engineering

GLITS

GLITS is a engineering 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 GLITS rather than just read about it. In short: Graham's Line Identification Tone System (GLITS) is a test signal for stereo systems devised by BBC TV Sound Supervisor and Fellow of the IPS Graham Haines in the mid-1980s. It comprises a 1 kHz tone at 0 dBu (-18 dBFS) on both channels, with interruptions which identify the channels.

Key takeaways

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

Reference excerpt

Graham's Line Identification Tone System (GLITS) is a test signal for stereo systems devised by BBC TV Sound Supervisor and Fellow of the IPS Graham Haines in the mid-1980s. It comprises a 1 kHz tone at 0 dBu (-18 dBFS) on both channels, with interruptions which identify the channels. The left channel is interrupted once for 250 ms every 4 seconds. 250 ms later the right channel has two interruptions of 250 ms spaced by 250 ms. This arrangement has an advantage over the EBU stereo ident tone in that each channel is explicitly identified as belonging to a stereo pair. The EBU Technical Document Multichannel Audio Line-up Tone (Tech 3304) defines stereo lineup tone as having an interruption in the left channel only, lasting 250 ms every 3 s.

Multichannel GLITS There is now an official EBU standard for a multichannel BLITS 5.1 channel ident tone which is also described in the Tech 3304 paper, along with an alternative film-style multichannel ident tone system for systems larger than 5.1 arrays. Blits plays a sequence of tones (based on the musical notes A and E) at -18dBFS on each channel in the AES channel format order (L, R, C, LFE, Ls, Rs), followed by an EBU-style ident on just the front left and right channels, again at -18dBFS and with four interruptions on the left channel. The four interruptions provides a unique confirmation that the stereo or mono downmix came from a 5.1 source and avoids any possible confusion with stereo EBU or GLITS downmixes. The final BLITS tone sequence is a 2 kHz tone at -24dBFS on all six channels – the lower source signal level ensuring that any derived downmixes remain close to -18dBFS. The alternative EBU multichannel ident tone follows a format more closely associated with the film industry. A sustained 80 Hz runs on the LFE channel throughout the sequence. After a 3-second period of constant 1 kHz, -18dBFS tone on all main channels, each channel is identified in turn with a 0.5s pulse of 1 kHz tone, separated from its neighbours by 0.5s silence. The ident sequence starts at Front Left and continues clockwise through each available channel. The amount of time between the 3 second constant tone periods indicates the total number of channels in the system—e.g. a 7.1 system will have an ident sequence lasting 8 seconds. Snell & Wilcox have used the following on the embedded audio in their VALID8 (Video Audio Line-up & IDentification) equipment:

Channel 1 (L) 980 Hz one 250 ms interruption every 4 seconds Channel 2 (R) 980 Hz two 250 ms interruptions every 4 seconds Channel 3 (C) 432 Hz one 250 ms interruption every 4 seconds Channel 4 (Lfe) 432 Hz two 250 ms interruptions every 4 seconds (probably not audible from a subwoofer) Channel 5 (Ls) 990 Hz one 250 ms interruption every 4 seconds Channel 6 (Rs) 990 Hz two 250 ms interruptions every 4 seconds Channel 7 (Lo) 436 Hz one 250 ms interruption every 4 seconds Channel 8 (Ro) 436 Hz two 250 ms interruptions every 4 seconds

References

Worked examples

Example 1 — a first encounter with GLITS

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

In research: GLITS appears in engineering 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 GLITS 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: GLITS is common in secondary-school and first-year university syllabi. It links to neighbouring topics British inventions, Broadcast engineering, Test items, so understanding it makes those chapters shorter.
In everyday life: Look for GLITS 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.

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How to study GLITS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GLITS 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 GLITS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GLITS in simple terms?

Why does GLITS matter?

Because it connects several engineering 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 GLITS?

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 GLITS.