Virtuoso Strings is a dataset for timing analysis and automatic music transcription tasks requiring note onset annotations. The dataset uses real-world multitrack recordings curated as part of the Augmented Reality Music Ensemble (ARME) project, which investigates musician synchronisation and multimodal music analysis. It includes repeated recordings of quartet, trio, duet, and solo ensemble performances with different temporal expressions and leadership role assignments, supporting the development and evaluation of automatic music transcription models across diverse performance styles. To reduce the cost of manual annotation, the dataset uses a semi-automatic method for annotation and quality control. The ISMIR 2023 Late-Breaking/Demo abstract reports 746 tracks with 68,728 onsets, with each track including onset annotations for a single string instrument.