Articulation Index

Item Name: Articulation Index
Author(s): Jonathan Wright
LDC Catalog No.: LDC2005S22
ISBN: 1-58563-346-1
ISLRN: 513-688-150-766-0
Release Date: September 15, 2005
Member Year(s): 2005
DCMI Type(s): Sound
Sample Type: pcm
Sample Rate: 16000, 8000
Data Source(s): microphone speech
Application(s): language identification, language modeling, natural language processing, parsing, pronunciation modeling
Language(s): English
Language ID(s): eng
License(s): LDC User Agreement for Non-Members
Online Documentation: LDC2005S22 Documents
Licensing Instructions: Subscription & Standard Members, and Non-Members
Citation: Wright, Jonathan. Articulation Index LDC2005S22. Web Download. Philadelphia: Linguistic Data Consortium, 2005.
Related Works: View


Articulation Index was developed by the Linguistic Data Consortium (LDC) and contains 34 hours of prompted and conversational English speech. The corpus was partly inspired by the work of Harvey Fletcher, who performed a number of perceptual experiments involving English syllables during the first half of the 20th century. His term articulation index meant something like perceptual index of syllables, where those syllables were not necessarily words, and reflected how well speakers could correctly identify syllables in the presence of noise. This corpus was created to facilitate similar experiments, as well as to potentially facilitate new methods in speech recognition research.

The basic concept behind the corpus was to record speakers pronouncing syllables of English, some of which might be real words, but most of which are nonsense syllables. The goal was to have each speaker say a set of 2,000 syllables common to all speakers, as well as a set of 20 syllables unique to that speaker.

LDC has also released Articulation Index LSCP (LDC2015S12), which adds time alignment and different formats to a subset of this corpus.


This release contains recordings of 20 American English speakers (12 males, eight females) saying 2005 common syllables, 1845 of which were spoken by all speakers, and 400 unique syllables (20 syllables/speaker). Participants were prompted with an automatically generated sentence containing the desired syllable followed by an isolated pronunciation of the syllable. The data contains separate files for the whole recorded phrases and the isolated syllables. The corpus also contains short conversations between participants. Here's a breadown of the extent for each folder:

  • Phrases: 22.8 hours
  • Syllables: 10.2 hours
  • Conversation: 1.2 hours

The recordings were made in a small, sound-treated anechoic room at LDC. The speakers wore two microphones: a Sennheiser 410 headset and a Nortel Liberator wireless phone headset. The Sennheiser's signal traveled through a Symetrix 302 Dual Microphone Preamp, Sony PCM-R300 DAT deck, and Townshend Datlink to a Sun Sparcserver 20 where it was written to disk at 16 kHz, 16-bit, pcm data. The Nortel's signal was transmitted to a wireless base station at a telephone connected via the network to LDC's telephone recording platform where it was captured to disk as 8 kHz, 8-bit, u-law data.

The speakers were prompted via a computer interface that displayed one prompt at a time, allowing them to iterate through the prompts by pressing a "next" button. Each recording session lasted approximately 15 minutes.


For an example of the data in this corpus, please listen to this sample (WAV).


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