  Learning speaker-specific features is vital in many applications like speaker
recognition, diarization and speech recognition. This paper provides a novel
approach, we term Neural Predictive Coding (NPC), to learn speaker-specific
characteristics in a completely unsupervised manner from large amounts of
unlabeled training data that even contain many non-speech events and
multi-speaker audio streams. The NPC framework exploits the proposed short-term
active-speaker stationarity hypothesis which assumes two temporally-close short
speech segments belong to the same speaker, and thus a common representation
that can encode the commonalities of both the segments, should capture the
vocal characteristics of that speaker. We train a convolutional deep siamese
network to produce "speaker embeddings" by learning to separate `same' vs
`different' speaker pairs which are generated from an unlabeled data of audio
streams. Two sets of experiments are done in different scenarios to evaluate
the strength of NPC embeddings and compare with state-of-the-art in-domain
supervised methods. First, two speaker identification experiments with
different context lengths are performed in a scenario with comparatively
limited within-speaker channel variability. NPC embeddings are found to perform
the best at short duration experiment, and they provide complementary
information to i-vectors for full utterance experiments. Second, a large scale
speaker verification task having a wide range of within-speaker channel
variability is adopted as an upper-bound experiment where comparisons are drawn
with in-domain supervised methods.
