Reproduction instruments after Denner, Rottenburgh, or Steenbergen each have a characteristic sound. Each instrument maker's product will differ to some degree from another's. Poor response is probably the most common complaint given when players send a recorder for voicing. Good response throughout the range of the instrument sometimes means a compromise in the best tone, and vice versa. An electronic tuner can help you identify problems, but each individual player's breath support and air pressure will be important determining factors in intonation.
Intonation is corrected by modifying the tone holes and, in some cases, the recorder's bore.