ArticleslgStudy

computer science

Scratch input

Scratch input is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Scratch input rather than just read about it. In short: In computing, scratch input is an acoustic-based method of Human-Computer Interaction (HCI) that takes advantage of the characteristic sound produced when a fingernail or other object is dragged over a surface, such as a table or wall. The technique is not limited to fingers; a stick or writing implement (e.g., chalk or a pen) can also be used.

Scratch input — main illustration
Scratch input — illustration

Key takeaways

  • Scratch input belongs to computer science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Scratch input to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Scratch input from memory before moving on to harder problems.

Reference excerpt

In computing, scratch input is an acoustic-based method of Human-Computer Interaction (HCI) that takes advantage of the characteristic sound produced when a fingernail or other object is dragged over a surface, such as a table or wall. The technique is not limited to fingers; a stick or writing implement (e.g., chalk or a pen) can also be used. The sound is often inaudible to the naked ear (i.e., silent). However, specialized microphones can digitize the sounds for interactive purposes. Scratch input was invented by Mann et al. in 2007, though the term was first used by Chris Harrison et al.

History A natural interface for musical expression operating on scratch input principles was first published and presented in June 2007. Later that year, it was extended to an implementation on a smartphone and also a wearable computer system. In 2008, the Scratch Input project demonstrated a mobile device input system utilizing scratch input, simultaneously popularizing the term. This system captured audio transmitted through a surface on which a mobile phone was placed, enabling the entire surface to be used as an input device.

Uses Scratch input is an enabling input technique used in a multitude of applications. The earliest application was a highly expressive musical instrument (Mann et al.) for use with mobile devices on natural objects, surfaces, or the like, as a non-synthesizing (i.e. idiophonic) musical instrument. Harrison et al. proposed it to create large, ad hoc gestural input areas when mobile devices are rested on tables.

Commercial potential Microsoft has expressed interest in Scratch Input.

With this we can start to think of every flat surface as an potential input area. If mass produced this sensor could cost less than a dollar....Despite the limitations, the technology holds enough promise to make it into the hands of consumers. It is exciting because it is so low cost. This idea has the potential to go beyond just a research project.

See also Scratch Input with ice skates Vision-assisted Scratch Input Scratch Input explanation and demonstration

References

Illustrations

Scratch input: Scratch input using geophones (contact microphones) bonded to each fingernail as a musical instrument. The awful sounds generated by running fingernails down the chalkboard are separately pitch-corrected, resulting in a pleasant-sounding musical instrument.
Scratch input using geophones (contact microphones) bonded to each fingernail as a musical instrument. The awful sounds generated by running fingernails down the chalkboard are separately pitch-corrected, resulting in a pleasant-sounding musical instrument.
Scratch input: Scratching a stick on bricks and mortar, with vision-assisted gesture recognition. This gives better results than scratch input alone. (Public performance in Toronto, Ontario; image from the 2007 paper.)
Scratching a stick on bricks and mortar, with vision-assisted gesture recognition. This gives better results than scratch input alone. (Public performance in Toronto, Ontario; image from the 2007 paper.)
Scratch input: Scratch input with ice skates is called a pagophone.[3]
Scratch input with ice skates is called a pagophone.[3]

Worked examples

Example 1 — a first encounter with Scratch input

Start with the simplest possible case. Write down what Scratch input claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Scratch input before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Scratch input ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Scratch input

In research
Scratch input appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Scratch input in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Scratch input is common in secondary-school and first-year university syllabi. It links to neighbouring topics Canadian inventions, Experimental musical instruments, Human–computer interaction, so understanding it makes those chapters shorter.
In everyday life
Look for Scratch input outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Scratch input in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Scratch input means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Scratch input out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Scratch input in simple terms?

In computing, scratch input is an acoustic-based method of Human-Computer Interaction (HCI) that takes advantage of the characteristic sound produced when a fingernail or other object is dragged over a surface, such as a table or wall. The technique is not limited to fingers; a stick or writing imp…

Why does Scratch input matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Scratch input?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Scratch input.

Tags

  • Canadian inventions
  • Experimental musical instruments
  • Human–computer interaction
  • User interfaces

Keep exploring