Compressed speech

Time-compressed speech is a technique used, often in advertising, to make recorded speech contain more words in a given time, yet still be understandable.

History
Before electronic methods were developed, spokespeople who could talk extremely quickly and still be understood were widely used, especially for disclaimers.

Methods

 * Removal of silences. There are normally silences between words and sentences, and even small silences within certain words.  These can be reduced considerably and still leave an understandable result.


 * Increasing speed. The speed can be increased on the entire audio track, but this has the undesirable effect of increasing the frequency, so the voice sounds high-pitched (like someone who has inhaled helium).  This can be compensated for, however, by bringing the pitch back down to the proper frequency.

Advantages
The same number of words can be compressed into a smaller time, and thus reduce advertising costs, or more information can be included in a given radio or TV ad. Another advantage is that this method seems to make the ad louder (by increasing the average volume), and thus more likely to be noticed, without exceeding the maximum volume allowed by law.

Disadvantages
The effect of removing the silences and increasing the speed is to make it sound much more insistent, possibly to the point of unpleasantness.

Other uses

 * Teaching and studying.


 * Aids for the blind and disabled.


 * Human-computer interfaces (such as voice-mail systems or lists of movies playing at a theatre)


 * Speech recognition (speeds up or slows down human speech to a speed which can be recognized by the computer)

Other terms
Unfortunately, there are a variety of confusing terms used for this and related technologies:


 * Time-compressed/accelerated speech (often used in psychological literature)


 * Compressed speech


 * Time-scale modified speech (used in signal processing literature)


 * time-scale modification (TSM)


 * Sped-up speech


 * Rate-converted speech


 * Time-altered speech


 * Voice compression/speech compression/voice encoding/speech encoding/audio compression (data) (these often refers to compression for transmission or storage, possibly to an unintelligible state, with decompression used during playback)