Historically, mbira tunings have not mapped exactly onto Western scales; it is not unusual for a seven-note sequence on a mbira to be "stretched" over a greater range of frequencies than a Western octave and for the intervals between notes to be different from those in a Western scale. Tunings have often been idiosyncratic with variations over time and from one player to another. A mbira key produces a rich complex of overtones that varies from one instrument to another depending on its maker's intentions and accidents of fabrication, such that some instruments simply sound better when some notes of a familiar tuning are pushed. With the increased popularity of the mbira dzavadzimu in North America, Europe, and Japan in recent decades, Zimbabwean mbira makers have tended to tune their instruments more uniformly for export, but much variation is still found among mbira in their homeland.