Q: "Does the hardware version of Auto-Tune work for all instruments?"

A: First, understand that the Antares ATR-1a works for monophonic instruments only. In other words, it corrects one pitch at a time. As far as range goes, the ATR-1a was designed to detect and correct pitches up to the pitch C6. If the input pitch is higher than C6, the ATR-1a will often interpret the pitch an octave lower. This is because it interprets a two cycle repetition as a one cycle repetition. On the low end, the ATR-1a will detect pitches as low as A0 (55Hz) in its normal mode and down to 25Hz when Bass Mode is selected. This range of pitches allows intonation correction to be performed on all vocals and almost all instruments.