engineering

Pregap

Pregap 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 Pregap rather than just read about it. In short: The pregap on a Red Book audio CD is the portion of the audio track that precedes "index 01" for a given track in the table of contents (TOC). The pregap ("index 00") is typically two seconds long and usually, but not always, contains silence.

Key takeaways

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

Reference excerpt

The pregap on a Red Book audio CD is the portion of the audio track that precedes "index 01" for a given track in the table of contents (TOC). The pregap ("index 00") is typically two seconds long and usually, but not always, contains silence. Popular uses for having the pregap contain audio are live CDs, track interludes, and hidden songs in the pregap of the first track.

Unconventional uses of the pregap

Hidden audio tracks

On certain CDs, such as Light Years by Kylie Minogue, HoboSapiens by John Cale, or Factory Showroom by They Might Be Giants, the pregap before track 1 contains a hidden track. The track is truly hidden in the sense that most conventional standalone players and software CD players will not see it. Such hidden tracks can be played by playing the first song and "rewinding" (more accurately, seeking in reverse) until the actual start of the whole CD audio track. Not all CD drives can properly extract such hidden tracks. Some drives will report errors when reading these tracks, and some will seem to extract them properly, but the extracted file will contain only silence. Other CDs contain additional audio information in the pre-gap area of other tracks, resulting in the audio only being heard on a conventional CD player if the CD is allowed to "play through," but not if you jump to the next track. Of the latter technique, also known as 'backwards indexing', Stylus Magazine cite the James Brown box set Star Time (1991) as a pioneering example, believing it played "a key role in the hidden track evolution once it hit CD." Specifically, Star Time backwards indexes pre-song mundanities such as count ins, false starts and muttering from Brown. Stylus also believe this "nifty device" was effectively employed on the 1995 CD version of the Who's The Who Sell Out to "accommodate the little 'ad jingles' that made the original LP so unique." Some CDs also contain phantom tracks consisting of only index 0 data, meaning the track can only be played on a conventional CD player by allowing the CD to play through a previous track to the next track.

Pregaps in CD-R media

OS support Mac OS X: Currently does not support more than a 2-second pre-gap in the first track under its CD burning utilities. Using a combination of Roxio Toast and a custom .cue file can provide a way around this. Ripping of pregap audio is supported by the application X Lossless Decoder. Windows:

Exact Audio Copy provides the functionality to write to Index 0 Linux:

cdrecord supports writing any kind of pregap cdrdao supports writing any kind of pregap K3B, a frontend for several CD/DVD burning/ripping utilities, supports hiding the first track in the pregap of the second one.

See also List of albums with tracks hidden in the pregap Hidden track List of albums containing a hidden track

Notes

External links Technical Specifications of the Squirrel Nut Zippers "Hot" ECD

Worked examples

Example 1 — a first encounter with Pregap

Start with the simplest possible case. Write down what Pregap 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 Pregap 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 Pregap 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 Pregap

In research: Pregap 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 Pregap 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: Pregap is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio engineering, Compact disc, so understanding it makes those chapters shorter.
In everyday life: Look for Pregap 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 Pregap in 20 minutes

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

Frequently asked questions

What is Pregap in simple terms?

Why does Pregap 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 Pregap?

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 Pregap.