonar Ping	Deep-water submarine ping. (The chip plays this during Baud Rate setup).
`253`	`0xFD`	`\M1`	250 ms	Gunshot	Sharp pistol blast.
`254`	`0xFE`	`\M2`	530 ms	"WOW" Sound	Vocal sweep moving up and down.

Practical Code Examples

Always End with Pause 0

When you finish sending a phrase, always send a Pause 0 (code 0). This tells the chip to turn the volume gracefully down to zero. If you don't, the speaker may pop or buzz when playback stops.

Example 1: Saying "Ready"

Break the word into four basic sounds:

Starting "R": \RR (148)
Short "e": \EH (131)
Front "D": \DE (174)
Ending "ee": \IY (128)
Finish with silence: Pause 0 (0)

// C code array to say "Ready"
const uint8_t SPK_READY[] = { 148, 131, 174, 128, 0 };

Example 2: "System Alert" with Siren and Pitch Change

This example plays an alarm horn, speaks in a firm, lower pitch, pauses between words, and raises the pitch on the word "Alert":

const uint8_t SPK_SYSTEM_ALERT[] = {
    // 1. Reset standard sound settings
    31,                  // Reset defaults (Volume: 96, Speed: 114, Pitch: 88, Bend: 5)
    20, 110,             // Volume up to 110
    22, 70,              // Pitch down to 70 Hz (Lower, serious tone)

    // 2. Play Warning Horn
    215,                 // Alarm A5 (500 ms)
    5,                   // Pause 5 (60 ms silent gap)

    // 3. Speak "SYS-" (\SE, \IH, \SE)
    187, 129, 187,
    // "-TEM" (\TU, \EH, \MM)
    192, 131, 140,
    
    2,                   // Pause 2 (200 ms break between words)

    // 4. Raise pitch for "ALERT"
    22, 85,              // Pitch raised to 85 Hz for emphasis
    130,                 // "A-" (\EY)
    145, 14, 151, 191,   // "-LERT" (\LE, \Stress, \AXRR, \TT)

    // 5. Clean finish
    0                    // Pause 0 (Fade to silence)
};

Example 3: Dialing a Phone Number

Transmits the touch-tones for "555-1212" with brief pauses:

const uint8_t SPK_DIAL_SEQUENCE[] = {
    245, 6, 245, 6, 245, 2,      // 5, 5, 5 with small gaps and a 200 ms break
    241, 6, 242, 6, 241, 6, 242, // 1, 2, 1, 2
    0                            // Mute when done
};

Glossary of Terms

Allophone: A specific version of a basic speech sound. For example, the "T" sound in top has a strong burst of air, while the "T" sound in stop is softer. Both are allophones of the letter "T".

Bend: A setting (0–15) on the SpeakJet that changes the sound filters. Lower values make the voice sound deeper and hollow; higher values make it sound sharp and metallic.

Diphthong (Sliding Vowel): A vowel sound that glides smoothly from one mouth shape to another within a single syllable, such as the "oy" in boy or the "ow" in cow.

Fricative (Hissing / Buzzing Sound): A sound made by squeezing breath through a narrow opening in the teeth, lips, or tongue. Examples include "S", "Z", "F", "V", and "TH".

Nasal (Nose Sound): A sound produced by letting air pass through the nose rather than the mouth, such as "M" and "N".

Phoneme: The basic building-block sound family in a language. Changing a phoneme changes the meaning of a word (like changing the "B" in bat to a "C" to make cat).

Pitch: How high or low a voice sounds, like musical notes on a keyboard. Pitch is measured in cycles per second (Hertz).

Pop Sound (Stop Consonant): A sound made by completely blocking the airflow in your mouth for a split second and then releasing it with a burst, such as P, B, T, D, K, and G.

Resonant: A smooth, singing consonant sound that lets air flow freely through the mouth without hissing or buzzing, such as "L", "R", and "W".

Voiced Sound: A speech sound made while your vocal cords are vibrating. If you gently touch your throat while humming an "M", buzzing a "Z", or saying "AH", you can feel the vibration.

Voiceless (Unvoiced) Sound: A speech sound made purely with rushing air, without using your vocal cords. Examples include whispering, "S", "F", and "T".

Difference between revisions of "Speakjet Phonetic Guide"