← Speech AI Classroom Kit Main site

Spectrogram Detective

Before a computer can understand a word, it has to read a picture of the sound. Study the clues, then crack eight mystery cards. About 15 minutes, grades 3–12.

🔒 Your answers stay on this page. Nothing is saved or sent anywhere.

1. How to read a sound picture

1

Time runs left to right, like reading a sentence.

2

Low sounds sit at the bottom and high sounds at the top: 0 to 8,000 Hz (vibrations per second).

3

Darker means louder. White means silence.

2. Detective clues

Each sound leaves its own pattern. Study these with a partner before you open the case file.

SDense static filling the top half

Fuzzy static in the top half (above about 4,000 Hz).

SHDense static in the middle

Fuzzy static that reaches lower than S, darkest near 3,000 Hz.

FPale static from low to high

Faint fuzz from low to high. Easy to miss!

STOPWhite gap followed by a thin vertical line

A blank gap, then a thin line: p, t, k, b, d, g.

EEStriped block with a dark band near the bottom and another higher up

Stripes with a dark band high up, near 2,000 to 3,000 Hz.

OOStriped block with dark bands squeezed near the bottom

Stripes with the dark part squeezed near the bottom.

AHStriped block with dark bands close together low in the middle

Dark bands close together in the lower middle. The a in “cat” looks similar.

HUMPale stripes near the bottom only

Faint stripes near the bottom: m and n.

Each thin vertical stripe is one buzz of your vocal folds, so vowels and hums look striped. S, SH and F have no buzz, only rushing air, so they look like static. Clue pictures are idealized; real words blend sounds together, so look for the strongest patterns.

3. The case file

Each picture shows one spoken word. Pick a word for every card, then press Check my answers.

Word bank:

Each word is used exactly once. Stuck? Sort first: which cards start with static? Which end with static? Then look at the vowel bands.

For teachers (includes the solving path)

At a glance

15 minutes · grades 3–12 · pairs · one device per pair, or use the printable version (clue sheet, case file and answer key; black and white is fine).

Run it

  1. Study the clues with a partner (2 minutes).
  2. Match each card to a word (8 minutes). Check my answers marks each card, and wrong cards offer a hint.
  3. Discuss which clue cracked each case (5 minutes). Show all answers explains every card.

Fastest solving path

Cards A, E, F and H start with static; B, C, D and G do not. Endings separate A from E and D from G, and the vowel bands settle the rest.

Discussion prompts

  • Would your voice make the same picture? Children’s voices are higher, so the buzz stripes pack closer together and the dark bands sit higher. That is one reason voice assistants find kids harder to understand.
  • Why don’t computers just follow clues like these? Real speech changes with the speaker, speed and noise. Early systems tried hand-written rules; modern recognizers learn the patterns from many thousands of hours of examples.

Extensions

  • Hard mode: print the case file and hide the word bank.
  • Make your own cards with See Your Voice: say a word, press Pause, then Save picture.
  • AI4K12 connection: Big Idea 1, Perception.

How the pictures were made

Word cards use Windows’ built-in computer voice, so they are cleaner and slower than real speech. Clue tiles are idealized sounds generated from simple models of the voice. Settings: 8 ms analysis window, 0 to 8,000 Hz, darker = louder.

Privacy

No sign-in or ads. Basic page analytics records visits, while answers are checked inside the browser tab and disappear when it closes.