science

White clipper

White clipper is a 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 White clipper rather than just read about it. In short: A white clipper (or white limiter) is a circuit in professional video products that limits the maximum amplitude of the luminance part of the analogue video signal to 1 volt. It is essential for both analogue recording and transmission of video material.

Key takeaways

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

Reference excerpt

A white clipper (or white limiter) is a circuit in professional video products that limits the maximum amplitude of the luminance part of the analogue video signal to 1 volt. It is essential for both analogue recording and transmission of video material.

Video signal The standard video signal (or more precisely composite video signal) is a signal with a maximum level of 1 volt into 75 Ω. In this signal 0.3 volt corresponds to black and 1 volt corresponds to white. The 0.0 volt to 0.3 volt range is reserved for the sync pulses. Video circuits are designed around these limits. These limits apply to recording on analogue video tape and analogue transmission as well as in analogue to digital video converters. For transmission, the baseband signal modulates the amplitude of the carrier. The modulation index is negative, so higher video level yields lower carrier (RF) level and vice versa. 1 volt (white) video yields only 10% of the full carrier level. The audio signal is frequency-modulated. In a later stage the audio signal is superimposed on the video signal. If, for any reason, the video signal increases beyond 1 volt, the portion of video in excess of 1 volt begins to interfere with the audio signal. The repetition rate of a line is about 15 kHz (15625 Hz in system B and 15750 Hz in system M). The repetition rate of a field is 50 or 60 Hz (50 Hz in system B and 60 Hz in system M). So the interference has two components: a very high-pitched sound of 15 kHz and a low-pitched sound of 50 Hz (or 60 Hz). On the other hand, video input in excess of 1.1 volt results in the loss of the carrier level and this tends to shut down the transmitter. For this reason a white clipper circuit is used to strictly limit the maximum amplitude of the video waveform at the transmitter. For recording and general use the white clipper is used to limit the maximum excursion of the signal. For recording this prevents overmodulation on analogue systems which tends to corrupt adjacent tracks in helical scanning; while on digital systems the peak signal amplitude is an absolute numerical value and cannot be exceeded.

Chrominance A color TV signal is almost the same as a monochrome signal, except that the chrominance signal (a subcarrier modulated by the color information) is superimposed on the monochrome signal (luminance). In a studio environment the total video level while showing a color at maximum saturation (such as yellow) may exceed 1 V. But for transmission, maximum amplitude is limited by the use of the various matrix values in the PAL or NTSC encoder.

The circuit

The white clipper is a circuit that clips out the excess level of video signal. It is especially important for those transmitters that receive signals from other transmitters through professional receivers. The circuit has two parallel arms. In the first arm a Zener diode clips out the signal in excess of 1 volt. In the second arm, the chrominance signal bypasses the Zener diode through a band-pass filter. Sometimes it is necessary or desirable to create a soft clipping action where some highlight detail can be preserved in high contrast scenes. This is known as a "knee" circuit after the shape of the transfer characteristic graph.

Burn-out Video cameras can easily produce over 1 volt in high contrast scenes. However, because the analogue video chain is designed to work within the limits laid out above, the use of the white clipper may result in loss of highlight detail or "burn-out", while a limited contrast ratio is achieved.

See also TV transmitter Residual carrier

References

Worked examples

Example 1 — a first encounter with White clipper

Start with the simplest possible case. Write down what White clipper claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 White clipper 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 White clipper 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 White clipper

In research: White clipper appears in 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 White clipper 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: White clipper is common in secondary-school and first-year university syllabi. It links to neighbouring topics Television technology, so understanding it makes those chapters shorter.
In everyday life: Look for White clipper 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “White clipper” →

Affiliate

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

How to study White clipper in 20 minutes

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

Frequently asked questions

What is White clipper in simple terms?

Why does White clipper matter?

Because it connects several 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 White clipper?

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 White clipper.