There's plenty in the way of competition in the audio transcription market, which is estimated to be worth $31.82 billion by 2025. But AISense -- the startup behind speech-to-text service Otter -- has managed to carve out a niche for itself in the four years since its founding. Today the company confirmed to VentureBeat that it has raised $10 million in a round led by strategic backer NTT Docomo's Docomo Ventures, with participation from Fusion Fund, GGV, Dragon Dragon Fund, Duke University Innovation Fund, Harris Barton Asset Management, Slow Ventures, and others. This brings AISense's total venture capital raised to $23 million, following previous rounds totaling $13 million. As part of Docomo's investment, the Tokyo-based mobile phone operator says it's piloting Otter in Berlitz's English language classes in Japan.