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1. General information |
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LibriSpeech is a corpus of read speech, based on LibriVox's public domain |
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audio books. Its purpose is to enable the training and testing of automatic |
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speech recognition(ASR) systems. |
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2. Structure |
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The corpus is split into several parts to enable users to selectively download |
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subsets of it, according to their needs. The subsets with "clean" in their name |
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are supposedly "cleaner"(at least on average), than the rest of the audio and |
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US English accented. That classification was obtained using very crude automated |
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means, and should not be considered completely reliable. The subsets are |
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disjoint, i.e. the audio of each speaker is assigned to exactly one subset. |
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The parts of the corpus are as follows: |
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* dev-clean, test-clean - development and test set containing "clean" speech. |
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* train-clean-100 - training set, of approximately 100 hours of "clean" speech |
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* train-clean-360 - training set, of approximately 360 hours of "clean" speech |
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* dev-other, test-other - development and test set, with speech which was |
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automatically selected to be more "challenging" to |
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recognize |
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* train-other-500 - training set of approximately 500 hours containing speech |
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that was not classified as "clean", for some (possibly wrong) |
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reason |
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* intro - subset containing only the LibriVox's intro disclaimers for some of the |
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readers. |
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* mp3 - the original MP3-encoded audio on which the corpus is based |
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* texts - the original Project Gutenberg texts on which the reference transcripts |
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for the utterances in the corpus are based. |
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* raw_metadata - SQLite databases which record various pieces of information about |
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the source text/audio materials used, and the alignment process. |
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(mostly for completeness - probably not very interesting or useful) |
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2.1 Organization of the training and test subsets |
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When extracted, each of the {dev,test,train} sets re-creates LibriSpeech's root |
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directory, containing some metadata, and a dedicated subdirectory for the subset |
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itself. The audio for each individual speaker is stored under a dedicated |
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subdirectory in the subset's directory, and each audio chapter read by this |
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speaker is stored in separate subsubdirectory. The following ASCII diagram |
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depicts the directory structure: |
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<corpus root> |
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.- README.TXT |
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.- READERS.TXT |
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.- CHAPTERS.TXT |
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.- BOOKS.TXT |
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.- train-clean-100/ |
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.- 19/ |
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.- 198/ |
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| .- 19-198.trans.txt |
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| .- 19-198-0001.flac |
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| .- 14-208-0002.flac |
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| ... |
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.- 227/ |
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| ... |
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, where 19 is the ID of the reader, and 198 and 227 are the IDs of the chapters |
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read by this speaker. The *.trans.txt files contain the transcripts for each |
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of the utterances, derived from the respective chapter and the FLAC files contain |
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the audio itself. |
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The main metainfo about the speech is listed in the READERS and the CHAPTERS: |
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- READERS.TXT contains information about speaker's gender and total amount of |
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audio in the corpus. |
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- CHAPTERS.TXT has information about the per-chapter audio durations. |
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The file BOOKS.TXT makes contains the title for each book, whose text is used in |
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the corpus, and its Project Gutenberg ID. |
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2.2 Organization of the "intro-disclaimers" subset |
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This part of the data contains simply the LibriVox's intro disclaimers that were |
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successfully extracted, using a slight modification of the alignment algorithms |
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used to derive the test training sets. The standard LibriVox disclaimer is: |
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"This is a LibriVox recording. All LibriVox recordings are in the public domain. |
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For more information, or to volunteer, please visit: librivox DOT org" |
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As is the case for the training and test sets, there is one subdirectory for |
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each reader, and a subsubdirectory for each of the chapters, read by this speaker |
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for which the announcement was successfully extracted. |
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2.3 Organization of the "original-mp3" subset |
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This part contains the original MP3-compressed recordings as downloaded from the |
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Internet Archive. It is intended to serve as a secure reference "snapshot" for |
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the original audio chapters, but also to preserve (most of) the information both |
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about audio, selected for the corpus, and audio that was discarded. I decided to |
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try make the corpus relatively balanced in terms of per-speaker durations, so |
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part of the audio available for some of the speakers was discarded. Also for the |
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speakers in the training sets, only up to 10 minutes of audio is used, to |
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introduce more speaker diversity during evaluation time. There should be enough |
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information in the "mp3" subset to enable the re-cutting of an extended |
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"LibriSpeech+" corpus, containing around 150 extra hours of speech, if needed. |
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The directory hierarchy follows the already familiar pattern. In each |
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speaker directory there is a file named "utterance_map" which list for each |
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of the utterances in the corpus, the original "raw" aligned utterance. |
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In the "header" of that file there are also 2 lines, that show if the |
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sentence-aware segmentation was used in the LibriSpeech corpus(i.e. if the |
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reader is assigned to a test set) and the maximum allowed duration for |
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the set to which this speaker was assigned. |
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Then in the chapter directory, besides the original audio chapter .mp3 file, |
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there are two sets of ".seg.txt" and ".trans.txt" files. The former contain |
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the time range(in seconds) for each of the original(that I called "raw" above) |
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utterances. The latter contains the respective transcriptions. There are two |
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sets for the two possible segmentations of each chapter. The ".sents" |
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segmentation is "sentence-aware", that is, we only split on silence intervals |
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coinciding with (automatically obtained) sentence boundaries in the text. |
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The other segmentation was derived by allowing splitting on every silence |
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interval longer than 300ms, which leads to better utilization of the aligned |
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audio. |
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2.4 Organization of the "text" subset |
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This part just contains one subdirectory, with name equal to the ID of the |
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text in Project Gutenberg's database, for each book. The books are also |
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separated in directories by their encoding-- could be either ASCII or UTF-8. |
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The sole purpose of this subset is to be a permanent snapshot of the original |
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text used for LibriSpeech's construction. |
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2.5 Organization of the "raw-metadata" part |
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Contains just few SQLite databases. Some of the more important bits of |
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information from this tables are described in the README file within |
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the "raw_data" subdirectory. |
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Acknowledgments |
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=============== |
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First and foremost, I would like to thank the thousands of Project Gutenberg |
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and LibriVox volunteers, without whose contributions the LibriSpeech corpus |
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would not have existed. |
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The successful completion of this project would have been much more difficult, |
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and the quality of the finished corpus much worse, if it wasn't for the |
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generous support and the many helpful advice, provided by Daniel Povey - thanks, Dan! |
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I would also like to express my gratitude to Tony Robinson, for the very |
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interesting, and useful discussions on the long audio alignment problem, that |
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we had some time ago. |
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Thanks also to Guoguo Chen and Sanjeev Khudanpur, with whom we are collaborating |
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on a (yet-to-be-published) paper on the corpus, and who helped to improve |
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the LibriSpeech's example scripts in Kaldi. |
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--- |
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Vassil Panayotov, |
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Oct. 2, 2014 |
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