Connectionist Temporal Classification (CTC) is a combination of an algorithm and a loss function that transform a sequence of acoustic sounds into a sequence of letters, i.e., speech recognition. Unlike the encoder-decoder structure which transforms a longer input sequence to a shorter output sequence, CTC first transforms the input sequence to an equal length sequence, then transforms the alignment to a shorter output sequence by merging consecutive duplicates and removing blanks. The output vector of the first step is called alignment, and the transformation in second step is called collapsing function.

Connectionist Temporal Classification

Speaker diarization is the task of determining 'who spoke when' in a long multi-speaker audio recording, marking the start and end of each speaker's turns in the interaction. It can be useful for transcribing meetings, classroom speech, or medical interactions. Often times, diarization systems use voice activity detection to find segments of continuous speech, extract speaker embedding vectors, and cluster the vectors to group together segments likely from the same speaker. 

Speaker diarization

The task of wake word detection is to detect a word or short phrase, usually in order to wake up a voice-enable assistant like Alexa, Siri, or the Google Assistant.
The goal with wake words is build the detection into small devices at the computing edge, to maintain privacy by transmitting the least amount of user speech to a cloud-based server.  

Wake word

Speaker recognition is the task of identifying a speaker. We generally distinguish the subtasks of speaker verification, where we make a binary decision (is this speaker X or not?) 

Speaker recognition

University of Michigan - Ann Arbor

- Information extraction
- Machine translation
- Discourse, dialogue and pragmatics
- Natural language generation
- Speech recognition
- Lexical semantics
- Phonology / morphology
- Language resources

Natural language processing in ACM Computing Classification

NLG, a subfield of artificial intelligence (AI), is a software process that automatically transforms data into plain-English content.

Natural language generation

Phonology / Phonetics

Knowledge of the meaningful components of words; more specifically, the way words break down into components that carry meanings like singular vs. plural, I'm, can't, etc.

Morphology

Lexical semantics

Knowledge about linguistic units larger than a single utterance

Discourse

Knowledge of the relationship of meaning to the goals and intentions of the speaker.

Pragmatics

Information extraction

Because the space of possible target sentences is extremely large, a translation system often assigns scores to candidate outputs and uses a search procedure to find a strong result. If the final translation is poor, optimization verification can help determine whether the problem came from search failing to find the best-scoring candidate or from the scoring function itself ranking the wrong candidates too highly.

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