A three-step example showing how CTC blanks preserve the repeated n in dinner.

Why “dinner” needs a blank

Connectionist temporal classification (CTC) chooses one letter or blank for each audio frame, or short slice of sound. Blank, written ∅, means “write nothing now.”

Collapse rule: first merge identical letters that touch; then remove blanks. Thus n n → n, but n ∅ n → nn.